Kazakh – British Technical University

UDС 541.13; 546.22; 546.221; 621.2.035.2 Retaining manuscript rights

TOKTAR GULMIRA

Obtainment inorganic compound of sulfur by electrochemical methods

6D072000 – Chemical technology of inorganic compounds

Dissertation for the degree of

Doctor of Philosophy (PhD)

Supervisor: the winner of the state

prize of the Republic of Kazakhstan

Corresponding Member National

Academy of Sciences.,

d.c.s., Professor Bayeshov A.B

Scientific adviser: Director Faculty of

Science and Engineering,

Manchester Metropolitan University, UK

PhD, Professor Graig E. Banks

Republic of Kazakhstan

Almaty, 2016

2

CONTENT

DEFINITIONS.........…………………………………………………………... 4

SYMBOLS AND ABBREVIATIONS................................................................5

INTERDUTION..................................................................................................6

1 SULFUR AND ITS COMPOUNDS PRESENT ISSUES, PHYSIC-

CHEMICAL PROPERTIES AND THEIR IMPACT ON THE

ENVIRONMENT……………………………………………………………………9

1.1 Physic-chemical properties of sulfur and its compounds................................9

1.2 The distribution sulfur in the nature and its application.................................14

1.3 Electrochemical properties of sulfur and its compounds...............................14

1.4 Е-pH diagram of sulfuric- water system.........................................................25

1.5 Sulfur content Oil and sulfur-containing waste sources impact on the

environment.................................................................................................................32

2 EXPERIMENTAL METHODS AND IMPLEMENTATION OF

TECHNOLOGY........................................................................................................35

2.1 Methods of potentiodynamic polarization curves recording...........................35

2.2 Preparation of current conductor sulfur-graphite composite electrodes and the

methodology of electrolysis.........................................................................................37

2.3 Used reagents, drugs and analysis of the obtained products..........................41

2.4 Determination of sulfur-containing compounds by physico-chemical

methods........................................................................................................................42

3 ELECTROCHEMICAL PROPERTIES OF ANODE POLARIZED

SULFUR ELECTRODE’S IN THE SOLUTION OF HYDROCHLORIC

ACID………………………………………………………………………………...48

4 ELECTROCHEMICAL PROPERTY OF SULFUR IN SODIUM

CHLORIDE, AND CARBONATE SOLUTION…………………………………...52

4.1 Dissolution of anode polarized elemental sulfur in sodium chloride solution.52

4.2 Electrochemical properties of dissolution elemental sulfur by formation of

sulfate-ions in sodium carbonate solution....................................................................55

5 ELECTROCHEMICAL PROPERTIES OF ELEMENTAL SULFUR IN

ALKALINE SOLUTIONS.........................................................................................59

5.1 Cathodic electrochemical property of elemental sulfur dissolved in sodium

hydroxide solution.......................................................................................................59

5.2 In alkaline solution dissolved elemental sulfur oxidation with the formation of

sulfate ions...................................................................................................................62

5.3 Investigation of electrochemical properties of elemental sulfur preliminary

dissolved in alkaline solution by recording the anodic and cathodic potentiodynamic

polarization curves.......................................................................................................67

5.4 Obtainment of monosulfide and investigate its electrochemical properties by

unloading polarization curves......................................................................................71

3

6 RECEIVE OF COPPER SULFIDE AND ITS ELECTROCHEMICAL

BEHAVIOR...............................................................................................................83

7 CREATION OF CHEMICAL POWER SOURCE BY USING

OXIDATION REACTIONS ON THE SULFUR COMPOSITION

ELECTRODE............................................................................................................89

7.1 The regularities of formation of motive force in the galvanic pair of "sulfur-

graphite" - "lead dioxide".............................................................................................89

CONCLUSION..................................................................................................95

REFERENCES..................................................................................................97

ADDITIONAL A -Auther Certificate………………………………….......106

4

DEFINITIONS

In this dissertation following terms and definitions are used:

Anode – electrode in an electrochemical cell on which the oxidation reaction

occurs.

Cathode– electrode in an electrochemical cell on which the reduction reaction

occurs.

Electrochemistry– a field of chemistry that focuses on the interchange between

electrical and chemical energy.

Sulfide – an inorganic anion of sulfur with the chemical formula S2−. It

contributes no color to sulfide salts. As it is classified as a strong base, even dilute

solutions of salts such as sodium sulfide (Na2S) are corrosive and can attack the skin.

Sulfide is the simplest sulfur anion.

Electrolysis – the decomposition of a substance by means of electric current. This

method pushes a redox reaction toward the non-spontaneous side.

Electrolytic cell – electrochemical cell that is being pushed toward the non-

spontaneous direction by electrolysis.

Electromotive force, EMF (or cell potential) – difference of potential energy of

electrons between the two electrodes.

Flotation agents– reagents that selectively adsorbed on the mineral surface,

which must be translated into a lather, and giving the particles hydrophobic properties

Oxidation– lose of electrons, can occur only in combination with reduction.

Reduction– gain of electrons, can occur only in combination with oxidation.

Redox reaction– shorthand for reduction-oxidation reaction.

Voltaic cell or galvanic cell– an electrochemical cell that uses redox reaction to

produce electricity spontaneously

5

SYMBOLS AND ABBREVIATIONS

Іa – Anodic current;

Іc – Cathodic current;

I – Current, А

J – Current density, А/m2;

Еа – Anodic potential, V;

Еc – Cathodic potential, V;

ƞ – Current efficiency, %;

t – Electrolyze time, hour;

С – Solution concentration;

V – Scan rate, mV/sek;

Еа – Activation energy, kJ/mol;

E⦵ – Standard electrode potential, V;

Е – Electrode potential, V;

T – Thermodynamic temperature, К;

R – Universal gas constant;

XR – X-ray analysis;

IR – Infrared spectra;

mt – Theoretical mass;

F – Number of Faraday;

n – Number of electrode;

k – Electrochemical equivalent, mEq/l;

mp – Practical mass, g.

6

INTRODUCTION

The actuality of work. All countries, including our republic, there are many

problems in the field of full and effective use of natural resources and the application

of wastes as a raw material.

Most of the Kazakhstan oil is considered that possesses medium or high-sulfur

content. Large quantities of by-product sulfur are being produced as a result of the

removal of hydrogen sulfide from the oil and gas produced in the region. And also the

elemental sulfur which accumulates in the territory during the purification is as

agarbage. At the same time, sulfur compounds contain fuels and lubricants impact on

corrosivon exposure of internal combustion motors, to reduce its capacity and the

cleanliness of the environment. This is not only on the territory of our country, but also

causing global environmental problems all aroung the world. Accumulated elemental

sulfur in the oil and gas industry of the republic is not being found fully used. Sulfur is

used in the production of 30 thousand names of production. This phosphate fertilizer,

paper, rubber, asphalt, paint, textiles, plastic and even cosmetics. It is also used in the

nuclear industry, through the production of sulfuric acid, which is used for leaching of

uranium ore. It should also be noted that one of the indicators of industrialization of

any country is the production of sulphuric acid. In this regard, to create simple methods

to obtain variety sulfur compounds necessary for the production is a very important

and one of the actual problems. A detailed knowledge of the physical and chemical

properties of sulfur is essential in the theoretical basis to produce optimized sulfur

compounds

The objective of work and tasks. The purpose of the work: Comprehensive study

on electrochemical properties of polarized sulfur in alkaline, acid and neutral mediums

and to investigate synthesis methods of important inorganic compounds.

Depending on the purpose of the work is expected to accomplish the following

tasks:

- to study the effect of main electrochemical paremeters(current density,

electrolyte concentration, electrolysis duration) for the anodic dissolution of sulfur

composite electrode during the polarization;

- depending on the state of the electrochemical polarization, to determine the

current output of generated electrolysis products;

- to investigate electrochemical properties of polysulfide solution obtained by

elemental sulfur preliminarily dissolved in alkaline solution by the method

ofelectrochemical polarization and removing the anodic and anodic-cathodic

potentiodynamic polarization curve;

- to obtain sodium monosulfide and study its electrochemical properties by

unloading of potentiodynamic polarization curves;

- to receive copper sulfide and to study the influence of various parameters

(current density, electrolyte concentration, electrolysis duration) for the formation of

copper sulfide;

- to study the possibilities to use sulfur-graphite composite electrode as a negative

electrode of galvanic element on the basis of its oxidation reaction.

7

The objective of study. To propose a new method to obtain inorganic sulfur

compounds by using electrochemical proces.

Connection with the plan of basic scientific research. The dissertational work

is carried out as a part of a research project of 2012-2014 y., funded by the Committee

of Science of Ministry of Education and Science of RK «By electrochemical

technology processing to obtain sodium sulfide from the sulfur waste» and 2015-2017

y., «Development of electrochemical technology to producing a new generation of

modern flotation reagent – calcium sulfide and luminophores – sulphides of zinc and

cadmium from sulfur with manufacturing and the creation of its pilot installation»

(Electrochemical labarotory at Institute of Fuel, Catalysis and Electrochemistry after

named D.V Sokolsky)

Scientific novelty of the thesis. – In this thesis for the first time, anodic oxidation

of elemental sulfur in alkaline, acidic and neutral medium investigated

comprehensively by using specially prepared electric conducted composite sulfur-

graphite electrodes;

- for the first time, the results of the analysis by the method of IR spectroscopy

for the product was given which formed by dissolving elemental sulfur powder in a

solution of sodium hydroxide, this obtained product’s the formation regularities of

sulfate ions on the anode side and sulfide ions on the cathode side were studied by the

method of electrolysis in the electrode space allocated electrolyzer;

- electrochemical properties of preliminary elemental sulfur dissolved in a

solution of sodium hydroxide electrolyte for the first time investigated by removing the

anodic and anodic-cathodic potentiodynamic polarization curves, the result shown that

oxidation of polysulfide ions to elemental sulfur was stage process;

- proposed a new the method of obtaining sodium monosulfide and its

electrochemical properties for the first time researched by unloading potentiodynamic

polarization curves, and identified that oxidation of monosulfide ions to elemental

sulfur was complicated process and which carried out in diffusion mode;

- a new and simple method to get copper sulfide powder was proposed, for this

powder were done X-ray and elemental analysis, as a result of elemental analysis

identified that the composition of the powder contained 63.63% copper and 31.03% of

the sulfur;

- the possibility to use composite sulfur- graphite electrode as negative electrode

were considered during the obtainment chemical power, there "sulfur-lead dioxide "

galvanic element be provided 1050 can mV of electromotive force;

- for the first time shown that elemental sulfur can be used to get electric current.

The novelty of this method was protected by innovation patent of RK №. 31177.

The theoretical value and practical significance. According to the carried out

research works results for the frist time shown that from sulfur can synthes in the

national economy widely used inorganic compounds of sulfur which in the Republic

of Kazakhstan as waste have been delisted into the environment. At the same time was

shown that elemental sulfur can be used to obtain electric current.

Accuracy of the results and conclusions which given doctoral thesis. Research

8

work modern, high-precision measuremention by the methods of I-160 IM, photo

calorimeter, Autolab PGSTAT 302N (potencostat galvanostat) installations and

physico-chemical methods (IR) and element analysis are confirmed and formulated

electrochemical kinetic calculations.

Personal contribution of the author. In the work carried out in collaboration

and included in the thesis is to carrying out research and analysis of literature data, the

experimental solution of set tasks, interpretation and generalization of the results and

publication of research results in the form scientific conferences and scientific papers.

Approbation of practical results of the work. The main results of work were

presented at the following international conferences, seminars and forums: "Innovative

development and relevance of science in modern Kazakhstan" VIII International

Scientific Conference (Almaty, 2014), "International Conference on Chemical

Engineering and Advanced Materials" (China, 2016), "The new science: from idea to

results" international Scientific Conference (Russia, 2016).

Publications. The main content of the dissertation was published in 11 works in

the open press, which include:

- 1 inovation patent Republic of Kazakhstan;

- 6 articles published in journals recommended by Committee on Control of

Education and Science of the Ministry of Education and Science of Republic of

Kazakhstan;

- 1 articles published in international journals having non-zero impact factor

included into the Scopus databases;

-3 materials and theses in international, national, scientific meetings and

conferences (one of them is registered into the Thomson Reuters and Scopus

databases).

Content and structure of the dissertation. The thesis consists of introduction,

7 chapters, conclusions, list of literature sources. In the thesis, consisting of 106 pages,

including 60 figures and 6 tables. List of bibliographic literature consists of 149

domestic and foreign literature sources.

9

1 SULFUR AND ITS COMPOUNDS PRESENT ISSUES, PHYSIC-

CHEMICAL PROPERTIES AND THEIR IMPACT ON THE ENVIRONMENT

Now a day, in Kazakhstan oil and gas industry, not only increased in the direction

of oil and gas production, but also towards the creation and implementation of

innovative technologies for the processing of its waste have been developped. Sulfuric

acid is charged from sulfur, through the acid could carried out the process of leaching

of important elements to the solution from the ore, fertilizers and explosive substances

are taken. Many of the world's oil processing factories the huge amount of elemental

sulfur are collected as an additional product [1].

Production and processing of sulfuric oil and gas condensate raw materials, as

well as, by increasing of deep cleaning of sulfur from oil, elemental sulfur’s formation

size is grown sharply. That is why, to find ecological clean and safe way for long-term

storage of accumulated sulfur and to obtain its important compounds are today’s issue

[2].

There are some disadvantages of modern technologies of processing of generated

wastes during the oil and gas production, including an undevelopped domestic

technologies on profoundly cleaning of sulfur from oil; application of imported

catalysts; modern experimental installations used less for industrial research. One way

to solve the caused problem– to use high technologies for oil and gas processing,

including the development of technologies for the processing of sulfur which is the

most extensive residual was occurred during oil and gas production [3].

Understanding of physical and chemical properties of sulfur, knowledge of

molecular and crystal structure, which is very important to create its various industrial

processing technologies.

In order to solve this serious problem, necessary to comprehensively study

properties of elemental sulfur and its compounds. As well as, causes the necessity

research of electrochemical properties of sulfur and its compounds. Based on the

investigation of anodic-cathodic reation mechanisms accompanied on the sulfur

electrode are leads to determine the possibilities of creation new methods.

1.1 Physic-chemical properties of sulfur and its compounds

Sulfur (sulfur) is chemical element in VI group on the periodic system with

symbol S and atomic number 16 and atomic mass 32.06. Sulfur has 25 known isotopes,

four of which are stable 32S(95.084%), 33S(0.74%), 34S(4.16%), 36S(0.016%) [4]. These

electrons are divided into three layers, electronic formula of sulfur: 1s22s22p63s23p4.

Sulfur II, IV, VI can be valent, and oxidation state of sulfur - 2, 0, +4 and +6.

Radius of sulfur atom 0.104 nm. Ions of radius 0,170 nm (coordination number equal

to 4). Energy of sulfur atoms from S0 - to S6+ (10.36, 23.35, 34.8, 47.3, 72.5 and 88.0

eV). Elemental sulfur occurs naturally as the element (native sulfur), but most

commonly occurs in combined forms as sulfide and sulfate minerals. The amount of

sulfur weight on the earth 0.05%, on the sea water 0.08-0.09% [5,6 ].

Physical properties of sulfur. Elemental sulfur is a bright yellow crystalline solid

at room temperature. hydrophobic sulfur insoluble in water, soluble in benzene, carbon

10

and that is fragile solid. It melts at 119 °C, boils at 444.6 °C. External valences layers

of sulfur atom have two independent electronic that is why they can communicate. The

nature could occurs in the form free mode and minerals of sulfide (pyrite, galena,

antimonite, etc.), sulfate (gypsum, anhydrite, barite, mirabilis, etc.). Several crystalline

forms of sulfur has been known, including stable form are rhombic α-sulfur and

monoclinic β-sulfur. The density of sulfur is about 2 g·cm−3 for example which twice

heavy than water [9]. Poor conducted heat and current, thermal conductivity is 0.208

W / (m • deg). The number of atoms in the molecule sulfur gradually reduced when

heated sulfur: S8→ S6→ S4→ S2, finally, at temperatures above 2000 °C, sulfur steam

appears in the individual atoms. Allowed to cool this process reversed and occurs the

polymerization phenomenon [10].

According to the scientific work [11] were mentioned that allotropic states of

sulfur allocated three groups: cyclo-octasulfur, polymeric sulfur, intermediate sulfur.

Including well-known crystal allotropic modifications of cyclo-octasulfur are rhombic

S (to 95.62 оС) and monoclinic -β (95.6-119.3 оС). Rhombic modification of sulfur

transferred to monoklinge release heat as follows:

Sα → Sβ + 2,4 kcal. (1.1)

Three modifications of liquid state sulfur are known S S + S 12, if cool it

down quickly, metastable modification may formatted. Depending on the ways to

obtain solid sulfur permanent on a metastable state micro impurities basis may be

consist eight ring S8 cycles modifications. Between them poor connections is

determined low electrical conductivity of sulfur.

Chemical properties of sulfur. Sulfur in their compounds shows from -2 to +6

oxidation degrees. Sulfur reacts with nearly all the elements exception of gold,

platinum, iridium, nitrogen, tellurium, iodine and the noble gases [13-16], as well as

the reactions metals are released a very large amount of heat. With oxygen formatted

several oxide [17].

Redox potentials of sulfur passage from one state to another, Depending on the

medium are equal following values:

S-2 → S0 → S+4 → S+6 (1.2)

Acidic medium, В: +0.14, +0.15, +0.17 (1.3)

Alkaline medium, В: -0.48, -0.61, -0.91 (1.4)

Sulfur insoluble in aqueous medium, but its same modification soluble in organic

solution (toluene, benzene) and carbon sulfur, liquid ammonia NH3.

Colorless and pungent smell of sulfur oxides is obtained by burning of sulfur in

the air:

S + O2= SO2 (1.5)

Basically, spectral analysis identified that the process of oxidation of sulfur to

11

sulfur dioxide was serial and proceeds with generating of intermediate products (sulfur

oxide S2O2, molecular sulfur S2, free sulfur atoms S and free radicals of sulfur oxide

SO).

Sulfur plays a role of reduction with interaction of other non-metallic:

S + 3F2= SF6 (1.6)

On Harold work was shown that interaction of sulfur alloy with chlorine formed

sulfur dichloride and dithiodichloride 18:

2S + Cl2= S2Cl2 (1.7)

S + Cl2= SCl2 (1.8)

When heated sulfur reacts with phosphorus formed P2S5 phosphorus sulfide 19:

5S + 2P → P2S5 (1.9)

Moreover, when heated by adding hydrogen obtained H2S hydrogen sulfide and

(H2Sn) sulfan:

H2 +S = H2S (1.10)

Sulfur could react with many metals by releasing high amount of heat, for

example: iron, copper, etc. sulfur reduced by reacting metals formed their sulfides [20]:

Fe + S = FeS (1.11)

2Na + S = Na2S (1.12)

Obtained sulfides do not stable, in contrast, composition can be variable. As well

as the composition of the calcium sulfide changed from CaS to CaS5. And polysulfides

obtained in the form of CaSn and Na2Sn, and sulfan is formed by interaction of

hydrochloric acid (value of n can be between 1-10).

Sulfur dissolved in concentrated nitric acid, and concentrated sulfuric acid

changed sulfur (IV) oxide [21-24]:

S + 6HNO3 = H2SO4 + 6NO2 + 2H2O (1.13)

S + 2H2SO4 = 3SO2 + 2H2O (1.14)

And liquefied nitrogen, hydrochloric and sulfuric acids do not react with sulfur at

room temperature, elemental sulfur disproportioned alkaline solution or boiled hot

water.

Research of Shulek [25, 26], between sulfur and boiling water accompanied

hydrolysis reaction by the following formula:

12

2S +2H2O →H2S +H2SO2 (1.15)

When the pH ˂ 7, disintegration of H2SO2 the following formula:

H2SO2→SO2+S +2H2O (1.16)

When the pH˃7:

2H2SO2→S2S32−+ H2O+2H+ (1.17)

Near neutral solutions, at temperature to 100 °C and the following reaction

occurred:

4S +3H2O →2 H2S+ S2S32−+2H+ (1.18)

When the temperature is higher than 100 °C, in Bendassoli [27,] work shown that

the reaction of the sulfur with water will be held in two stages, in the first stage occurred

H2S and SO2:

3S + 2H2O ↔ H2S + SO2 (1.19)

In the second stage at 400 °C occurs disintegration of H2S:

H2S ↔ 2H2 + S2 (1.20)

Work [28] was told that the main product the reaction of sulfur with water at

temperature is higher than 260 °C were ions of sulfide and sulfite.

3S + 3H2O ↔ 2H2S + H2SO3 (1.21)

Here is equilibrium concentration of H2S at 25 °C, only 10-7 g-ion/l, experimental

research cause very difficult and does not give a unique information.

According to the data [29] solid sulfur reacts with sodium hydroxide, polysulfide

and sodium thiosulfate reacted as follows:

(2n+4)S + 6NaOH →2Na2Sn+1 + Na2S2O3 + 3H2O (1.22)

Around temperature of 100 °C sulfur will react aqueous solution of sodium

hydroxide and disproportionated [30]:

1/2S8 +4OH- → S2 +2HS- + 3H2O (1.23)

In this direction, Schuler and Keresh were contributed a lot and [25, 31] work

shown disproportion reaction of sulfur and sodium hydroxide occurs by following:

13

2nS +6OH- → S2O32−+ 2S𝑛−1

2− +3H2O (1.24)

By following reaction may formed ions of polysulfide and sulfite:

9S +6OH- → 2S42−+ SO3

2− + 3H2O (1.25)

3S + 6NaOH = 2Na2S + Na2SO3 + 3H2O (1.26)

With increasing of sodium hydroxide concentration the ratio of S𝑛2−/S2O3

2−

decreases. This could shows by following stoichiometric equation:

6S +3OH- →1/2 S2O32− + S5

2− + 3/2 H2O (1.27)

6S +6OH- → S2O32− + S2

2− + 3H2O (1.28)

Sulfur reacts with sulfide could formed polysulfide-ions:

Na2S + (n-1)S = Na2Sn (1.29)

Reacts sulfur with sodium sulphite, a compound of sodium thiosulfate (Na2S2O3)

is formed:

Na2SO3 + S = Na2S2O3 (1.30)

Heated sulfur could reacts with nearly all other elements including gold, platinum,

iridium, nitrogen, tellurium, iodine and the noble gases.

Also many of sulfur oxides are well known. From stable sulfur oxide obtained

(sulfur gaz, sulfur anhydride, sulfur oxide (IV)) and from sulfur trioxide SO3 (sulfur

gaz, sulfur anhydride, sulfur oxide (VI)) were taken except that could got unstable

oxides S2O, (SO2 sent smoldering current) and S8O (hydrogen sulfide (H2S) interact

with SOCl2) are charged. And peroxides (SO4 and S2O7) were formed discharge of SO2

flame by a mixture of oxygen or oxidation of SO2 with ozone. Acidic sulfur dioxide

(SO2) corresponds to the average strength unstable sulfuric acid (H2SO3):

H2O + SO2 → H2SO3 (1.31)

In addition, sulfur trioxide acid, SO3 accordance with the strong sulfuric acid:

SO3 + H2O → H2SO4 (1.32)

As well as sulfur, sulfuric acid corresponds to two series of salts: acide

(hydrosulfides NaHSO3, Ca(HSO3)2 and hydrosulfates KHSO4, NaHSO4 etc.) and

medium (sulfides Na2SO3, K2SO3 and sulfates CaSO4, Fe2(SO4)3).

Low dispertion sulfur at room tempearture could react with alkaline and formed

thiosulfate and thiofulfide.

14

Sulfur reacts with many organic compounds such as saturated hydrocarbons. The

reaction of sulfur with olefins very important which used for vulcanization of natural

and synthetic caoutchouc [32].

1.2 The distribution sulfur in the nature and its application. Sulfur was known

in China since the 6th century BC, "pure sulfur" the name as natural mineral means

"combustible stone". In 1777, Antoine Lavoisier proved that sulfur is not compound

just a simple element. Now a days, the sulfur-containing medicines fights against

meningitis bacteria and sulfur containing cream helps fight skin diseases. In 1839,

Charles Goody a mixture of rubber and sulfur spill fire accidentally. Goody received

a "burning" rubber called by the name of Roman God - the owner of the fire Volcano.

In 1867, underground ore sulfur was opened Louisiana and Texas [33].

The prevalence of sulfur in nature took 16th place among all the elements. It

consists in the earth's crust, seawater and even the composition of meteorites [34].

Sulfur occurs widely across the globe and high sulfur oil and gas processing

locations. For example, sulfur could meets in the USA, Canada, as well as Asian

countries. Canada is the largest sulfur exported country and the largest imported

country is china.

In recent years, sulfur reserves in storage has increased gradually. That is, in 1999,

the world warehouses motionless elemental sulfur was 22 million. As well as sulfur

market depending on the type, quality and transfer fee of product. International trade

sulfur, in the last 15 years mainly increased 20% by expense of granulated and liquid

sulfur trading [35].

Today, Kazakhstan reserves of sulfur takes second place in the world. Once upon

a time "Tengizchevroil" united enterprise collected more than12 million ton of sulfur.

By 2020, there is a risk of amount of sulfur increases several times in the Republic of

Kazakhstan [36]. Sulfur mainly used in the chemical industry to obtain sulfuric acid,

as well as paper, rubber, in creation of matches, in textile fabric bleaching, drugs,

cosmetics drugs preparation, plastic, explosive substances, in agricultural crops very

important biogenic substance and widely used for receiving toxic chemicals [37-39].

1.3 Electrochemical properties of sulfur and its compounds

Sulfur dielectric, so they do not carry electrical current. Sulfur is insoluble in

water, so its polarography properties investigated in anhydrous organic solvents [40].

Sulfur is stable oxidizing agents of aqueous and acid solutions. However, it is

unstable in alkaline solution that could disproportionated HS-, S2-, and formed other

oxidant products.

During the electrochemical practices of chalcogenes, the reaction occurs slowly

and only in the presence of heat in concentrated alkaline medium. Alkaline metals and

earth metals soluble in water although same of their sulfides insoluble but they soluble

in various rank of acid medium. The possibility of oxidation of sulfur was determined

by the method polarography. Sulfide ions electrochemical oxidized in aqueous

solutions depends on their experimental conditions the formation possibility of

elemental sulfurs – polysufide, sulfate, thiosulfate and dithionite were identified.

15

Polarography condition thiosulfate, sulfoxides and sulfon are considered organic active

compound.

Electrochemical properties of elemental sulfur with formation of polysulfide

anions is provided comprehensively in organic solvents (DMF, DMA, DMSO, CH3CN,

etc.) and mmonium liquids [42].

Interpretation of this process significant results achieved dimethylformamide

(DMF) solution [43]. Electrochemical properties of sulfur investigated in alkaline

medium (NaOH + H2O solution) [44].

In sulfur-sulfide system’s electrochemical properties research, the main work

directed on to receive chloride sulfur-based batteries in sulfur-polysulfide and chloride

alloys. Because of poorly dissolution of elemental sulfur in water, to study its

electrochemical reduction do not allowed in aquatic medium. However,

electrochemical regularities of sulfide (HS- , S2-) and polysulfide ions in aqueous

solution in less studied than anhydrous solution.

Anyway, A number of carried out research to study electrochemical behaviours

of sulfur aqueous sulfur-sulfide system, sulfur redox regularities were considered by

absorption of sulfur and its compounds on variety of substrate electrodes and on the

basis of formation of sulfur compounds in solution [45-47].

Electrochemical properties of sulfur-polysulfide are widely studied in organic

solution and same of salt alloys.

Electrochemical properties of sulfur and polysulfides studied in ionic liquids. On

authors’ [48] work studied in details on reduction of sulfur and proved that reduction

process is occurred by change of one or more electrons each reduction peak

accompanied with chemical modification and said presence of this process directly

depend on solution, reference electrolyte and nature of electrode. Reduction S8 of in

organic solution (THF, DMF, DMSO, or CH3CN), when use different electrodes

(Pt, graphite, glass, carbon and Au), usually carried out with two electronic stage. An

additional, smaller wave situated between the two main reduction peaks has been

observation and most authors [49-51] showed the presence of acidic impurities:

The first reduction peak for S8, its 2 electron losing by following reaction:

S8 + 2e- →S82− (1.33)

Often proposed to be shown by following reaction:

4S82−→ 4S6

2−+ S8 (1.34)

S62−→S3

.− (1.35)

Kim and Park [52] also suggest formation of S42− and S3

2− (by 1.36 and 1.37

reaction) based on UV-vis spectro-electrochemical experiments.

2S82− → 2S4

2− + S8 (1.36)

S82− + S6

2− → 2S32− + S8 (1.37)

16

The second reduction wave has been attributed to different processes, including

the 2-electron reduction of 𝑆82− to 𝑆8

4− which may dissociate into𝑆42− (1.38, 1.39

reaction) or the reduction of 𝑆62− or 𝑆3

.− to 𝑆32−(1.40, 1.41 reaction) [53].

S82− + 2e- → 2S8

2− (1.38)

S84−→ 2S4

2− (1.39)

S62− + 2e- → 2S3

2− (1.40)

S3.− + e- → S3

2− (1.41)

In chloroamuminate (AlCl3/NaCl ), the electrochemistry of elemental sulfur is

further complicated by the formation of chlorinated species such as S2CI2 and SCI3+,

normally, four oxidation and four reduction waves observed in same system [54-56]. Nevertheless,

reduction to 𝑆82− is also proposed to occur at the first voltammetric wave in AlCl3/NaCl

melts. It has also been shown that elemental sulfur can be easily reduced to other sulfur species by

dissolving it at certain temperature in same phosphonium and imidazolium inic liquids [57].

Figure 1.1 – UV-vis spectra of solution of N2S6 and N2S4 in (a) [C4 mim][DCA]

and (b) DMSO

According to the result, the spectrum of N2S4 shows an absorption band band at c

nm whereas that of N2S6 depicts a band at nm with a shoulder at ca. 350nm. These date

agree well the absorption spectra reported for the two dianions S42− and S6

2− in organic

solvents (table 1.1).

Table 1.1 - Absorption maxima (λmax/nm) assigned to sulfur species observed during

the electrochemical reduction of S8 in molecular solvents (DMSO and DMF; Literature

Values) and λ max obtained in this work for [C4mim][DCA]

Solvent S2− S2

2− S32− S4

2− S52− S6

2−

S72− S8

2− S3.− S4

.− Rep

17

Сontinuation table 1.1

1 2 3 4 5 6 7

8 9 10 11 12

DMSO 435 505 618 13

420 475 492 618 14

260 350,

450

340,

450

379,

490

610 770 17

DMF 498 617 18

250 280 334 420 435 442,

450 470,490 (S8

2−liner),

355 (S82−

cyclic) 600

˷700 20

[C4mim][DCA 440 350,

460

620 In this

work

Oxidation of sulfide ions. During the anodic oxidation of sulfide ions in ionic

solution, depending on the circumstances formed elemental sulfur, polysulfide, sulfate,

dithionate and thiosulfate ions. Bohnholtzer and Heinrich [58] are carried works on

smooth platinum electrode wire identified that discharge of S2- ions occurred by

formation of polysulfide and elemental sulfur, shown that sulfur easily dissolves in

polysulfide solution. Grischer [59] found that sulfur melted in a Na2S2 solution with

the highest rate. He [60] oxidation of S2- ions was studied by removing polarzation

curves. On the research of Bohnholtzer and Heinrich were identified three potential

area: a – from 0- to +0.9 V; b – from +0.9-to +2.1 V; с – from +1.6-to +2.5 V. In this

three area formed different products. ''А'' area formed only polysulfides, and are of ''b''

– obtained polysulfide-, sulfate- , thiosulfate- ions, there output of ploysulfide

decreased by the increasing, but output of sulfate is grown; ''с'' area formed only sulfate

ions. There is no formation of ions dithionate ions.

Grischer believes that following electrode reactions accompanied:

On the potentials of in the area ''a'':

SX2− → xS + 2e (1.42)

And

SX2− + S → SX−1

2− (1.43)

On the area of ''b'':

S2- + 6OH- → SO32− + 6e + 3H2O (1.44)

SX2− + 6OH- → S2O3

2−+ 6e + 3H2O + (x-2) S (1.45)

18

The next reactions:

2 SO32−→ S2O6

2−+ 2e (1.46)

SO32−+ S → S2O3

2− (1.47)

2 S2O32− → S4O6

2−+ 2e (1.48)

4S4O62- +6OH → 5S2O6

2−+ 2S2O62−- + 3H2O (1.49)

S3O62- + 2OH- → S2O3

2− + SO42−+ + H2O (1.50)

In the area of '' c '' potential is defined by the following reactions:

SO32−+ 2OH- → SO4

2− + 2e + H2O (1.51)

S2O32−+ 2OH- → SO4

2−+ 2e + H2O + S (1.52)

On the work of A. Baeshov, and Blazhako the anode oxidation of sulphide-ions

were studied on the electrode of platinum and copper group metals [61-64]. The

polarization curves were taken these mentioned metals on stationary and rotating disk

electrodes under argon atmosphere. By previously research shown that sulfide ions in

1M NaOH solution oxdaized on platinum electrode and the oxidation is observed from

+1.0 V positive potential and was said that cathodic polarization curve of copper and

silver electrodes in sulfide-alkaline solution only only one current maximum recorded

which for copper electrodes at 0.9 V and silver electrodes - 0.65V.

Kuit university scientists [65],oxidation of sulfide ions on ploycrystalic platinum

electrode studied by cyclic voltametry, An electrolyte of 3.5% NaCl containing of

sulfide ions was used as the testing medium.

Accprding to the research, the following anodic reactions are expected to occur in

the sulfide system, resulting in the formation and removal of sulfur layer:

HS- + OH- → S + H2O + 2e- (1.53)

S2-→ S + 2e- (1.54)

2HS- + 2OH- →S22− + 2 H2O + 2e- (1.55)

HS- + 9OH- →SО42−+ 5H2O + 8e (1.56)

S + HS- + OH- →S22− + H2O (1.57)

S + S22− →S3

2− (1.58)

19

Figure 1.2 – Effect of HS- ions concentration on the cyclic voltammograms

(polycrystalline platinum at scan rate 10 mV/s)

Study the effect of pH sulphide containing electrolyte prodominate species HS- is

in this electrolyte values from 9 to 12. It is shown that anode current taken cycle

voltomogramms in the presence of sulfide ions increased significantly than

involvement of sulfide ions solution (figure1.2), which explained by auther anodic

oxidation of sulfide ions.

In the presence of sulfide ions, only anodic currents are measured in the forward

sweep while the magnitude of currents in the reverse sweep in negligibly small. This

indicates that the products of the anodic reaction in the forward sweep do not undergo

reduction in the reverse sweep and have passivated the platinum surface. Three features

appear in the forward sweep, marked a, b and c at potentials of -0.1, 0.475 and 1.0 V,

respectively. While features a and c readily defined, feature b is less clear. a small

shoulder at point (b) is formed which may be due to the starting point of the deposition

of elemental sulfur. The starting of formation of white thin layer adherent to the

electrode surface was observed exactly at this potential. Such formation causes the

reduction in the size of effective surface of the Pt electrode. The formation of large

peak afterward at point (c) (see figure 1.2) can be explained on the basis of the

oxidation of the deposited sulfur according to the equation (equation 1.61) to form

soluble sulfate ions. The phenomenon of periodic formation and dissolution of sulfur

element on the Pt electrode could be represented as follows:

Pt + HS- + OH- → PtS + H2O + 2e- (1.59)

20

PtS + HSx− → Pt + HSx−1

− (1.60)

PtS + 8OH- →Pt +4 H2O + SO42− + 6e- (1.61)

The above mechanism is substantiated by XPS performed on the electrodes

surface after potentiostatic experiments. Many XPS spectra of polycrystalline platinum

polarized at different potentials in sulfide polluted salt water were measured. An

illustrative example of these spectra is shown in figure-1.3. It shows XPS spectrum of

platinum electrode polarized at a potential of 1.0 V for 60 minutes 3.5% NaCI + 0.15

M HS-. A sharp S2p peak appears at 163.2 eV, which is characteristic of the presence

of elemental sulfur (S) on the electrode. A small shoulder appears at 169.2 eV which

indicates the presence of sulfate (SO42−) ions.

Figure 1.3 – XPS spectrum of a polycrystalline platinum electrode after

potentiostatic polarization at 1.00 V (Ag/AgCl) for 1 hour in presence of 3.5 % NaCl

solution containing 0.15 M HS- at 25 °C

Cyclic voltamograms of polycrystalline platinum show negligibly small currents

in the absence of sulfide ions compared to those measured in its presence, at all

potentials. These anodic currents are indeed resulting from the oxidation of the sulfide

ions. The magnitude of currents measured in the reverse sweep is much less than those

measured in the forward sweep which reveals that the reaction products in the forward

sweep have passivated the platinum surface. Three current peaks appear in the forward

sweep at potentials of -0.1, 0.475 and 1.0 V, respectively. The first peak indicates the

possibility of the formation of platinum sulfide and polysulfide. The second peak may

be due to the starting point of the deposition of elemental sulfur. A white thin layer

21

adherent to the electrode surface starts exactly at this potential. The third peak can be

explained on the basis of the oxidation of the deposited sulfur to form soluble sulfate

ions.

Oxidation and reduction of elemmental sulfur. [66] In authors work studied

reduction of sulfur suspension, and they shown that on lead and zinc cathode

unreduction in sulfuric acid and alkaline solutions. But in netural and alkaline solution

on graphite reduced with output of 55-75%. Current density does not affect for this

process. The reduction in acid solutions as state of suspension of elemental sulfur,

widely used for obtaining hydrogen sulfide [67, 68].

In the study oxidation of sulfur on platinum, nickel and stainless steel electrodes,

the results of polarization curves of on the electrodes identified that the oxidation of

sulfur was implemented to oxygen separation potential. Which, on platinum electrode

"plus" 1.13 V, on stainless steel "plus" 0.86 V and on nickel - "plus" 0.80V. In the

presence of dispersed sulfur, the distribution of oxygen voltage increased, comparison

with the testing solution should be noted that the shift to the right side which explained

that gradually passivation of electrode surface and absorption of sulfur on the electrode.

As a result of polarization curves proved that the oxidation potential of sulfur

powder due to the electrode material.

On the basis of standard redox potentials on the anodic oxidation of sulfur to

sulfite and sulfate ions reactions could be assumed by following reaction:

S + 8OH˗ - 6e- ↔SO42− + 3H2O, E0 = - 0,660V (1.62)

S + 8OH˗ - 6e- ↔SO42− + 4H2O, E0 = - 0,753V (1.63)

The formation of sulfite and sulfate ions after anodic polarization of dispersed

sulfur, electrolysis products confirmed by the results of chemical analysis.

The effects of alkali concentration for the oxidation process sulfur studied on

platinum electrode. With increase of alkaline concentration oxygen separation potential

moves toward the negative side, that is why when concentration of alkaline higher than

5 M oxidation of sulfur wasn’t observed.

Baeshov and his scientific staff [69] predict when sulfur powdered, its particles

are charged negatively by this verified following, if immediately polarize after crushing

of sulfur on cathode, on polarization curve on the lead electrode its reduction clear

waves weren’t observed. Which explained negatively charged sulfur particles alienated

from cathodic polarized electrode and as a result, dispersion of sulfur on the surface of

the cathode electrode would not adsorbed.

But in the condition of anodic polarization, sulfur particles on the positively

charged anode surface because of involved in electrostatic it can be seen its oxidation

occurs easily.

After neutralization of negative charge of dispersed sulfur, its particles reduction

speed increased that displayed as clear maximum on polarization curve. In the literature

[70] has confirming data about sulfur could have a strong negative charge after

grinding.

Oxidation and reduction of thiosulfate. In previously works have been made

22

prognosis that thiosulfate oxidized separated oxygen from anode.

Professor the electrochemical state of thiosulfate studied by taking voltametric

curves on P-5827 potentiostat under potentiodynamic regime[71]. As a electrode

material were used platinum, copper, nickel and stainless steel. As a reference electrode

was used silver chloride electrode and as a counter electrode was used graphite rod.

There work potentials are given by the participation of normal hydrogen electrode.

When thiosulfate ion anodic oxidized on platinum nickel, stainless steel and

copper, oxidation waves were registered all mentioned electrodes polarization curves.

Second waves was appeared at the potential of +0.7 V and the studied compound’s

anodic oxidation results can see visually by the surface of copper electrode lined with

the black sediment and identified that was copper (II) oxide. This phenomenon cites a

decision the possiblity of oxidation of thiosulfate ions on copper electrode

accompanied by complex mechanisiom.

Muhmoud [72] was studied the electrochemical reduction of sodium thiosulfate

in aqueous media on platinum electrode. Na2S2O3 solution containing sulfuric acid

(H2SO4) at pH =3 the cathodic reduction was observed around -0.6 V. And in this

electrochemical reduction reaction can be determined to know the mechanism of the

reaction by the following equation:

/𝐸𝑝-𝐸𝑝/2/= 1.857𝑅𝑇

𝑎𝑛𝑓 =

47.7

𝑎𝑛 mV (1.64)

The influence of electrolyte concentration for the reduction of thiosulfate anion

was studied in the range of 0.001-0.0075 M (figure 1.4). There is a slight decrease in

the reduction peak current density which explained by a weaker dissociation at higher

concentrations of thiosulfate anion.

In addition, at low pH levels, a colloidal sulfur is generated which is distributed

and adsorbed on the electrode surface. This retards the electron transfer process at these

concentrations.

The effect of temperature on electrochemical reduction of thiosulfate anion was

investigated for 0.005 M in the temperature range between 20 and 50 °C. The peak

current was increased by the increasing of temperature (figure 1.5). This indicates that

the temperature increase causes the electroreduction process to take place more easily

on the Pt- electrode surface, due to the decrease in the activation energy.

23

Figure 1.4 – Dependence of the reduction peak current on the concentration of

thiosulfate anion at v=20 mV/s at pH= 3 and t=22 °C

Figure 1.5 – LSV of 0.005M Na2S2O3 on Pt- electrode at pH= 3 Scane rate

5mV/s at different temperatures

24

The oxidation of thiosulfate was studied by using the method of cycle

voltogramma [73]. According to the resolute shown that the oxidation process was

sensitive value of pH and scan rate (figure 1.6).

Figure 1.6 – LSV of 0.5 mol.l-1 of thiosulfate solution on various pH value

Seen from Figure, when the pH 5 or 6 on the cyclic voltomogramma was

registered three oxidation waves which 0.05 V, 0.58V and 1.02V. Increase in pH value

with the decreasing scan rate, oxidation peak on 0.05V was observed. When the pH

value is 8 ~ 9, can be seen in three obvious oxidation peak, approximately 0.05V, 0.91V

and 1.22V. If increase scan rate the values of the cyclic voltomagromma curves closed

one to another and the system will disappeared However, when increase the pH value

than 10, registered the disappearance of third oxidation peak (figure 1.7). As seen figure 1.7 oxidaton of thiosulfate ions in acid and alkaline medioum have

big. The oxidation kinetics of sulfur was difficult, so interm oxidation of thiosulfate

ions not only depended on with the presence of thiosulfate ions but also due to close

reaction medium, pH value of the products, disproportion and decomposition reaction

of thiosulfate ions.

25

Figure 1.7 – LSV of 0.5 mol.l-1 of thiosulfate solution at pH=10

1.4 E-pH diagram of sulfuric- water system. A comprehensive survey of the

classical electrochemical facts for sulfur, selenium, and tellurium, as documented until

about 1970, can be found in the reviews of Zhdanov [74], where from we cite the lists

of standard and formal potentials for aqueous solutions, in tables 1.2 many of these

potentials have been calculated thermodynamically since the experimental

determinations are few. The listed data are largely drawn from the monograph by

Pourbaix. In these tables, the redox systems are assorted by decreasing formal valency

of chalcogen in the oxidized state, while at a given valency of the oxidized state they

appear in the order of decreasing valency of sulfur in the reduced state.

Latimer [75] has compiled useful aqueous redox transition potential diagrams that

are convenient as a quick guide in practical problems and for perceiving the oxidation–

reduction properties of some sulfur hydride and sulfur oxide species. Standard

potentials of chalcogens in non-aqueous media are generally not known. As tandard

approach for the theoretical presentation of electrochemical equilibria is the use of

Pourbaix [76], or potential–pH predominance area diagrams, which incorporate

chemical and electrochemical thermodynamics simultaneously in a straight forward

manner. These diagrams comprise an extremely useful, yet fundamental, starting point

for the study of electrochemical systems. Certainly, the ability to predict, understand,

and ultimately control electrochemical reactions requires also knowledge of process

kinetics. Reproduced below are the potential–pH diagrams for the chalcogen–water

systems will serve as a guide to all subsequent discussion on aqueous systems used for

electrochemical preparations of metal chalcogenides. The diagrams represent, almost

exclusively, the important “valencies” of the chalcogens, namely –2, +4, and +6. The

diagrams are valid only in the absence of substances with which the respective

chalcogen can form soluble complexes or insoluble salts.

26

It is considered useful to include here the potential–pH diagram for some redox

systems related to oxygen (figure 1.8) [77].

Table 1.2 – Standard potentials of sulfur in Aqueous solution

Half-reaction Standard or formal potential

(E0, V at 25◦C)

1

2

S2O82− + 2e- → 2SO4

2−

+ 2.01

S2O82- + 2H+ + 2e- → 2HSO4

2−

+2.123

2SO42−+ 4H+ + 2e- > S2O6

2−+ 2H2O

-0.22

SO42− + 4H+ + 2e- — H2SO3 + H2O

+0.17

SO42- + 4H+ + 2e- — SO2 + 2H2O +0.138

SO42-+ H2O + 2e- — SO3

2- + 2OH-

-0.93

HSO42− + 7H+ + 6e- → S(s) + 4H2O

+0.339

SO42- + 8H+ + 6e- → S(s) + 4H2O

+0.357

HSO42- + 9H+ + 8e- → H2S (aq) + 4H2O

+0.289

SO4- + 10H+ + 8e- → H2S (aq) + 4 H2O

+0.303

SO4- + 9H+ + 8e- → HS- +4H2O

+0.252

SO4- + 8H+ + 8e- → S2- + 4H2O

+0.149

SO4- + 10H+ + 8e- → H2S (g) + 4H2O

+0.311

S2O62− + 4H+ + 2e- →2H2SO3

+0.57

S2O62− + 2H+ + 2e- → 2H2SO3

−

+0.455

3H2SO3 + 2e- → S2O62−+ 3H2O

+0.30

2 H2SO3 + H+ + 2e- → HS2O42− + 2H2O -0.08, -0.056

27

Сontinuation table 1.2

1 2

S2O62− + 2e- → 2SO3

2-

+0.026

2SO32-+ 2 H2O + 2e+ → S2O4

2−+ 4 OH-

-1.12

2SO32- + 4H+ + 2e- → S2O4

2− + 2H2O

+0.416

2HSO3- + 3H+ + 2e- → HS2O6

2−+

2H2O

+0.060

2HSO3− + 2H+ + 2e- → S2O4

2− + 2H2O

-0.013, -0.009

4 H2SO3 + 4H+ + 6e- → S4O62− + 6H2O

+0.51

4HSO3− + 8H+ + 6e- → S4O6

2− + 6H2O

+0.581

4SO2(g) + 4H+ + 6e- → S4O62− + 2H2O

+0.510

2 H2SO3 + 2H+ + 4e- → S2O32− + 3H2O

+0.40

2S2O32− + 3H2O + 4e- → S2O3

2−+ 6OH-

-0.58

2 S2O32− + 6H+ + 4e- → S2O3

2− + 3H2O

+0.705

H2SO3 + 2H+ + 2e- → H2SO2 + H2O

< +0.4

2HSO3− + 4H+ + 4e- → S2O3

2− + 3H2O

+0.491

5H2SO3 + 8H+ + 10e- → S5O62−+ 9H2O

+0.41

H2SO3 + 4H+ + 4e- →S(s) + 3H2O

+0.45

SO32- + 3H2O + 4e- → S(s) + 6OH-

-0.66

SO2(g) + 4H+ + 4e- →S(s) + 2H2O +0.451, +0.470

S4O62− + 2e- →2S2O3

2−

+0.08, +0.219, -0.10

S4O62− + 12H+ + 10e- → 4S(s) + 6H2O +0.416

28

Сontinuation table 1.2

1 2

H2SO2 + 2H+ + 2e- → S(s) + 2H2O

>+0.5

S2O32− + 6H+ + 4e- → 2S(s) + 3H2O

+0.465

S5O62− + 12H+ + 10e- → 5S(s) + 6H2O

+0.484

SO(g) + 2H+ + 2e- → S(s) + H2O

+ 1.507

5 S2O32−+30H+ +24e- → 2S5

2- + 15 H2O

+0.331

S2O32− + 8H+ + 8e- → 2HS- + 3H2O

+0.200

S2O32− + 6H+ + 8e- → 2S2- + 3H2O

-0.006

S2Cl2 + 2e- → 2S(s) + 2Cl-

+ 1.23

5S(s) + 2e- → S2-

-0.340, -0.315

4S(s) + 2e- → S42-

-0.33

S(s) + 2H+ + 2e- → H2S(aq)

+0.141

S(s) + 2H+ + 2e- → H2S (g)

+0.171

S(s) + H+ + 2e- → HS-

-0.065

S(s) + H2O + 2e- → HS- + OH- -0.52

S52-- + 5H+ + 8e- → 5HS- +0.003

S52- + 10H+ + 8e- → 5H2S(g)

+0.299

3S42- + 2e- → 4S3

2-

-0.478

S(s) + 2e → S2- A large number of

measurements and calculated

values are available. These vary

from−0.48 to−0.58 V, but most are

closer to−0.48 V

29

Сontinuation table 1.2

1

2

S42- + 2e- → S2- + S3

2-

-0.52

S42- + 4H+ + 6e- → 4HS-

+0.033

2S32- + 2e- → 3S2

2-

-0.506

S32-+ 2e- → S2- + S2

2-

-0.49

S32- + 3H+ + 4e- →3HS-

+0.097

S22- + 2e- → 2S2-

-0.48, -0.524

S22− + 2H+ + 2e- → 2HS-

+0.298

30

Figure 1.8 – Potential–pH diagram for the stable equilibria of the system sulfur–

water at 25◦C

HS-, S2-, S, HSO4− , SO4

2− and S2O82−, which contain sulfur only in the oxidation

states –2 and +6 (aside from the solid element); other species, such as thiosulfates,

dithionites, sulfites, and polythionates arei n “false” equilibrium in aqueous solution.

Note also that the persulfates (S2O82−) are unstable in water, so that if the equilibria

were attained, only the remaining six forms would be present in solution. The limits of

the domains of relative predominance of the dissolved substances included in the

Pourbaix diagram (plus solid sulfur) regard the following homogeneous and

31

heterogeneous (solid/liquid, gas/liquid) equilibria, involving redox and non-redox

processes:

Limits of the domains

of relative predominance of

dissolved substances

(1’) H2S/HS-

(2') HS-/S2-

(52’) H2S(g)/H2S(aq)

(53’) H2S (g)/HS-

(11') HSO-4 /SO2-

redox equilibrium

(41') S2O82− + 2e- → 2SO4

2−

(40') S2O82− + 2H+ + 2e- → 2HSO4

−

(50') 2HSO4−+ 7H+ + 6e- → S(s) + 4H2O

(51’) SO42− + 8H+ + 6e- → S(s) + 4H2O

(20’) HSO4- + 9H+ + 8e- → H2S(aq) + 4H2O

(21’) SO42−+ 10H+ + 8e- → H2S (aq) + 4H2O

(22') SO42− + 9H+ + 8e- → HS- + 4H2O

(23') SO42− + 8H+ + 8e- → S2- + 4H2O

(58') SO42− + 10H+ + 8e → H2S (g) + 4H2O

(42') S(s) + 2H+ + 2e- → H2S (aq)

(60) S(s) + 2H + 2e- → H2S (g)

(43’) S(s) + H+ + 2e- → HS-

Solid substances considered: S (sulfur, light yellow, orthorhombic). Dissolved (in

aquo) sulfur substances considered: H2S (hydrogen sulfide, colorless), HS- (hydrogen

sulfide ion, colorless), S2- (sulfide ion, colorless), S22− (disulfide ion, orange), 𝑆3

2−

(trisulfide ion, orange), S42− (tetrasulfide ion, orange), S5

2− (pentasulfide ion, orange),

H2S2O3 (thiosulfuric acid, colorless), HS2O3− (acid thiosulfate ion, colorless), S2O3

2−

(thiosulfate ion, colorless), S5O62− (pentathionate ion, colorless), S4O6

2− (tetrathionate

ion, colorless), HS2O4−(acid dithionite ion, colorless), S2O4

2− (dithionite ion, colorless),

S3O62− (trithionate ion, colorless), H2SO3 (sulfurous acid, colorless), HSO3

− (bisulfite

ion, colorless), SO32− (sulfite ion, colorless), S2O6

2− (dithionate ion, colorless), H2SO4

(sulfuric acid,colorless), HSO4− (bisulfate ion,colorless), SO4

2− (sulfate ion, colorless),

S2O82− (dipersulfate ion, colorless).

32

1.5 Sulfur content Oil and sulfur-containing waste sources impact on the

environment

At the present time, one of the main issues – suspension of environments’

exposure consequences with painful disasters. For instance, prevention of the

environment and efficient application of natural resources is very important. As well

as, one of the main causes of environmental pollution is the rapid development of

industries, as a result of their actions, the recovery of natural cyclicity ability is

seriously affected. Any industry have technogenic impact on our environment. One of

the examples is oil production that is considered the main source of income of the

country economy [78].

Among the 55 oil-producing countries in the world the Republic of Kazakhstan is

placed on the 12th according to the hydrocarbon reserves. The volume of oil produced

in our country includes one of the seventeen all oil, which produced in the CIS.

However, depending on geological features, our country’s oil is deemed medium and

high sulfur containing oil. That is why, during the cleaning process of hydrogen sulfide

from crude oil, elementary sulfur is formed as an additional product and is accumulated

as a waste in the territory of production. These chemicals lead to eyes and inflammation

of the mucous of upper respiratory tract, diseases of skin and other gastrointestinal tract

also causes irritation, moreover, sulfur is not stored in the air. The famous scientist,

academician, same researcher believed that sulfur is meteorological and under the

influence of temporary factors which cracked by erosion and further only accelerated

the destruction process. By the way, a large amount of hydrogen sulfide, sulfur dioxide

and polysulfide is allocated and has ecological negative impact to the environment.

It is known that, organic and inorganic compounds of sulfur are always present in

all living organisms. It is an important biogenic element, but according to the negative

impact on the environment and human sulfur and its compounds are on the first places.

Thus about 96% of sulfur emitted from enterprises, release into the atmosphere as

sulfur dioxide SO2. In the atmosphere, sulfur dioxide reacts with water vapor and

formes acid solution, which then falls as acid rain. Once in the soil, acidic water inhibits

development of soil fauna and plants [79].

Among other anthropogenic emissions there are many toxic sulfur compounds and

from them it is necessary to note that inhalation of hydrogen sulfide causes rapid

dulling of reactions to its unpleasant odor and can lead to serious poisoning, even with

fatal consequences. MPC hydrogen sulfide in the air of working premises 10 mg/m3,

in the atmosphere 0.008 mg/m3. The toxic properties of sulfur and its some compounds

are listed in table 1.3 [80].

Table 1.3 – The toxic properties of sulfur and its compounds

Toxic effects compounds MPC, mg/m3

MPC (Dust 8 hours a day) S 2,0

MPC (8 hours a day) H2S 10

Irritation of the eyes and nose H2S 4

Mortally for 1 - 3 hours H2S 800

MPC (Dust 8 hours a day) SO2 10

33

Сontinuation table 1.3

1 2 3

Perception threshold SO2 3

Irritation of the eyes and nose SO2 20-50

Mortally for 1 - 3 hours SO2 5000

In the development of oil fields that contains sulfur, waste pollution of the

environment is happening. The presence of sulfur in commercial oil is forbidden

because, it is a catalyst poison, in addition, sulfur compounds, present in petroleum,

dramatically deteriorate operational qualities of fuels and oils and cause corrosion of

equipment.

Maximum allowable concentration of sulfur compounds in soil and permissible

levels of their content on the hazard indicators are shown in the table 1.4 [81].

Table 1.4 – MPC of sulfur compounds (mg/kg) in soil and permissible levels of their

content on the indicators of harmfulness

Substance MPC, mg/kg

soil

considered

background

indicators of harmfulness

translocation

(accumulatio

n in plants),

mg/kg

migratory general -

sanitary,

mg/kg aqueous,

mg/kg

airy,

mg/kg

The total content

Hydrogen

sulfide

0.4 160.0 140.0 0.4 160.0

Elemental

sulfur

160.0 180.0 380.0 - 160.0

Sulfuric

acid

160.0 180.0

380.0 - 160.0

Main formation source of sulfur – the burning of fuels and production of metals

generalization from sulfur ore. On the basis of these enterprises, a large amount of

sulfur oxides spreads in the air. Sulfur oxides in the biosphere mixed with various forms

of natural sulfur sources.

As well as non-ferrous metallurgy industry, oil refining, synthesis of inorganic

and organic substances and more the field of industries the diversity of the nature of

pollutants released into the atmosphere was shown in table 1.5.

The composition of the waste from the productions released into the air varies, they

contain hundreds of gases and chemical compounds that can be in the form of vapors

and aerosols.

34

Table 1.5 – The nature of the air pollutants in the field of chemistry

Produced substance The composition of the air pollution

Sulfuric acid

NO, NO2, SO2, SO3, H2SO4

SO2, SO3, H2SO4

The method of nitrous NH3, (NH (SO3NH4)2, H2SO4

Contact method H2SO4, HF

Sulfa Amin acid H2S, Cl2, SO2, (CH3)2S

Superphosphate SO2, H2S, P2O5, karbofos dust

The main sources of sulfur and its compounds from the environment shown that

oil, petrochemistry and chemical enterprises and among the sulfur compounds the

hydrogen sulfide provided the effect to the environment. Especially, hydrogen sulfide’s

impact on the environment causes significant changes in the nature every day and it is

shown that it disturbs factor of the equilibrium and structure of geological system

metabolism.

That is why, it is very important to create simple methods to obtain necessary

sulfur’s different compounds and that is one of the most topical issues.

It is well known from the literature, in earlier times, elemental sulfur was

considered as one of the basic chemical raw material in the manufacturing industry

and the national economy than- coal, oil, lime, salt and at the present time in chemical

industry it is widely used for the production of sulfuric acid [82].

35

2 EXPERIMENTAL METHODS AND IMPLEMENTATION OF

TECHNOLOGY

2.1 Methods of potentiodynamic polarization curves recording

Electrochemical oxidation-reduction in aquoues solution was investigated by

recording polarization curves under potentiodinamic regime and electrolysis under

galvanostatic conditions.

To recording potentiodynamic polarization curves was used "Autolab"

potentiostat brands of PGSTAT 302N. "Autolab" potentiostat / galvanostat carried out

three electrode cell glasses with thermostat (figure 2.1), which is known to be applied

for corrosion studies, bio-electrochemistry, in the study of rechargeable batteries and

many other areas. External manifestations of potentiostat was shown in figure 2.1. The

surface of the instrument panelwas placed cell for working, counter and reference

electrode. With (U, E, I) signs marked additional cell is used to identify the relationship

of the device with potentiostat. The central cell of the surface panel devoted to check

the device (determined by C + R and W) and these cells are not applied for

electrochemical measurement. While working left side of surface of panel, red or green

diodes indicates the working status of the device.

Back of panel is located cell which separates and connects the device that

connected to the network cell and zero model is connected to the cable and computer

and potentiostat is connectted with each other. At the same time, back of planes is

located air-cooled radiator. Management of device is fully implemented by a private

computer program. Calibration was carried out once a month.

Before working, potentiostat was connected to the mains during the 20-30

minutes. When the potentiostat is ready to work, electrodes are immersed in a cell

where filled with electrolyte then electrochemical measurements are carried out.

Device management and all functions of processing of the measurement results

selected at the beginning of the program.

As a working electrode rhodium (S = 0.04 cm2) is used, which placed on the

conductive fluoroplastic (figure 2.2). As comparative electrode used silver chloride

(E0= +0.203 V) and as auxiliary electrode served platinum electrode. Potential values

are comparable with silver chloride electrode.

Before each practice electrodes always smoothed microns emery paper, then

washed with distilled water, implemented through wiping with a filter paper. The

potential of the working electrode measured by maximum close placing on surface of

lugine capillaries.

36

1 - "Autolab" potentiostat; 2 - electrochemical cell; 3 – working electrode (Rd);

4 – reference electrode(silver chloride); 5- platinum electrode (counter electrode); 6

– bridge

Figure 2.2 – General view of potentiodynamic polarization curves recording

installations

37

Before the cell experiment is washed by a large amount of water, distilled water

after that washed with working solution.

Before each experiment installations according to the operational objectives

were prepared for the work.

Figure 2.2 – Construction of rhodium electrode for unloading polarization

curves

In many cases, during the electrochemical reactions, the nature of the electrode

polarization determined by studying the effect of temperature on the rate of

electrochemical reactions [83]. The effect of temperature on the rate of electrochemical

process calculated by similar to the equation of Arrhenius:

lgi = B - A

2.3RT (2.1)

Where: i - the current density; B - constant; A- effective activation energy.

Activation energy of the electrochemical reaction calculated by a straight-line

figure lgi-1/T depends on the value of the angular coefficient.

2.2 Preparation of current conductor sulfuric-graphite composite electrodes

and methodology of electrolysis

Electrochemical studies was carried out with a glass electrolyzer in galvanostatic

condition. Installations for the study electrochemical properties of elemental sulfur in

different solutions and principal schemes to receive sulfate compound with anodic

polarized sulfur-graphite composite electrode (which processed by sulfur waste) were

shown on figure 2.3 and 2.6.

The manufacturing method for sulfur and graphite or sulfur composite electrodes

are as follows:

Preliminary graphite and sulfur ground up to 25-50 mcm (figure 2.4). These

powders used for the preparation of electrodes (50% of graphite powder, 50% of sulfur

powder,). For this, in advance 1:1 ratio measured graphite and sulfur granules were

38

powdered individual in a special container, then first, sulfur powder on the electrical

heating stove in the fume hoods at 120-130 °C melted by heating then put graphite

powder on the top of melted sulfur and mixed thoroughly, the end this obtained mixture

poured special normalization and cooled at room temperature for 24 hour [84].

1- Sulfur graphite electrode, 2-cation membrane, 3- graphite rod

Figure 2.3 – The principal technological scheme to obtaining sulfur compounds

based on the processing of waste sulfuric

Sulfur-graphite composite electrode could create a different form (plate cylinder).

Developed electrodes with this proposed method, electrolysis can be carried out

50-300 A/m2 current density. During electrolysis sulfur accompanied by

electrochemical way then held to the solution and graphite particles precipitated the

bottom of the electrolyzer. As a result, sulfur and graphite electrode surface is updated.

Deposited graphite powders collected and washed which can be used for against

preparation of the electrode after dried.

We proposed method of preparation of sulfuric graphite electrodes has following

features:

- the technology of manufacturing of sulfur-graphite electrodes is very simple;

- the electrode will be prepared under atmospheric conditions;

- sulfur - graphite electrodes shows very high electrochemical activity;

- electrodes could be made in laboratory conditions without using special,

complex installations;

39

- deposited graphite powder again can be used for the preparation of sulfur-

graphite composite electrode that is why consumption of graphite not much;

Graphite piece, crumbs are industrial waste. Such waste widely used for the

preparation of sulfur-graphite composite electrode. From the literature well known coal

didn’t conduct electricity and some types will be conducted a very small amount. But

graphite is a good conductor. In our research during the perperation of sulfur-graphite

composite electrode carried out comperehernsively study shown instade of graphite

can use its crumbs. And such a waste source in our republic enough. Already from

Temirtau city productions produced a large amount graphite crumbs collected with out

finding application.

In this study used sulfur-graphite composite electrode method’s novelty was

protected innovation patent of RK (№ 21327) [85].

Experiment carried out electrolyzer (1) with a capacity of 200 where allocated by

MK-40 (4) cation membrane (figure 2.6). Electrode polarization (2-3) during electrolysis

is connected to current power (7). In electrochemical chain, in order to regulate and

measurement of the current strength to chain connected ammeter (6), rheostat (5) and key

(8).

Depending on the conditions of the electrolysis sulfur and graphite electrodes could

be polarized as anodic and cathodic. As an additional electrode was used pure graphite rod

or titanium.

By special method prepared composite sulfur graphite electrode’s micrograph was

shown in figure 2.5. Pictures were taken by METHAN-1 micrographical MFN-12

microscope. Obtained micrograph of the surface of the composite sulfur-graphite

electrode, shows that the sulfur and graphite is uniformly distributed by forming a

homogeneous mass on the electrode surface.

Figure 2.4 – Manufacturing of sulfur-graphite composite electrodes

40

(a)

(b)

Figure 2.5 – A micrograph of the composite sulfur-graphite electrode increase (a)

100 and (b) 200 times

41

1 -Electrolyzer; 2- cathode; 3 - the anode; 4 - MK-40 cation membrane;

5 rheostat; 6 - ampermeter; 7 - power supply; 8 - key

Figure 2.6 – Installation for study electrochemical properties of elemental sulfur in

aqueous solution

2.3 Used reagents, drugs and analysis of the obtained products As a result of the electrolysis obtained products were used physico-chemical and

chemical methods. In this work, for analysis iodometry, chelatometry and potentiometric

methods were applied. After the electrolysis formed products: sulfide-, polysulfide-,

sulfate-ions and thiosulfate-ion analysis defined by titration and chelatometry methods

[86-92].

Determing sulfide-, sulfite- and thiosulfate- ions all together in waste water, first of

all sulfide ions deposited in the form of ZnS, CdS by zinc or cadmium salts. To avoid

tanning of sulfite ions with oxygen in the air added glycerol to the solution. In order to

determine sulfide-, sulfite-, thiosulfate-ions, sulfide ions precipitate by adding a solution of

zinc carbonate and cadmium carbonate suspension. This sediment filtered and washed.

The filter paper with a sediment pure into the 250 ml conical flask then 25-50 ml of

0.01 N iodine solution and to create an acidic medium dilute hydrochloric acid were added.

The filter paper is grinded glass rod. After that, excessive amounts of iodine in the

presence of starch titrated 0.01 N sodium thiosulfate solution.

Obtained sulfur compounds by electrochemical way was identified with X-ray and

physical-chemical methods. X-ray studies was taken in DRON-4 diffractometer. As a

42

result of the electrolysis formed product’s current output calculated by the following

formula:

ƞ =𝑚𝑡ℎ𝑒𝑜𝑟

𝑚𝑝𝑟𝑎𝑐𝑡 100% (2.2)

There:

mtheor ˗ practical weight of formed substance during carrying out the certain the size

of the electric current, g;

mpract - product theoretical weight which calculated by Faraday's law, g

In order to determine current output, theoretical weight substances calculated by

Faraday's law:

Mtheor = Iqτ (2.3)

where: I - current, A; q- electrochemical equivalent, g .A/ hr; t- time, hours.

q = (2.4)

where:

A - the atomic mass of the element; n - the corresponding valence of the element;

F - Faraday number.

All obtained experimental values were processed by mathematical statistics

method [89]. To make sure the accuracy of the experiment results which were repeated

at least 3-4 times.

2.4 determination of sulfur-containing compounds by physico-chemical

methods

As a result of the electrolysis, sulfur ions are formed during the analysis is

conducted. Sulfide- and polysulfide- ions were identified by [86-92] given method.

Sulfide ions with zinc and cadmium salts were infused as ZnS and CdS. By adding a

solution of glycerin (to prevent oxidation of ions with the oxygen in the air) tincture of

sulfide filtered. Sulfide ions in the tincture were identified by iodometric method.

In order to determine sulfide and polysulfide ions in 250 ml conical flask was poured

50-100ml preliminary neutralized testing solution. Then added 10ml of glycerol and

up to 150ml diluted with distilled water. After that 20ml of zinc carbonate suspension

added and filtered. Filtered sediment washed with hot water, in 200 ml volumetric

measuring flask filtrate cooled and diluted with distilled water

2.4.1 Determination of ions– sulfide, sulfite, sulfate, thiosulfate and polysulfide

Determination of sulfide ions. Sulfide ions were identified by the iodometric

method. The analysis is carried out for the following reaction:

:

43

S2- + I2 → 2I- + S↓ (2.5)

In 250 ml flask cone put the sediment filter and 25-50 ml a solution of iodine

added then acided 5ml hydrochloric acid with the ratio of 1:9. With the glass stick by

mixing filter excessive amounts of iodine, in the presence of 0.5% starch titrated with

0.01 N of sodium thiosulfate.

Amount of sulfide ions (x), mg / l will be found by the following formula:

X =(ak1−bk2)∙16,03∙0,01∙1000

𝑉 (2.6)

There:

A- the amount of added iodine solution, ml;

k1 – correction coefficient that applied to the concentration of 0.01N iodine

solution;

k2 – correction coefficient that used to the concentration of 0.01N thiosulfate

solution;

b - exploded volume of 0.01N sodium thiosulfate solution for titration process,

ml;

V - the amount of testing electrolyte, ml; 16.03 – for 1ml 0.01N iodine solution

calculated sulfide ions equivalent size.

On direct current dissolution process of sulfur electrode with the formation of

sulfide and polysulfide ions accompanied by the following reaction:

S0 + 2e S2- (2.7)

nS + 2e S𝑛2− (2.8)

Identification of thiosulfate ions. Took a certain number of aliquots from

allocated filtrate to 250 ml cone-shaped flask over the top added 5 ml 40% of

formaldehyde and 10 ml 10% of acetic acid, thiosulfate ions titrated with 0,01N iodine

solution in the presence of 1-2 ml 0.5% of starch until the color of solution changed to

blue. Used the amount of iodine for the titration accordance with the amount of

thiosulfate. So the amount of thiosulfate is determined by the following reaction:

Na2Sn+1 + nNa2SO3 → Na2S + nNa2SO23 (2.9)

НСНО +SO32−+ Н+ → СН2ОН SO3

2− (2.10)

2S2O32−+ I2 → 2I- + S4 (2.11)

Amount of thiosulfate ions (x), mg / l will be found by the following formula:

X=ak∙200∙0,01∙112,1∙1000

V V1 (2.12)

There:

44

а – the amount of iodine for the titration, ml;

k – correction coefficient that applied to the concentration of 0.01N iodine

solution;

V – the amount of electrolyte for analysis, ml;

V1 – the amount of an aliquot, ml;

200 – volume of flasks, ml;

0.01 – normal concentration of the titration solution;

112.1 – for 1ml 0.01N iodine solution calculated thiosulfate ions equivalent size.

Definition of polysulfide ions. In order to determine polysulfide ions the testing

solution is heated 10 minutes up to 50-60 °C in the presence of sulfite.

Interaction reaction of polysulfide with SO32− ions:

S𝑛2− + (n-1) SO3

2− So + (n+1)S2O32− (2.13)

After that according to the above-mentioned method sulfides will be separated in

the form of zinc sulfide. To filtrate added 5 ml of 40% formaldehyde ( to associate with

sulfite ions) and 10 ml 10% of acetic acid, the thiosulfate ions titrated with iodine

solution, in the presence of 1-2 ml of 0.5% starch until color of solution changed to

blue.

Determination of sulfite ions. To 250 ml volume cone-shaped flask add a certain

volume of (25-50ml) iodine solution then poured 5-10 ml 10% of acetic acid and the

amount of the sulfide separated filtrate, top of them insert 1-2 ml of starch solution then

titrated with 0.01 N solution of sodium thiosulfate. Spent the amount of iodine for

titration process corresponds to the total size of S- and S2O32− ions in the solution.

Oxidation process of SO32− - ions carried out by following reaction:

SO32− + H2O + I2 SO4

2− + 2H+ + 2I- (2.14)

Amount of sulfite ions (x), mg/l will be found by the following formula:

X=(bk1−ck2−ak1)200∙40,03∙1000

V V1 (2.15)

There:

а - the volume of 0.01 N iodine solution for the determination of sulfite ions, ml;

b – the volume of 0.01 N iodine solution added for analysis, ml;

с –the volume of sodium thiosulfate solution used for reverse titration, ml;

k1 - correction coefficient that applied to the concentration of 0.01N iodine

solution;

k2 - correction coefficient that applied to the concentration of 0.01N sodium

thiosulfate solution;

V – the studied solution volume, ml;

45

V1– the volume of aliquot to determine the solution was cleaned from the filter,

ml; 200 - the volume of flask, ml; 40.03- equivalent of sulfite.

Determination of sulfate ions. To take 5 - 25 mg SO42− ions conained aliquot,

poured into the 250 ml conical flask, and diluted with distilled water up to 100 ml. To

this solution added 2 ml of hydrochloric acid with ratio of 1: 1 then heated, over them

poured 3ml hot BaCl2 solution, mixed for one minute and heated for an hour until it

boils. Obtained sediment is carried out the filtration washed carefully with distilled

water, then dried and burned in the temperature of 800 °С. The received product have

measured, according to differences weight of BaSO4 have found.

Amount of sulfate ions (x), mg/l will be found by the following formula:

X=m∙0,4116∙1000

48,03 𝑉 (2.16)

There:

m - mass of BaSO4, mg;

V – The volume of sample is taken for analysis, ml;

0.4116 - BaSO4 's coefficient is calculated the ions of SO42− ;

48.03 – equivalent of SO42−ions.

2.4.2 Determining of the concentration of sulfide ions by the application of

ionomer

While studying electrochemical properetis of elemental sulfur in aqueous

solution, after electrolysis obtained polysulfide ions concentration on the cathodic side

was identified by the method of ion selective electrode [93].

Ionomers laboratory I-160MI intended for measurement indicator of the activity

of hydrogen ions (pH), and other monovalent and divalent cation ions (pX), as well as

mass, molar concentration and the mass fraction of ions (cX), redox potential

(Eh),electromotive force (EMF) of the electrode system and the temperature of aqueous

solutions.

In the measurement of cation activity in the solution and its redox potential were

used electrode system composed of detective and auxiliar electrode. The potential of

the measuring electrode depends on the content of specific form of ions in solution,

called potential generators. The potential of the reference electrode is not dependent on

the composition of the solution and it serves as a reference when measuring the

electromotive force (EMF) and developed electrode system.

The measurement results in terms of concentration cX (for all ions except H+)

depending on the selected dimension is determined by the formulas of 2.17-2.19:

cX = (10-рХ) К, (2.17)

Where, cX - concentration, mol/l; K - activity coefficient. Depending on the ionic

strength of the sample solution. On the device of I-160MI K- is assumed to be 1.

46

cX’ = М (10-рХ) К, (2.18)

Where cX '- concentration, g/l; M - molar mass of the ion, g/mol;

cX’’ = (10-рХ) К/|n|, (2.19)

Where cX '' – concentration, mol equivalents / liter; n - ion charge.

Monovalent cations, including H+, n=1;

Monovalent anions, n = - 1;

Divalent cations, n = 2;

Divalent anions, n= - 2;

15 minutes before the useing of the installation should be turn on and need to

prepare practice. In order to turn off facility need to print "off" button for 1-2 seconds.

The amount of the product formed on the cathodic side determined by ion-

selective electrodes [94, 95]. Mentioned electrode based on the definition of certain

amount of ion concentration, identified each ion has a special electrodes, corresponding

electrode to the each ion is considered selective. The range of possibilities of

determining the amount of the ion is very wide. Which in the range of 10-5-10-1 mol/l,

very simple and fast, in this work ionomer’s type model of I-160 MI used.

47

1-Determining electrode (sulfide- ion selective electrode- xc-sgl.-001, 02-58);

2- auxiliary electrode (electrode-AgCI which filled with 0.3 M KCI); 3-thermo

sensor TDL-1000; 4-bridges; 5-beaker; 6- the testing solution (containing sulfide

ions); 7-ionomer

Figure 2.7 – Installation for the determination of the amount of sulfide ions by

using ion-selective electrodes

2.4.3 Used reagent and the identification of chemical compounds

The following reagents were used in our research works: elemental sulfur

according to the name of "clean", graphite powder (25.0 microns) according to the

name of "pure for analysis"; hydrochloric acid (p = 1.19 g/cm3), 10% acetic acid (p =

1.07 g/cm3), sodium hydroxide, sodium carbonate, sodium sulphite, zinc sulfate, zinc

acetate, 0.1 N iodine fiksanaly, sodium thiosulfate fiksanaly, 40% formaldehyde,

glycerol, starch, filter paper (blue ribbon). Bidistilled water used to prepare solutions.

In order to determine obtained products as a result of the electrolysis chemical

and physico-chemical (X-ray, microscopes, IR spectrum), chemical analysis methods

and equipment were used.

48

3 ELECTROCHEMICAL PROPERTIES OF ANODE POLARIZED

SULFUR ELECTRODE’S IN THE SOLUTION OF HYDROCHLORIC ACID

Oil production in the Republic of Kazakhstan mainly developed in the western region

of country – Mangistau, Atyrau, west Kazakhstan and Aktobe, as well as Kyzylorda

regions which is located the southern of country. And produced oil composition directly

related to the geological features of the fields [96], Kazakhstan oil and gas is rich in

hydrogen sulfide (H2S), which is removed as elemental sulfur during the production

process. As a result, huge quantities of by-product sulfur are produced and stored in

large stockpiles. According to the data, at the Kashagan Field by the processing of

crude oil, every year million ton of sulfur may be collected into the environment. At

the same time, has an information that during the processing of crude oil for many

years, approximately 12 million tons of sulfur was accumulated at the Tengiz field.

In the last, this accumulated sulfur in the country have been sold to foreign

countries by very cheap price. Sulphur international experts noted that Kazakhstan is

among the 10 largest exporters of sulphur. Processing of sulfur and obtaining its

compounds by certain technologies was not implemented because of that is

economically inefficient. To resolve this problem, today’s one of the key issue is to

create new methods for processing of elementary sulfur and getting its usefull

compounds [97]. That is why, in order to obtaining a variety of sulfur compounds there

hardship is arisesed in comprehensive study its electrochemical properties. Elemental

sulfur is isolator and insoluble in water and acid. Therefore, its electrochemical

properties in aqueous medium are very poorly studied [98].

previous results of experimental studies identified that electric conductive sulfur

electrode, in practice at room temperature in aqueous solutions didn’t insoluble if

electrode unpolarized condition.

Electrolysis was hold in electrolytic cell with capacity of 200 mL where the space

of electrode was allocated with MK-40 cationite membrane. As a anodic and cathodic

electrode were used 70 cm2 sulfur-graphite and 64.5 cm2 graphite electrode. Electric

conducted sulfur-containing composite electrode developed with a special method

which provided by ourselves.

The research work carried out the laboratory of "Electrochemical Technologies"

at “Institute of Fuel, Catalysis and Electrochemistry after named D.V. Sokolsky” as a

continuation of [99-108] the scientific papers in the field of investigation of the

electrochemical properties of elemental sulfur.

For the main research, 50 g/l of НCI solution was used as an electrolyte. The

amount of sulfate ions from electrolysis was determined by quantitative analysis

method [109].

The main factor to influenced for the reactions direction and speed which carried

out on the electrode – current density. That is why, influence of current density for the

formation of sulfate ions was investigated in the range of 50-250 А/m2 at room

temperature, in 50g/l hydrochloric acid solution.

During the electrolysis on the anodic side sulfur could oxidized sulfite and sulfate

ions.

49

S + 3H2O – 4е → SO32− + 4Н+ E0 = +0.450 V (3.1)

S + 4H2O – 6е → SO42− + 8Н+ E0 = +0.359 V (3.2)

2Cl-(aq) - 2e → Cl2(g) E0 =+1.359V (3.3)

At the time of electrolysis on the cathode occurs discharge of hydrogen ions:

2Н+ + 2e− = H2 E0 = 0.0V (3.4)

С(НCl) = 50 g/l; t = 1,0 hour; T = 25 ºС

Figure 3.1– The influence of current density in anodic polarized sulfur-graphite

composite electrode to formation of sulfate ions current efficiency

As seen in Figure 3.1, the formation of sulfate ions current efficiency by the

increasing of current density decreased gradually. This can be explained additional

process – due to the increase in the proportion of chloride ions discharge. This procces

speeds quicker than complicated oxidation process of sulfur,that is why main oxidation

output reduce due to the separation of chlorine gaz.

Following research, the concentration of HCl for the formation of sulfate ions

current efficiency was investigated. In this stage, according to the previous results 50

A/m2 was chosen as optimal current density.

Figure 3.2- shows, by the increasing of the concentration of HCl identified that

the formation of sulfate ions current efficiency was raised gradually. Apparently, an

increase of the concentration chloride ions could increased sulfur’s activity which

allows to conclude that the opportunity of the oxidation process of sulfur atoms was

given by chlorine:

S + 3Cl2 +4H2O → H2SO4 + 6HCl (3.5)

50

As well as, by using the optimal values in this experiments, influence of

electrolysis duration (0.25-1.5 hours) for the formation of sulfate ions current

efficiency was investigated (figure 3.3).

The anodic polarized sulfur-graphite electrode oxidation process with presence of

sulfate ions higher current efficiency was appeared start time of electrolysis. This

phenomenon can be assumed that electrolysis products sulfate ions diffusion limitation.

Diffusion is the net movement of molecules or atoms from a region of high

concentration (or high chemical potential) to a region of low concentration (or low

chemical potential). Which is depnde on time, and illustrated that on the initial time of

oxidation procces given the high current efficiency of sulfate ions, and by the

increasing of electrolysis duration the formed sulfate ions mass transported lower

concentration region, as a resulte reduced the number of molecules to react.

I = 50A/m2; t = 1 hr; T = 25ºС

Figure 3.2 – The influence of HCl concentrations to formation of sulfate ions

current output by anodic polarized composite sulfur-graphite electrode

51

I= 50 А/m2; С (НCl) = 110 g/l; T = 25 ºС

Figure 3.3 – The influence of electrolysis duration in anodic polarized sulfur-

graphite composite electrode to formation of sulfate ions current efficiency

Conclusion of section 3

In conclusion, at the anodic polarization were identified that, in HCl solution

sulfur which consisted in electrical conducted composite electrode could oxidized with

high current output by formation of sulfate ions. The influence of different parameters

(the current density, the concentration of hydrochloric acid, the duration of electrolysis)

for electrochemical behaviour of sulfur-graphite electrode were shown at optimal

condition sulfate ions formation current output was 41.5%.

By the increasing of chloride ions amount in the solution that leads growth of

activation for the oxidation of anodic polarized sulfur.

The results of the study – can serve as the basis for make new ways to obtaining

sulfur compounds that widely used in the national economy.

52

4 ELECTROCHEMICAL PROPERTY OF SULFUR IN SODIUM

CHLORIDE AND CARBONATE SOLUTION

4.1 Dissolution of anodic polarized elemental sulfur in sodium chloride solution

At present, by the developing of oil production, the problem of environmental

pollution by industrial waste has been increased. In Kazakhstan, the amount of sulfur in

the oil is higher than other oil-producing countries [110]. Therefore, in the processing of

oil and oil products one of the main waste is –sulfur.

If left unresolved, the potential environmental and economic liabilities associated

with the stored sulfur will pose an increasing risk for the international oil & gas oil

companies operating in Kazakhstan.

Ability to understand the different properties of sulfur, which is considered one

of the chalcogen will help in creation of its electrochemical technology [111].

Data about electrochemical properties of various sulfur compounds were shown

on the researcher’s scientific works and monographs and reviewed in systematic basis

were given in a lot of scientific data [76,117]. But, detailed information about

electrochemical properties of elemental sulfur wasn’t exist. As well as, now concluded

that sulfur with low active could not melt under the influence of an electric shock,

because this element is a dielectric and do not conducted the electrical current. But it

has been well known since ancient times that under the influence of an electric current

could dissolve many metals and obtainment of their compounds. The dissolution of the

sulfur in aqueous solutions comprehensively studied with prepare of a sulfur-

containing composite electrode by using this method for sulfur.

Moreover, this study as the electrode material specially prepared conductive

composite sulfur electrode used too.

As well as, current conductor composite sulfur electrode gives electrochemical

activity to dielectric sulfur. By anodic polarization of sulfur electrode shown that the

possibility to get sulfate compounds which is one of the most useful compounds of

sulfur.

During the research, the influence of various parameters for the anodic polarized

sulfur-graphite composite electrode’s oxidation with formation of sulfate ions in NaCl

aqueous solution ( current density, NaCl concentration solution, electrolysis duration)

were studied and the optimal condition for the formation of sulfate ions was

investigated.

The effect on the generation of sulfate ions on the anodic current density was

carried out in the range of 50-250 A/m2 at room temperature in 50 g/l NaCl solution

(figure 4.1).

The highest current efficiency of sulfate ions was shown on lower current density

(50-100 А/m2), and by the increasing of current density to 250 А/m2, which is

decreased current output gradually. A decrease in current yield is due to additional

process. It depends charging of these hydroxyl ions with the formation of oxygen.

During electrolysis the following reactions may occur on the the anode:

S + 6OH- -4e → SO32− + 3H2O E0 = -0.660 V (4.1)

53

S + 8OH- -6e → + 4H2O E0 = -0.753 V (4.2)

2Н2О -4е → О2+4Н+ (4.3)

And formed chloride gaz:

2Cl- -2e → Cl2 (4.4)

On the cathode occurs separation of hydrogen and reduction of sulfur process:

nS +2e→S𝑛2−… nS2- (4.5)

2Н2О +2е → H2+2OН- (4.6)

С(NaCl) = 50 g/l; t = 1,0 hour; T = 25 ºС

Figure 4.1– The influence of current density in anodic polarized sulfur-graphite

composite electrode to formation of sulfate ions current efficiency

When current density on the sulfur electrode was 50 A/m2, the current yield

generation of sulfate ions indicated 48% and at 250 A/m2 current density equal to

12.5%. The reduction of formed sulfate ions curren output in the increasing of current

density on the electrode explained by the generation of additional process oxygen gaz.

Following study, the concentration of NaCl for the formation of sulfate ions

current efficiency was researched. This research stage based on the results of the past

analysis as optimal current density of 50 A/m2 was chosen. As seen from figure 4.2

54

identified that the increase in the concentration of NaCl solution, there was a step rise

in the formation of sulfate ions current output. Oxidation of sulfur with the formation

of SO42− ions exceed 100% current yield accompanied can be interpreted as the reaction

of sulfur’s disproportion (equation 1.25).

Disproportion reaction usually carried out in alkaline solution which well known.

Apparently, this reaction can take place in NaCl solution too. According to this reaction

formed sulfite ions on the anode oxidized by giving one electrode which creates an

opportunity to increase the current yield.

J = 50A/m2; t = 1 hour; T = 25ºС

Figure 4.2–The influence of NaCl concentrations to formation of sulfate ions

current output by anodic polarized composite sulfur-graphite electrode

With the increasing of the concentration of sodium chloride the current output in

the formation of sulfate ions soared. Based on the achieved data, the following research

as the most effective concentration of NaCl 150 g/l were selected.

The effect of the electrolysis of duration for the formation of sulphate ions current

efficiency shown in figure 4.3.

The anodic polarized sulfur-graphite electrode oxidation process with formation

of sulfate ions higest current output was appeared initial time of electrolysis.

55

I= 50 А/m2; С (NaCl) = 150 g/l; T = 25 ºС

Figure 4.3–The influence of electrolysis duration in anodic polarized sulfur-

graphite composite electrode to formation of sulfate ions current efficiency

4.2 Electrochemical properties of dissolution elemental sulfur by formation

of sulfate-ions in sodium carbonate solution

At the present time, with the increase in oil production causes a lot of

environmental problems. In other words, oil processed in the country have a sulfur, for

example fuel (gasoline, solaria) compliance with the sulfur compounds which exposure

to engine corrosion and will have a material impact on the destruction of the

environment [112-113]. Preliminary studies, shows that anodic polarized conductive

composite sulfur electrode in sodium carbonate solution melted intensively with the

formation of sulfite and sulfate ions.

Electrolysis carried out under galvanostatic condition in electrolyzer where

electrodes spaces separated MK-40 cation membrane. Sulfur composite electrode made

by proposed our own special ways. The effects of different parameters (current density,

electrolyte concentration and duration of electrolysis) for anodic oxidation the sulfur

that contented in the composition electrode in sodium carbonate solution is considered.

As an anode was used electric conducted sulfur electrode and as a cathode was used

graphite rod [114].

During electrolysis at the oxidation of elemental sulfur anodic side takes places

following reactions:

S + 6OH- -4e → SO32− + 3H2O E0 = -0.660 V (4.8)

S + 8OH- -6e → SO42− + 4H2O E0 = -0.753 V (4.9)

2Н2О -4е → О2+4Н+ E0 = +1.228V (4.10)

56

The effect of anodic current density for faradaic efficiency of generated sulfate

ions was studied in the range of 50-250 А/m2 at room temperature in 53.0 g/l sodium

carbonate solution.

If we pay attention, as seen in figure 4.4 sulfate ions highest current yield was

registered when lower current density on the anode. By the increasing of current

density, the current output of formatted sulfate ions decreased. Current efficiency was

135 % when current density on the composite electrode was 50 А/m2, and the current

density is 250 А/m2 which is current efficiency equal to 35.5 %. At higher current

density obtained lower current output explained by the increase in the share of

oxidation of hydroxide ions.

In the process of electrolysis the effect of the concentration of sodium carbonate

for the formation of sulphate ions the current yield was seen in figure 4.5. Electrolysis

carried out in the range of 26.5-212.0 g/l concentration of sodium carbonate solution.

С(Na2CO3) = 53.0 g/l; t = 1,0 hour; T = 25 ºС

Figure 4.4 – The influence of current density in anodic polarized sulfur-graphite

composite electrode for the formation of sulfate ions current efficiency

57

I = 50A/m2; t = 1 hour; T = 25ºС

Figure 4.2 – The influence of Na2CO3 concentrations for the formation of sulfate

ions current output by anodic polarized composite sulfur-graphite electrode

J= 50 А/m2; С (Na2CO3) = 53.0 g/l; T = 25 ºС

Figure 4.6 – The influence of electrolysis duration in anodic polarized sulfur-

graphite composite electrode to formation of sulfate ions current efficiency

58

By the increasing of the electrolyte concentration, there is a reduction in the

formation of sulfate ions current yield gradually, which consist of 142.2% when its

concentration 26.5 g/l, if increase the concentration to 212 g/l the current efficiency is

reduced by up to 121.5%.

The influence of electrolysis duration for anodic polarized sulfur-graphite

composite electrode’s oxidation in sodium carbonate solution was shown in figure.4.6.

Electrolysis was accomplished interval of 0.25-2.0 hour.

Anodic dissolved sulfur’s current output reduced by the increasing of the

electrolysis time, initial time of process oxidized elemental sulfur’s current efficiency

with formation of sulfate ions was 144.1%, if electrolysis time extended by two hours,

its value will be reduced to 46.7%.

Conclusion of section 4

In conclusion, in NaCl solution were determined that the anodic polarization

sulfur composite electrode oxidized with high current efficiency, this leads to create

simple methods to obtain inorganic compunds of elemental sulfur.

Current output of sulfate ions formed in sodium carbonate solution higher than

100% duo to the chemical reaction carried along with electrochemical process.

To compare anodic oxidation of sulfur in these two medium, in sodium chloride

obtained slfate ions purity was higher than in carbonate solution because its chemical

properties smilar to alkaline solution. In the alkaline sulfurs’ small amount is dissolved

by disproportion reaction.

59

5 ELECTROCHEMICAL PROPERTIES OF ELEMENTAL SULFUR IN

ALKALINE SOLUTIONS

5.1 Cathodic electrochemical property of elemental sulfur dissolved in

sodium hydroxide solution

The presence of aggressive sulfur compounds in the ground mass of hydrocarbons

in the most fields of Western Kazakhstan create difficulties in production,

transportation, storage and processing, which makes desulfurization of petroleum and

petroleum products particularly relevant issue.

Free sulfur is formed during petroleum and sulfur-containing gases refining

process as a result of oxidation by the conventional technology. Even with the partial

realization, the stock of sulfur increases. Sulfur piles are a growing threat to the

ecological security of the region.The sulfur was produced as byproduct of efforts to

meet environmental requirements that limit the emissions of sulfur dioxide into the

atmosphere [115].

literature is known that in the chemical industry applicable range of sulfur is very

wide [116]. A byproduct of oil production-sulfur still can not find a full-fledged

consumer collected as a waste. Therefore, to create simple methods for the production

of various compounds of sulfur is very important. The reason is very little research

electrochemical properties of elemental sulfur in inorganic environment because of

sulfur isolator, insoluble in water and acid [117].

In this work for the first time in alkaline solution dissolved sulfur’s chemical and

electrochemical properties are considered, and as a resulte of electrolysis cathodic and

anodic side generated in mining process widly used flotation reagent- sodium sulfide

and in soda production used raw material -sodium sulfate’s obtainment studied

comprehensively.

In order to study chemical behavior of elemental sulfur in alkaline solution,

grinded 50 g/l sulfur powder dissoloved in sodium hydroxide solution in the range of

20-200 g/l at the temperature of 90 ºС with mechanical mixer.

According to the literary dates [118] were shown that element sulfur reacted with

hydroxide-ions based in different mechanisms and disproportionated by following

reaction:

nS +6OH- → S𝑛2− +SO3

2− +3H2O (5.1)

2S +6OH- → S2- +SO32−+3H2O (5.2)

3S+6OH- → S2- +S2O32−+3H2O (5.3)

Therefore, when sulfur powder react with sodium hydroxide solution which could

dissoloved with the formation of sulfide, polysulfide, thiosulfate and sulfite ions. In the

composition of polysulfide ions has sulfur’s ad-atoms. Its end between 2 and 6 of that

is well known from the literature. It seems such a solution can be said sulfur alkaline

suspension solution. A part of elemental sulfur dissolved 40 g/l of sodium hydroxide

solution's electrochemical properties studied comprehensively.

For the first time the effect of current density, NaON and sulfur concentrations,

the duration of electrolysis for in alkaline solution dissolved elemental sulfur’s

60

cathodic restoration with formation of sulfide ions were studied.

This research first of all, the effect of current density for the formation of sulfate

and polysulfide ions current yield studied interval of 50-250 A/m2 at room temperature.

During electrolysis on the cathode occur the reactions of hydrogen separation and

reduction of sulfur:

S𝑛2− + 2e- = S2- +S𝑛−1

2− →∙∙∙→nS2- (5.4)

2Н2О +2е → H2+2OН- (5.5)

The product size obtained on the cathode side determined by the ion selective

electrode [119]. This electrode based on determination of the amount of a specific ion

concentration, for identified each ions used an own special electrode, which in

accordance with considered selective.

Sulfur in the alkaline solution will be different valence state. In alkaline solution

dissolved sulfur when reduced on cathode or oxidazed on the anodic, the current output

will be calculated duo to the element sulfur have been involved in electrochemical

reactions.

50 g/l S+40g/lNaОН; t = 1,0 сағ; T = 25 ºС

Figure 5.1– The influence of current density on the electrode in cathodic

polarized sulfur powder dissolved alkaline solution formed sulfide ions current

efficiency

On the cathode side is formed sulfide ions as a result of electrolysis. Generation

of sulfide ions current output decreased, according to the research the highest current

efficiency was shown on 100 A/m2. The reason that the current output of sulfide ions

higher than 100% explained by active separation of hydrogen gas with the formation

of sulfide ions.

The effect of the sodium hydroxide concentration for sulfide ions current yield as

a result of electrolysis formed is shown in figure 5.2.

The influence of alkaline concentration identified that in sulfur alkaline

61

suspension solution doesn’t effect seriously on the formation of sulfide ions current

output.

Using the optimal values obtained in previous research, the effect of electrolysis

duration for the generated sulfide ions current efficiency was studied in the range of 1-

5 hour. The result was shown in figure 5.3.

50 g/l S+40 g/l NaOH; J=50 A/m2;T = 25 ºС

Figure 5.2 – The influence of sodium hydroxide concentration for the cathodic

polarized sulfur powder dissolved alkaline solution formed sulfide ions current

efficiency

50 g/l S+40 g/l NaOH; J=50 A/m2;T = 25 ºС

Figure 5.3 – The influence of electrolysis duration for the cathodic polarized

sulfur powder dissolved alkaline solution formed sulfide ions current efficiency

62

According to the study, by the increasing of electrolysis duration, formed sulfide

ions current output at cathodic polarization reduced from 43% to 26%.

Latest studies investigated that the effect of sulfur concentration in the product

which formed on the cathode side (figure 5.4).

The results of the research was determined that by the increasing of the sulfur

concentration on the cathode formed sulfide ions current yield rose from 8% to 67%.

40 g/l NaOH;J= 50 А/m2; t = 1,0сағ; T = 25 ºС

Figure 5.4 – The influence of sulfur concentration for the cathodic polarized

sulfur powder dissolved alkaline solution formed sulfide ions current efficiency

5.2 In alkaline solution dissolved elemental sulfur oxidation with the

formation of sulfate ions

The essential problem is the presence of hydrogen sulfide in the fields of Zhanajol

and Tengiz as well. The lack of processing and sulfur application techniques leads to

serious environmental problem. Sulfur clusters are mostly accumulated in the process

of petroleum refining. With an annual capacity of 3 million tons of crude oil a stable

daily produces about 1,000 tons of sulfur. The inevitable consequence is the

technological impact of accumulated elemental sulfur and hydrogen sulfide on the

environment. Сurrently, In the Western Kazakhstan accumulated sulfur impacts on

climatic conditions of this area (extreme changes in temperature, wind, etc.), by the

day the sulfur pollution of such a large area which will can cause environmental

problems not only in Western Kazakhstan, but also in a global level.

Therefore, at the present time, is one of the most important issues is long-term

conservation of sulfur formed in the oil-gas industry and to consider new ways of

rational use in agriculture, medicine, veterinary [120].

63

A theoretical basis of to obtain sulfur compounds is to learn detailed knowledge

of the physical and chemical properties of sulfur [121].

In this work, for the first time the chemical and electrochemical properties of

sulfur in alkaline medium was studied and as a result of the electrolysis in the anode

space formed sodium sulfate compound’s optimal ways to obtain (used as a raw

material in the process of obtaining soda) were discussed comprehensively.

In order to study the chemical properties of elemental sulfur in sodium hydroxide

solution, the powdery sulfur preliminary dissolved in alkaline solution.

Literary sources [122, 123] has an information about the interaction of elemental

sulfur powder with sodium hydroxide solution occurs by a complex mechanism. Sulfur

dissolved alkaline solution have been made IR- spectroscopic analysis.

The results of the study shows that thiosulfate ions dissolved with the formation

of SO32−ions, however only in 40 g/l of sodium hydroxide solution identified that the

sodium thiosulfate ions comparatively intense dissolved than other concentration

(figure 5.5).

The following research, sulfur dissolved 40 g/l of sodium hydroxide solution

electrochemical properties were discussed in detail. By the method of electrolysis, the

influence of various parameters for the anodic oxidation of pre-prepared solution of

sulfur suspension with the formation of sulfate ions were investigated. They are:

current density, NaON and sulfur concentrations, duration of electrolysis. The optimal

condition of formed sulfate ions were discussed.

Figure 5.5 – IR spectroscopic analysis of consisting of 50 g dissolved sulfur

(volume of one liter) in 40 g/l of sodium hydroxide solution

64

In the electrolysis as the cathode 54 cm2 stainless steel and as anode 57 cm2

graphite electrodes were used.

The main influencing to the direction and speed for the accompanied reactions on

the electrode is current density. So first, the effect of current density on the electrode

for the formation of sulfate ions current output was studied in the range of 50-250 A/m2

at room temperature (figure 5.6).

Sulfur powder dissolved in the sodium hydroxide solution according to the last

section, prepared electrolyte poured into the anode and cathode side of electrolyzer.

During the electrolysis on the anode side may occurs following reactions:

SO32−+ 2OH- -2e → SO4

2− + H2O (5.5)

S𝑛2− -2e → nSº (5.6)

S+ 8OH- -6e → SO42− + 4H2O (5.7)

S2O32−+ 6ОН- -4е = SO3

2−+ H2O (5.8)

4ОН- -4е → О2+2H2O (5.9)

40 g/l NaOH + 50 g/l S;J=50 A/m2; t = 1.0 сағ; T = 25 ºС

Figure 5.6 – The influence of current density on the electrode inanodic polarized

sulfur powder dissolved alkaline solution formed sulfate ions current efficiency

Anode space of electrolyzer the formation of sulfate ions current output decreased

by the increasing of current density. This depends on additional process discharge

hydroxyl ions with the separation of oxygen. When anodic current density was 50

A/m2, the formation of sulfate ions the current yield does not exceed of 82.5 %, and at

250 A/m2 which less than 30%.

The increase in current density, active distribution of oxygen gas in the anode

leads to a reduction in the formation of sulfate ions current yield.

65

As a result of the electrolysis, the effect of the concentration of sodium hydroxide

for the formed sulfate ion current yield was shown in figure. 5.7.

As shown in the figure, we have discussed the effect of the alkaline concentration

for the formation of sulfate ions current yield, generated sulfate ions current output

minimum value was 22.5% at 20 g/l, at the 40 g/l NaOH solution gives highest current

efficiency which equal to 82.5%.

Previously received optimal result for the anodic oxidation of elemental sulfur,

the effect of electrolysis duration for the obtained sulfate ions current efficiency was

studied in the range of 1-5 hour. The result was shown in figure 5.8.

As a result of the study given that by the increasing electrolysis every time, sulfate

ions formation of current yield reduced from 81% to 12%.

50 g/l S; J=50 A/m2; t = 1.0 сағ; T = 25 ºС

Figure 5.7 – The influence of sodium hydroxide concentration for the anodic

polarized sulfur powder dissolved alkaline solution formed sulfate ions current

efficiency

As a result of the study given that by the increasing electrolysis every time, sulfate

ions formation of current yield reduced from 81% to 12%.

In the latest research, the effect of sulfur concentration for anodic side formed

product was investigated (figure 5.9).

66

50 g/l S+40 g/l NaOH; J = 50 A/m2; T = 25 ºС

Figure 5.8 – The influence of electrolysis duration for the anodic polarized

sulfur powder dissolved alkaline solution formed sulfate ions current efficiency

40 g/l NaOH; J= 50 А/m2; t = 1,0сағ; T = 25 ºС

Figure 5.9 – The influence of sulfur concentration for the anodic polarized sulfur

powder dissolved alkaline solution formed sulfate ions current efficiency

67

According to the result identified that by the increasing sulfur concentration,

anodic side formed sulfate ions current efficiency decreased gradually. This

phenomenon explained by the growth in sulfur amount leads to increase the proportion

of polysulfide ions. Oxidation of sulfur to sulfate ions used 6 electrons but oxidation

to sulfide ions needed 8 electrons.

5.3 Investigation of electrochemical properties of elemental sulfur

preliminary dissolved in alkaline solution by recording the anodic and cathodic

potentiodynamic polarization curves

A comprehensive analysis of the polarization curves forms and investigation of

its dependence on the concentration, temperature and other physical and chemical

parameters, allows you to get detailed information about the processes kinetics and

nature which carried out on the surface of the electrode.

In order to study, electrochemical properties of elemental sulfur in sodium

hydroxide solution, in the range of 10-50 g/l sulfur powder under vent cupboard at 90

S temperature while stirring with the help of a mechanical mixer dissolved in 40 g/l

aqueous solution of sodium hydroxide.

For the purpose of deep understanding the redox properties of the elemental sulfur

dissolved in alkaline solution were taken "anode" and "anode-cathode" polarization

curves with solution where different sulfur concentration of has been dissolved in 40

g/l solution of sodium hydroxide.

Preliminary sodium hydroxide dissolved sulfur electrolyte captured the anodic

potentiodynamic curves results was shown in figure 5.10.

V=50mV/s; t=25 oС; 1) С= 40g/l NaOH 2) С= 40g/l NaOH + 10 g/l S; 3) 40g/l

NaOH + 20 g/l S; 4) С= 40g/l NaOH + 30 g/l S; 5) С= 40g/l NaOH + 50 g/l S

Figure 5.10 – The anode potentiodynamic polarization curve of elemental sulfur

dissolved alkaline solution on rhodium electrode (a-polysulfide-ions oxidation

maximum (Imax) dependence on the concentration of sulfur)

68

On the anodic polarization curve of testing solution (1M sodium hydroxide) on

rhodium electrode where registered only oxidation of hydroxide-ions with formation

of oxygen (figure 5.10, curve1).

4OH- -4e → O2 +2H2O (5.10)

And this alkaline solution by the increasing of sulfur concentration in the interval

of 0-50 g/l and its its potential forced positive in the direction, on the anode

polyarogram "minus" 0.6V- "plus" 0.2V were registered two or three oxidation waves

and maximum (figure 5.10, curves 2-5). This phenomenon can be explained that

oxidation of polysulfide-ions to sulfur was a stage process.

S𝑛2−– 2e → nSo (5.11)

In alkaline solution by the increasing of sulfur concentration, the intensity

distribution of oxygen increased too. It will be decreased the intensity of oxidation of

polysulfide-ions and its shown on that maximum value of potential shifted to cathodic

side. If potential value of rhodium electrode further shifte to "plus" 1.0V side, on the

polarograma registered oxidation wave of sulfur to sulfite ions.

Alkaline solution in advance dissolved elemental sulfur’s electrochemical

properties was studied by taking anode-cathode cyclic poteniodinamic polarization

curves (figure 5.11).

V=50mV/s, T=25 oС；С; 1) 40g/l NaOH; 2) 40g/l NaOH + 10 g/l S

Figure 5.11 – The anode-cathodic cyclic potentiodynamic polarization curves of

elemental sulfur dissolved alkaline solution on rhodium electrode

69

Anodic-cathodic cyclic polarization when potential value of rhodium electrode

shifted on anodic side in the range of «minus» 0.6 and «plus» 0.2 V, as shown figure

5.10 there were registered stage oxidation peak of polysulfide-ions to elemental sulfur.

Oxidation waves of active sulfur to sulfite-ions among «plus» 0.75V– «plus» 1.0V

potential was registered on polyogramma (equation 5.12).

S + 6OH- - 4e ↔ SO32− + 3H2O (5.12)

When shifted potential of rodium electrode to cathodic side, at «minus» 0.25 V

formed sulfite ions re-reduction current wasn’t resgistered, which indicates a small

amount the sulfite and sulfate ions were formed and this irreversible reaction.

if shift rhodium electrode potential to more negative value, there is a possibility

of its restoration with the formation of polysulfide ions according to equation 5.11 due

to the reduction of sulfur to plysulfide is carried out with high speed, on the rhodium

electrode was not shown the separation of hydrogen gas.

The results of polarization curves, oxidation of sulfite ions to elemental sulfur

occurs until oxygen separation potential, in this work on the rhodium electrode,

potential observed in the territory of "plus" 1.13V. Oxygen separation of intensity

increased by formed sulfur atoms on the surface of electrode.

Anodic side of anodic-cathodic cyclic polarization, until oxygen formation

potential wasn’t registered oxidation of sulfate-ions. But the results of the special case

of Galvano static electrolysis was identified that sulfite-ions in the electrolyte during

the electrolysis was oxidized to sulfate-ions with active oxygen which formed on the

anodic side.

SO32−+2OH- -2е→SO4

2−+Н2О Ео = 0.05V (5.13)

SO32− + O2 + H2O → SO4

2− + OH- (5.14)

The potential value shifted towards cathode side from "minus" 0.5V potentials

polysulfide-ions in the solution reducted to monosulfide-ions(figure 5.11, 2-curve).

𝑆62−+2e →S2- + 𝑆5

2−+2е → ···→6 (5.13)

But polysulfide ions ions to monosulfide ions stage reduction on the

polyarogramma wasn’t registered.

On the cathode potential as above, for the first time there is no separation of

hydrogen gas, consequently, the current is losing by the formation of monosulfide-ions

according to equation 5.13. Only after a certain period of time is divided into hydrogen

gas.

By the increasing of scans rate, on the rhodium electrode a growth anodic

oxidation current maximum of polysulfide-ions to the elemental sulfur was observed

on the polarograma (figure 5.12), which that oxidation of polysulfide ions occurs in

diffusion regime.

By the increasing of scan rate, current maximum is grown too, such the connection

70

between the scan rate and the limited current size’s proportional growth identified that

oxidation of polysulfide ions carried out with diffusion mode.

40g/l NaOH + 10g/l S; T=25 oС; mV/s: 1) 25; 2)50; 3)100; 4) 150; 5) 200

Figure 5.12 – The influence of scan rate on the anodic potentiodynamic

polarization curves of elemental sulfur dissolved alkaline solution on rhodium

electrode (a- oxidation maximum (Imax) of sulfur dependence on (mV/s) the scan rate)

The effect of temperature for the anodic potentiodynamic polarization curve of in

alkaline solution dissolved elemental sulfur on rhodium electrode were investigated in

the range of 25-65 oС (figure 5.13).

With increasing of electrolyte temperature, the peak of anodic maximum current

on the voltage curve exceed too, maximum potential value was shifted towards anodic

side.

From the effects of temperature dependences, the effective activation energy of

the anodic oxidation process for elemental sulfur dissolved in alkaline solution on

rhodium electrode with dependence of lgIip - 1/T was calculated by Gorbachev [124]

method (figure 5.14), its value equal to 13.67 kJ/mol, which indicated the oxidation

reaction of sulfur occurred in diffusion mode.

71

40g/l NaOH + 10g/l S; t, 0С: 1) 25; 2) 35; 3) 55; 4)65

Figure 5.13 –The effect of temperature for the anodic potentiodynamic

polarization curves of elemental sulfur dissolved alkaline solution on rhodium

electrode (oxidation maximum (Imax) of sulfur dependence on the temperature (oС) of

electrolyte)

Figure 5.14 – In alkaline solution dissolved elemental sulfur’s lgI value

dependence on temperature (1/Т∙103)

72

5.4 Obtainment of monosulfide and investigate its electrochemical properties

by unloading polarization curves

According tothe range of anthropogenous influence to the environment and from

here arised danger level, decontamination of environmentally harmful substances, the

development of various technological processes and considering its new ways one of

the essential issues of the day. Development of new technologies to obtain eco-friendly

and wasteless product, electrochemical methods have been taken an important place.

In our country during the desulphurization stage of oil, large amounts of contained

toxic byproduct elemental sulfur will produced. The accumulation of large amounts of

sulfur emissions have caused serious environmental problems. Therefore, harmful

sulfur emission change into the commodity products that improved the economic

performance of the industry, and lead to create opportunities for the solution of

environmental problems [125,126].

At present obtaining of sulfur compounds with known methods are complicated,

expensive and is not in accordance with the requirements of the environmental

aspects.Therefore, to find a simple, inexpensive and efficient methods for synthesis

of the inorganic compounds of sulfur are today’s the main issues.

Based on this research can be made the method of obtaining the alkali metal

sulfide compounds from sulfur emissions. The principal technological schemes from

oil production generated sulfur emissions processing is shown in figure 5.16, 5.18.

X-ray phase analysis for the nature of sodium sulfide obtained by electrochemical

way was carried out with the help of the American ASTM card-indexes (figure 6.17).

The parameters of of the diffraction line intervals of sodium sulfide on the

rentgenogramma corresponds to the values of American card files (3.21 А0; 2.80 А0;

2.98 А0; 2.62 А0; 1.89А0). As well as was determined that the diffraction maximums

accordance with the crystal lattice structure of Na2S • 9H2O.

In this scientific work, preliminary dissolved sulfur powder in alkaline solution

electrolyte, for the first time, under electrolyze on the cathodic side obtained flotation

reagents-monosulfide which have been widely used in mining and its electrochemical

property studied by the method of removing the potentiodynamic polarization curves.

In order to study electrochemical property of elemental sulfur, measured between

1-10 g of sulfur powder dissolved in 40 g/l aqueous solution of sodium hydroxide at

90 0C temperature and mixed with a mechanical agitator. When sulfur completely

dissolved in the sodium hydroxide the сolour of solution will be changed orange, then

stopped hearting process and sent to cooling in water bath.

Various sulfur ions obtained the solution poured into the cathode side of

electrolytic cell with capacity of 200 ml where the space of electrode was allocated

with MK-40 cationite membrane. As an anodic and cathodic electrode were used 57

cm2 graphite and 54 cm2 titanium electrode. Electrolysis was carried out 3-4 hours,

during the electrolysis polysulfide’s ions orange-yellow color in the electrolyte to be

held gradually to colorless state. It identified that polysulfide and other ions in the

solution gradually passing to the monosulfide ions [127]:

Sn2−+ 2e → S2- + S𝑛−1

2− → ……+nS2- (5.14)

73

2SO32− + 4e + 3H2O →𝑆2O3

2−+ 6OH- (5.15)

S2O32− +8e + H2O →2S2- + 6OH- (5.16)

Completed monosulfide solution pured into special containers and is sent to the

customer or after evaporation process could be obtained sodium sulfide crystals.

1- titanium electrode, 2- cationite membrane, 3-graphite electrode

Figure 5.15 – Electrolyzer used for receive monosulfide

One of the main methods for the investigation of electrochemical reactions of

mechanisms and kinetics is considered to take a voltage curves and analysis which

was characterized the relationship between the current density with electrode potential.

Polarization curves allows to get detailed information about the nature of the reactions

occurring on electrodes [128].

Sulfur dissolved sodium hydroxide solution at the room temperature poured into

the cathode space of electrolysis, which polarized with cathodic current, and identified

that the platinum electrode "red-ox" potential value by the time changed in the form of

a wave and shiftd in the territory of negative potentials (figure 5.19). Hence, in the red-

ox system of S - 𝑆𝑛2− , polysulfide ions gradually passage to monosulfide ions, thevinert

platinum electrode potential value is moved toward the negative potential values.

74

Figure 5.16 – The principal scheme of obtainig of sodium monosulfide by

processing of sulfurwaste

75

76

1-thermostat; 2-mixer; 3 tripod; 4-current source; 5-MK-40 cation membrane; 6

- anode; 7 - cathode; 8-mass-exchange apparatus

Figure 5.18 – The fundamental technological scheme of obtainig of sodium

monosulfide by processing of sulfurwaste

77

С= (40 g/l NaOH + 7 g/l S)

Figure 5.19 – During the electrolysis (S-𝑆𝑛2−) ions red-ox potential value

dependence on the time

Measured potential value dependence on time during electrolysis shown that the

passage of polysulfide ions to monosulfide was another confirmation of cathodic

electrode process that accompanied by complex stages.

In order to deeper understanding of the oxidation properties of obtained

monosulfide ions in alkaline medium after electrolysis was studied by removing anodic

and anodic-cathodic polarization curves in alkaline different amounts of sulfur

dissolved solutions on rhodium electrode (figure 5.20).

In figure 5.20 was shown alkaline monosulfide solution’s anode-cathode cycle

potentiodynamic polarization curves on rhodium electrode after the electrolysis.

On 40 g/l NaOH solution’s anodic-cathodic potentiodynamic cyclic polarization

curve on rhodium electrode were registered only oxygen and hydrogen gases

generation current.

78

V=50mV/s; T=250С; 1)С= 40 g/l NaOH ; 2) С= 40 g/l NaOH+7 g/l S2-

Figure 5.20 – Anode-cathode potentiodynamic cyclic polarization curves of

monosulfide solution on the rhodium electrode

And the potential value of the rhodium electrode submerged in the electrolyte

have monosulfide ions shifted towards anodic side, in the potential area «plus» 0.1V -

«plus» 1.2V, on the polyarogram (figure 5.20, curve-2), newly formed sulfur’s anodic

oxidation wave to sulfite ions fixed clearly (5.17-reactions).

S + 6OH- - 4e →S𝑂32−+3H2O E0= -0.660V (5.17)

In figure 5.19 oxidation of monosulfide ions to elemental sulfur is not observed,

but at low current density captured polarization curves, specially at high temperatures,

in the potential space "minus" 0.5 V "plus" 0.2V were registered two or three waves of

oxidation (figure 5.21). This wave can be judged the monosulfide ions’s stage

oxidation related with the formation of disulfide, polysulfide further elemental sulfur.

The rhodium electrode potential shifted towards anode side, the first monosulfide-

ion is oxidized to elemental sulfur atom by taking two electrons, at the same time which

joined with other monosulfide and formed disulfide-ion, while this gradually formed

𝑆62−- ploysulfide ions, then sulfur atoms.

6𝑆2−-2e→𝑆0 +5𝑆2−→ 𝑆22−+4S0– 2e →…𝑆6

2−-2e→ 6𝑆0 (5.18)

On the polyarogram does not registered all of the stage oxidation waves of

monosulfide ions. In the potentials territory of "Plus" 1.2 V on polyarogram was

registered oxygen gas separation current. As you can see the curvature of the

79

polarizing, monosulfide ions in an alkaline solution oxygen gas is divided by high

voltage.

The potential of electrode forced from the anodic to cathodic potentials area,

reduction wave of formed products were not registered, only at "minus" 1.2 V potential

there is a current of hydrogen gas separation.

An enlarged scale of anodic potentiodynamic polarization curves of rhodium

electrode's in sulfur dissolved alkaline solution is can be seen from figure 5.21, it is

shown on the polyarogram the anodic oxidation waves of monosulfide ions to the

elements sulfur and its the number of maximums are increased gradually.

40g/l NaOH + 7 g/l S; T, 0С: 1-25; 2-35; 3-45; 4-55; 5-65;

Figure 5.21 – Anodic potentiodynamic polarization curves of rhodium electrode

in monosulfide solution from "minus" 0.5 to "plus" 0.28 V

On the polyarogram was registered that by the increasing scan rate the oxidation

peak elemental sulfur to sulfite ions increased (figure 5.23). This explained oxidation

of sulfur could take a place in diffusion regime.

The effect of temperature for the anodic potentiodynamic polarization curve of

monosulfide ions in alkaline solution on rhodium electrode were investigated in the

range of 25-65 °C (figure 5.24).

It’s visible to see an increase in the number of oxidation waves due to the increase

in temperature, on polyarogram registered in the territory of "minus" 0.4V, "plus" 0.1V

and "plus" 1.0 V. 1st peak shows oxidation of monosulfide ions up disulfide ions, next

peak up to "plus" 0.8V waves it is due to polysulfide ions to the formation of elemental

sulfur in stages. In the territory "plus" 1.2V -1.4V potentials can be explained by

oxidation of sulfite ions to sulfate ions.

80

V=50mV/s; T=250С; 1) С= 40g/l NaOH +1 g/l S2- ; 2) С= 40g/l NaOH + 5 g/l

S2-; 3) С= 40g/l NaOH + 7 g/l S2- ; 4) С= 40g/l NaOH + 10 g/l S2- ; 5) С= 40g/l NaOH

+ 20 g/l S2-

Figure 5.22 – Anodic potentiodynamic polarization curves various amount of

sulfur contained monosulfide solution on rhodium electrode

40g/l NaOH + 7 g/l S2-; T=25ºС; v, mV/s: 1-25; 2-50; 3-100; 4-150; 5- 200

Figure 5.23 – The influence of scan rate on the anodic potentiodynamic

polarization curve of monosulfide ions in alkaline solution on rhodium electrode (a-

oxidation maximum (Imax) of sulfur dependence on (mV/s) the scan rate)

81

40g/l NaOH + 10g/l S; T=250С; t, 0С: 1) 25; 2) 35; 3) 55; 4)65

Figure 5.24 – The effect of temperature for the anodic potentiodynamic

polarization curves of alkaline monosulfide solution on rhodium electrode (oxidation

maximum (Imax) of sulfur dependence on the temperature (0С) of electrolyte

Сурет 5.25 – lgI value of monosulfide ions in electrolyte dependence on

temperature (1/Т∙103)

82

From the effects of temperature dependences on the stage oxidation of alkaline

monosulfide solution ions was calculated activation energy of the process (figure 5.25),

which value equal to 13.43 kJ/mol, that shown the oxidation reaction of monosulfide

on the rhodium electrode occurred in diffusion mode.

Conclusion of section 5

Conclusion, from alkaline sulfuric suspension electrolyte made by the way of

chemical dissolution of elemental sulfur determined that as a result of the electrolysis

could be obtain sulfide ions with a high current yield. The amount of sulfide ions were

identified by the ion selective electrode.

For the first time, through the dissolution of elemental sulfur made alkaline sulfur

suspension electrolytes’ the oxidation regularities with formation of sulfate ions were

investigated by electrolysis method. The amount of sulfate ions from electrolysis was

determined by quantitative analysis method.

For the first investigation of the electrochemical properties of elemental sulfur

dissolved in alkaline solution using the method of removing the potentiodynamic

polarization curves on rhodium electrode. Formed polysulfide-ions by dissolving

sulfur in sodium hydroxide solution, at cathodic polarization reduced to monosulfide-

ions, but it shows anodic polarization until the formation of oxygen, which oxidized

elemental sulfur to sulfite-ions.

The various amount of elemental sulfur dissolved in alkaline solution as a result

of electrolysis obtained monosulfide ions electrochemical behavior for the first time

studied by method of removing anodic and anodic-cathodic the potentiodynamic

polarization curves. Anodic oxidation of monosulfide ions to sulfite and sulfate ions

could occurred with stage formation of intermediate product of disulfide, polysulfide

and elemental sulfur.

83

6 RECEIVE OF COPPER SULFIDE AND ITS ELECTROCHEMICAL

BEHAVIOR

At present, in the synthesis of the inorganic compounds of non-ferrous metals,

using of electrolysis with stable and the industrial AC frequency currents gives

effective results so that is has been used widely in many industries. Also, in the

processing of non-ferrous metals of sulfur ore a large quantities of chalcogen are

produced as waste, therefore, to obtain there useful compounds, concentrate and

protection of the environment from poisoning methods should be considered

comprehensively [129]. By electrochemical methods creation of a non-waste

technology and improvement of its measures are considered as a effective way to solve

a number of environmental issues. The carried out results of the research work show

the effective opportunities in the creation of simple methods to obtain many of metal

salts [130]. In the republic, the main source of income for the country's economy

considered – oil refining, with the increase in the production area, one of the top arising

issue is undeveloped elemental sulfur’s open accumulation. In order to increase rational

use of natural resources of elemental sulfur, professor Baeshova and his scientific staff

has been done the number of studies in the direction of "to reveive metal sulfide" [131-

135], contributed to the elimination of dependence on imported flotation reagents

which applied in the field of mining and processing. It is well known that there are a

number of advantages in inorganic compounds of metals produced by electrolysis

[136].

The main aim of the proposed work, to study the influence of various parameters

for the reduction process of copper (II) ions with sulfite ions in the aqueous solutions,

which: current density on the cathode, copper (II) and sulfite ions concentration, the

concentration of sulfur acid, electrolysis duration.

Preliminary studies identified that in acid aqueous medium the copper (II) and

sulfite ions reduced along with on cathode by the formation of copper sulfide powders.

In the process of electrolysis first of all, the effect of current density on the

titanium electrode for the formation of copper sulfide powders current yield was

investigated at intervals between150 – 300 A/m2. Electrolysis was carried out in

electrode space retained 150 ml electrolyzer. As a cathode 6 cm2 titanium and as a

anode 9.2 cm2 copper electrodes were used. For the main research, as a electrolyte was

used the mixed solution of 10 g/l of sodium sulphite, 7.5 g/l of copper (II) sulphate and

50 g /l sulfuric acid. After electrolysis, the fromed powder is filtered, and washed with

distilled water, then processed with sulfuric acid solution, against

Filtered out and rinse with distilled water, at the end dried. The obtained powder

searched by the method of X-ray and identified that black copper sulfide (CuS) powder

is formed.

During the electrolysis the copper (II) and sulfur (IV) ions can be reducted on the

cathode by following reactions:

Cu2+ + 2e → Cuo Eo= + 0.34 V (6.1)

SO32-+ 4e + 6H+ = So + 3H2O E0 = + 0.45 V (6.2)

84

The newly formed active sulfur and copper atoms can quickly interact with each

other and created copper sulfide:

Cu + S → CuS (6.3)

2Cu + S → Cu2S (6.4)

10g/l Na2SO3+ 7.5g/l CuSO4+ 50g/l H2SO4,T= 25 0C, t= 1hour

Figure 6.1 – The influence of current density for the formation of copper sulfide

powder

As seen in figure 6.1, by the increasing of current density, the formation of copper

sulfide current output decreased. This explained by the increasing of additional

hydrogen separation share with a reaction of 6.5:

2Н+ + 2е → Н2 (6.5)

In figure 6.2, the effect of the concentration of copper (II) ions for the formation

copper sulfide powders current yield was discussed.

85

10g/l Na2SO3 + 50g/l H2SO4,Jk= 200 А/m2,T= 25 0C, t= 1hour

Figure 6.2 – The influence of copper (II) ions concentration for the formation of

copper sulfide powder

As shown, with increasing of copper (II) ions, the formation of sulfide powder

current efficiency at the first rose to 100 % then higher concentration which reduced.

This is illustrated by high concentration, the copper ions formed copper (II) sulfide

along with the copper powder. At high concentrations additional elemental copper

powders formed so obtained powder dissolved in diluted sulfuric acid then inflated by

the air. After that copper sulfide filtered again and rinsed distilled water, dried, then

the weight was measured. Consequently, by the growing copper (II) ion concentration,

the formation of the pure copper powder share started increase. Again, it should be

noted that copper (II) ions concentration’s rise to create an opportunity in the

generation of Cu2S compounds.

The effect of sodium sulfite concentration for the formation of copper sulfide

powders current yield was studied (figure 6.3).

Sodium sulfite concentration’s optimal condition were observed at 10 g/l. This

phenomenon explained by high concentration of sodium sulfite during electrolysis with

copper sulfide additional substances, mainly due to the formation of elemental sulfur.

The effect of sulfuric acid concentration for the formation of the copper sulfide

powders current yield are shown in table 6.1. As seen determined that the concentration

of sulfuric acid does not affect the current yield.

86

J=200 А/m2, С =7.5g/l CuSO4 + 50g/l H2SO4, t=1hour, T= 25 оC

Figure 6.3 – The influence of sodium sulfite concentration for the formation of

copper sulfide powder

Table 6.1– the influence of sulfuric acid for the formation of copper sulfide powder

current efficiency

С(Н2SO4) 50 100 150 200

Ƞ, % 97.2 93.2 93.4 93.6

In the final research, the effect of electrolysis duration for the formation of copper

sulfide powder was studied (figure 6.4). On the basis of the achieved results identified

that by the time, for the generation of copper powder current output at the 1st hour

which reached to 93%, but after four hour of electrolysis its value reduced to 27%.

Copper (I) sulfide powders roentgenogram was shown in figure 6.6. The results

of the study showed that 1.67; 1.86; 1.94; 2.37; 2.62; 2.88; 3.00; 3.19; 3.33 reflexes -

CuxS (ASTM 23-957), (1.96> x> 1.86). In addition, when the obtained powder was

sent for elemental analysis too, which shown the powder contained 63.63% copper,

and 31.03% of the sulfur.

87

J= 200 А/m2, С= 10g/l Na2SO3+ 7.5 g/l CuSO4+50 g/l H2SO4, T= 25 оC

Figure 6.4 – The influence of electrolysis duration for the formation of copper

sulfide powder

Figure 6.5 – Copper(II) sulfide powders roentgenogram

88

Figure 6.6 – Copper(I) sulfide powders roentgenogram

Conclusion of section 6

The main parameters of copper sulfide particles output current were studied such

as. The density of current the ions of copper (II), the consent ration of sulphate sodium

sulfide, the time duration. The highest output of copper sulfite was shown in optimal

condition

The results of the research, two-valent ions of copper and four-valent sulfur ions,

when reduced along with in sulfuric acid solutiom on the titanium electrode shown the

formation of copper sulfide powder. Based on obtained indicators can be create the

receipt method of copper sulfide. The main product of the electrolysis were copper

sulfide CuS and the Cu2S powder.

Тhe obtained powder was analysed with X-rays and which determined that

powder was the copper sulphade. Аt the same time,when we sent the powder to

elemental analysis was identified that the composition of powder contained with

63.63% of copper 31.03% of sulfur.

89

7 CREATION OF CHEMICAL POWER SOURCE BY USING

OXIDATION REACTIONS ON THE SULFUR COMPOSITION ELECTRODE

7.1 The regularities of the formation of motive force in the galvanic pair of

"sulfur-graphite" - "lead dioxide"

All over the world, including in our country, one of the main directions of the

strategy for the industrial and innovative development is power supply of the

population. XXI century in the world, especially in developing countries, rapidly

growing in useing of electricity. Global consumption energy in every fifty years, the

limit of growth will be expected to increase more than twice. This growth due to the

growth of population, economic development and increase in use of electricity. Of

course, energy should be manufactured by without decreasing the environmental

situation. for a long time has been used coal, oil, natural gas and other energy sources

exhaustion or reduction of fund, in addition the harmful effects on the environment is

growing by the day.

At present, there is a shortage of energy in the world and in order to get rid of it,

there have been done a lot of work. Including the environmental problems effective

solutions is a non-waste technology that was popular modernity topics [137].

Currently, in the world more than 500 chemical power sources (CPS)

electrochemical was systems, only about 40-50 of them carried out the practical side.

All over the world annually produced number of batteries the accumulator exceeds

more than billion. One of the world's largest producers in the production of various

types of power sources and great contribution to the energy sector are: VARTA,

Hawker Batteries Group, FIAMM, Benning, Chloride Power Electronics, American

Power Conversion, Best Power, ABZ Aggregate-Bau GmbH, SDMO, Toshiba,

Siemens, Duracell and etc. [138-142].

According to the principle of work CPS divided into three groups: primary,

secondary and fuel cells. Primary electrodes CPS or galvanic cells constitute of active

substances after a full consuming power sources stops there work. Secondary CPS

(batteries) after consuming the active substances (row) again charged with an electric

current. And primary chemical power sources can be attributed a reserve elements. The

main difference will be which is unemployed condition for a long time. Its three main

reasons: electrodes can be isolated electrolyte, can be solid state, chemically inert, or

do not participate at all. Reserve battery will be ready to work only when they are faced

with the state of activation [143-145].

Today is one of the main directions to increase functional index of modern

chemical power sources, They are differ from high values of EMF and SCC, non

negative impact of electrode material on the environment and efficiency in the

economic context [146].

In this work, for first time as a negative electrode was used composite of sulfur-

graphite. In our country at the present day, from oil production more than one million

tonnes of elemental sulfur was accumulated [148].

In this regard, to obatain the chemical power sources in the use of elemental sulfur

has a special significance and could be one of the solutions in solving the

90

environmental problem.

In this proposed work as a chemical current source submerged in a solution of

sulfuric acid in the galvanic pair of "sulfur-graphite" and "lead dioxide" at between the

electrodes presented electro motive forces formation of regularities was investigated

[149]. For example:

(С)S | H2SO4 | PbO2

Phenomenon of the formation electric motive force in these galvanic pair was

studied. Research was carried out with capacity of 100 ml glass electrolyzer. This

dishes is filled with sulfuric acid, as electrode "lead dioxide" and "sulfur-graphite"

composite wereused. Sulfur and graphite electrodes - serves as the negative pole of the

galvanic cell and lead dioxide the positive pole. Experimental installation is shown in

figure 7.1.

Electrodes directly connected to the voltmeter and the electromotive force (EMF)

values to be measured constantly. And after the period of time (10 minutes) ammeter

connected to the chain, the short circuit current (SCC) identified then which put off

again. Lead dioxide electrodes prepared by placing in the middle of plastic cylinder

with small holes all the side which was filled lead sulphate through the anode

polarization under condition of current I = 0.13A, EMF E = 3.1V and t = 20 min.

Preparation of composition sulfur-graphite electrodes has been done through [147,148]

professor A.B Baeshov with his disciples proposed methods.

1-lead sulfate powder; 2-lead electrode; 3-sulfur-graphite composite electrode;

4-sulfuric acid solution; 5-аmmeter; 6-voltmeter

Figure 7.1– Installation scheme for the study of the phenomence of the

formation of electric current in "(C) S - PbO2" galvanic pair

91

During the research, the influence of sulfuric acid solution concentrations and

time for the formation regularity of electro motive force and short circuit current in the

galvanic pair of "sulfur-graphite" and "lead dioxide" at between the electrodes was

investigated.

Galvanic pairs of "(C) S - PbO2" between the electrodes, the electro motive force

(a) and short circuit current (b) valus changes by the time was shown in figure 7.2, 7.3.

According to the results of the experiment identified that EMF provides the maximum

value of 1050 mV, and initially the value of SCC is equal to 40mA further its value

will begin to decline.

The influence of sulfuric acid concentration for the formation of short circuit

current and electro motive force was studied in the range of 25-200 g/l (figure 7.4, 7.5).

When increasethe concentration of sulfuric acid from 25 - 125 g/L the values of

EMF and SCC increased dramatically, and at higher concentrations shown reduction.

By increasing of sulfuric acid concentration, a rise in the values of EMF and SCC

can be explained by the increase in the electrical conductivity of the electrolyte. A

decrease in high concentration of acid which can be illustrated by inhibition of

elemental sulfur’s (equation 7.1) oxidation reaction.

On sulfur electrode takes place following reaction, sulfur oxidized and ions will

be held to the solution [149]:

S + 3H2O – 4e → H2SO3 + 4Н+ Е0 = 0.450 V (7.1)

The electrons by the external chain from sulfur - graphite electrode through the

lead dioxide (PbO2) where the basis of the reduction reaction lead sulfate is formed:

PbO2+SO42−+ 4Н++2е = PbSO4+ 2Н2О Е0 = 1.682 V (7.2)

In terms of the theory the value of EMF generated between the two electrodes

must be as follows:

Е = Е1 – Е2 = 1,682 –0,450 = 1.232 V

As well, in this we proposed galvanic element, oxidation reaction of composition

sulfur graphite electrode (equation 7.1) and reduction reaction of lead dioxide is carried

out by (equation 7.2). Consequently, sulfur galvanic cell plays the role of negative

charged electrode and PbO2–is positively charged

92

Figure7.2 – The quantity of EMF formed between the electrodes in "(C) S -

PbO2" galvanic pair changes by the time: (100 g/l H2SO4)

Figure 7.3 – The amount of SCC formed between the electrodes in "(C) S -

PbO2" galvanic pair changes by the time: (100 g/l H2SO4)

93

Figure7.4 – The quantity of EMF formed between the electrodes in "(C) S -

PbO2" galvanic pair depence on the concentration: (t=10 min)

Figure7.5 – The quantity of SCC formed between the electrodes in "(C) S -

PbO2" galvanic pair depence on the concentration: (t=10 min)

94

Conclusion of section 7

In the sulfuric acid solution "sulfur and lead dioxide" galvanic pair can be used as

a chemical power source in laboratories. This shown galvanic pair, for the first time

element sulfur can be used to obtain electric current.

Galvanic pairs of "(C) S - PbO2" between the electrodes, the electro motive force

and short circuit current valus changes by the time and concentration of electrolyte

were investigated. Maximum values of SCC and EMF concentrations sulfuric acid in

the range of 50-125 g/l registered. The value EMF is 1050mV and SCC value equal to

40 mA.

95

CONCLUSION

In this dissertational work, for the first time by DC polarized sulfur-graphite

electrodes’ electrochemical anodic dissolution in aqueous solutions of hydrochloric

acid and neutral (Na2CO3, NaCl) and preliminary sodium hydroxide dissolved sulfur’s

redox regularities were studied. For electrochemical process the effects of current

density on the electrode, solution concentration and the duration of the electrolysis

were discussed. Based on the concluded literature review and carried experiment

results, the possibilities of synthesis of inorganic compounds of sulfur by

electrochemical way was shown.

According to the results of conducted comprehensive study the following

conclusions have been drawn:

- electrochemical properties of elemental sulfur preliminary dissolved in alkaline

solution studied on rhodium electrode by unloading anodic and anodic-cathodic

potentiodynamic polarization curves. According to the polyogramms, on the anode

oxidation of polysulfide ions carried out with stage process. By temperature- kinetic

method the effective activation energy of the anodic oxidation process of polysulfide

ions was identified, which is equal to 13.67 kJ/mol, this illustrated oxidation of

polysulfide ions took away with restriction of diffusion.

- elemental sulfur preliminary dissolved in alkaline solution formed ions which

electrochemical behaviors for the first time was investigated. Under optimal condition

sulfate ions current yield on the anode was 81%, and at the cathode polarization formed

sulfide ions current yield was equal to 46.7%.

- in alkaline solution in advance sulfur dissolved and the generated ions by

cathodic polarization was obtained monosulfide solution, and for the first time its

electrochemical properties comprehensively studied by unloading anodic and

cyclicpotentiodynamic polarization curves. Activation energy of oxidation process,

with dependence of lgIip - 1/T was calculated by Gorbachev’s method its value equal

to 13.43 kJ/mol.

-in alkaline medium the polysulfide consist solution polarized on cathodic side

and its "red-ox" potential value measured on inert platinum electrode. Over time, for

the first time identified that the red-ox potential varied six forms of wave. These

research results identified in polysulfide ions 𝑆𝑛2−- the value of “n” equal to six.

Determined that, by the time on the cathode side yellow coloured polysulfide ions, due

to the formation of monosulfide ions its changed colorless solution.

- anodic properties of sulfur-containing composite electrode were studied.

Shown that the sulfur oxidized with formation of sulfate ions. For the first time at

optimal condition sulfur in hydrochloric acid solution current output by the formation

of sulfate ions achieve up to 52%.

- two-valence ions of copper and four-valence sulfur ions, when reduced along

with in sulfuric acid solution on the titanium electrode identified the formation of

copper sulfide powder. Optimal conditions the formation of copper sulfide powders

were determined;concentration of electrolyte 10g/l Na2SO3+ 7.5 g/l CuSO4+50 g/l

H2SO4, current density 200 А/m2, electrolysis duration 1 hour.

96

-sulfur contain composition electrodes’ anodic oxidation in Na2CO3 and NaCI

solution were studied comprehensively. At anodic side formed sulfate ions current

output were 135% and 94%.

-for the first time shown that chemical current source can be made by using the

oxidation reaction of composite conductive sulfur-sulfur graphite electrode. Novelty

of introduced method was protected by innovation patent of RK (№ 31177). This

specified galvanic pair was determined that the value EMF is 1050mV and SCC value

equal to 40 mA. The galvanic pair of "sulfur and lead dioxide" in the sulfuric acid

solution can be used as a chemical power source in laboratories.

97

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