kltn newest Thủy.pdf

VIETNAM NATIONAL UNIVERSITY, HA NOI

VNU UNIVERSITY OF SCIENCE

FACULTY OF CHEMISTRY

Phm Nh Thy

OXIDATIVE DENATURATION OF ACTIVATED CARBON SURFACE

BY KMnO4 FOR IONS TREATMENT IN WATRER ENVIRONMENT

Hanoi, June 2015

Oxidative denaturation of activated carbons surface by KMnO4 for ion treatment in water environment

1

ACKNOWLEDGEMENTS

I would like to express my special thanks of gratitude to my

Supervisor Prof.Dr.Sci.Tran Hong Con for giving me the topic and his keen

guidance in preparing this report as well as our principals who gave me the

golden opportunity to do this wonderful project on the topic Research the

changing surface properties of activated carbon oxidized by KMnO4, which

also helped me in doing a lot of Research and I came to know about so many

new things.I am really thankful to them.

Secondly I would also like to thank my parents and friends who

helped me a lot in finishing this project within the limited time.

I am making this project not only for marks but to also increase my

knowledge.

Ha noi, April 8, 2014

Pham Nhu Thuy


2

CONTENTS

ACKNOWLEDGEMENTS ...................................................................................... 1

CONTENTS ............................................................................................................... 2

LIST OF FIGURES .................................................................................................. 4

LIST OF TABLES .................................................................................................... 5

INTRODUCTION ..................................................................................................... 6

Chapter 1. Overview ............................................................................................. 7

1.1. Activated Carbon ........................................................................................... 7

1.2. Porous Structure of Activated Carbon Surface ............................................ 9

1.3. Chemical Structure of Activated Carbon Surface ...................................... 12

1.3.1. Carbon-Oxygen Surface Groups ........................................................... 13

1.3.2. Characterization of Carbon-Oxygen Surface Groups ........................... 14

1.4. Applications of Activated Carbons ............................................................ 16

Chapter 2. Experiments and methods .............................................................. 18

2.1. Research objective ....................................................................................... 18

2.2. Equipment and chemical ............................................................................. 18

2.2.1. Equipments ........................................................................................... 18

2.2.2. Chemical subtance ................................................................................ 19

2.3. Material ........................................................................................................ 19

2.4. Method of examining features of denatured activated carbon .................... 21

2.4.1. Determination of KMnO4 consumption and total electrons exchanged

21

2.4.2. Determination of acid groups in activated carbon and oxidized

activated carbon .................................................................................................. 21

2.5. Method for determination of ions in solution .............................................. 22


3

2.5.1. Determination of ammonium concentration ......................................... 22

2.5.2. Determination of Arsenic concentration ............................................... 24

2.6. Method of calculating the adsorption capacity of the material ................... 26

2.6.1. Investigation of ion adsorption capacity ............................................... 26

2.6.2. Investigation of adsorption equilibrium time ....................................... 28

2.6.3. Determination of the maximal adsorption ............................................ 29

Chapter 3. Results and Discussion .................................................................... 30

3.1. Determination of KMnO4 consumption of activated carbon ....................... 30

3.2. Preliminary determination of total acid center on activated carbons surface30

3.3. Investigation of Arsenic adsorption capacity of the material ...................... 33

3.3.1. Investigation of Arsenic adsorption equilibrium time .......................... 33

3.3.2. Determination of the maximal arsenic adsorption capacity ................. 34

3.3.2.1. Material AC-1 ................................................................................ 34

3.3.2.2. Material AC-2 ................................................................................ 35

3.3.2.3. Material AC-2(B) ........................................................................... 36

3.3.2.4. Material AC-2(A) ........................................................................... 37

3.4. Investigation of ammonium adsorption capacity of the material ................ 38

3.4.1. Investigation of ammonium adsorption equilibrium time .................... 38

3.4.2. Determination of maximal ammonium adsorption of material AC2(B)

39

3.4.2.1. Material AC-2(B) ........................................................................... 40

3.4.2.2. Material AC-2(A) ........................................................................... 41

CONCLUSION ........................................................................................................ 43

REFERENCES ........................................................................................................ 44


4

LIST OF FIGURES

Figure 1.1: the macropores (a), the mesopores (b) , and the micropores (c)[5]. ...... 11

Figure 1.2: The reactions of activated carbons with oxygen gas .............................. 14

Figure 1.3: Functional groups of basic character: (a) chromene, (b) pyrone-like. ... 16

Figure 1.4: Model of a fragment of an oxidized activated carbon surface. .............. 16

Figure 2.1: Calibration curve of ammonium ............................................................. 23

Figure 2.2: Calibration curve of As .......................................................................... 26

Figure 3.1: Titration curve of AC and denatured AC ............................................... 32

Figure 3.2: The Arsenic adsorption equilibrium time ............................................... 33

Figure 3.3: The Langmuir adsorption isotherm of AC-1 .......................................... 34

Figure 3.4: The Langmuir adsorption isotherm of AC-2 .......................................... 35

Figure 3.5: The Langmuir adsorption isotherm of AC-2(B) ..................................... 37

Figure 3.6: The Langmuir adsorption isotherm of AC-2(A) .................................... 38

Figure 3.7: The Ammonium adsorption equilibrium time ........................................ 39

Figure 3.8: The Langmuir adsorption isotherm of AC-2(B) ..................................... 40

Figure 3.9: The Langmuir isotherm of AC-2(A) ...................................................... 41


5

LIST OF TABLES

Table 2.1: Chemical substances ................................................................................ 19

Table 2.2: The standard curve of NH4+ ..................................................................... 23

Table 2.3: The standard curve of arsenic .................................................................. 26

Table 3.1: Consumption of KMnO4 for oxidation of activated carbon .................... 30

Table 3.2: pH of original and oxidized activated carbon with corresponding volume

of NaOH 0.01M ........................................................................................................ 31

Table 3.3: The data of arsenic adsorption equilibrium time of material AC2(B) ..... 33

Table 3.4: The examination data of material AC-1 .................................................. 34

Table 3.5: The examination data of material AC-2 .................................................. 35

Table 3.6: The examination data of material AC-2(B) ............................................. 36

Table 3.7: The examination data of material AC-2(A) ............................................. 37

Table 3.8: The data of ammonium adsorption equilibrium time of material AC-2(B)

................................................................................................................................... 39

Table 3.9: Langmuir examining results of material AC-2(B) ................................... 40

Table 3.10: Langmuir examining results of material AC-2(A) ................................ 41


6

INTRODUCTION

Exacting demands are being made upon existing water resources to meet the

requirements of a highly industrialized society. These demands can be expected to

mount in the future, for continuing population expansion and tech non-logical

development lead naturally to both more extensive and more intensive use of

available supplies of water, and ultimately to the pollution and degradation of the

quality of these waters. Much of the water currently available to a large segment of

society has been subjected to previous use. Indeed, multiple reuse of water is not

uncommon today; planned and deliberate reuse is expected to be an even more

significant factor in water resources management in the years ahead. Evidently, as

reuse practice increases, more stringent requirements will be placed on the

treatment of waters and wastewaters, and more effective removal of persistent

materials, which might otherwise build up to intolerable concentrations during

several reuse cycles, will be required.

To increase the efficiency of water treatment, there are many methods

including methods of surface modification of activated carbon with HNO3, halogen,

sulfured, N2,... In this research, I focus on oxidative denaturation of activated

carbon surface by KMnO4 for ions treatment in water environment.


7

Chapter 1. Overview

1.1. Activated Carbon[3]

Activated carbon, also called activated charcoal, activated coal, carbon

activates or an AC filter, is a form of carbon processed to have small, low-

volume pores that increase the surface area available for adsorption or chemical

reaction.[6]

Activated carbons in the form of carbonized wood charcoal have been used

for many centuries. The Egyptians used this charcoal about 1500 BC as an

adsorbent for medicinal purposes and also as a purifying agent. The ancient Hindus

in India purified their drinking water by filtration through charcoal. The first

industrial production of activated carbon started about 1900 for use in sugar refining

industries. This activated carbon was prepared by the carbonization of a mixture of

materials of vegetable origin in the presence of metal chlorides or by activation of

the charred material by CO2 or steam. Better quality gas-adsorbent carbons received

attention during World War I, when they were used in gas masks for protection

against hazardous gases and vapors.

Activated carbons are unique and versatile adsorbents, and they are used

extensively for the removal of undesirable odor, color, taste, and other organic and

inorganic impurities from domestic and industrial waste water, solvent recovery, air

purification in inhabited places, restaurants, food processing, and chemical

industries; in the removal of color from various syrups and pharmaceutical

products; in air pollution control from industrial and automobile exhausts; in the

purification of many chemical, pharmaceutical, and food products; and in a variety

of gas-phase applications. They are being increasingly used in the field of

hydrometallurgy for the recovery of gold, silver, and other metals, and as catalysts

and catalyst supports. They are also well known for their applications in medicine

for the removal of toxins and bacterial infections in certain ailments. Nearly 80%

(~300,000 tons/year) of the total activated carbon is consumed for liquid-phase


8

applications, and the gas-phase applications consume about 20% of the total

production.

Because the activated carbon application for the treatment of waste water is

picking up, the production of activated carbons is always increasing. The

consumption of activated carbon is the highest in the U.S. and Japan, which

together consume two to four times more activated carbons than European and other

Asian countries. The per capita consumption of activated carbons per year is 0.5 kg

in Japan, 0.4 kg in the U.S., 0.2 kg in Europe, and 0.03 kg in the rest of the world.

This is due to the fact that Asian countries by and large have not started using

activated carbons for water and air pollution control purposes in large quantities.

Carbon is the major constituent of activated carbons and is present to the

extent of 85 to 95%. In addition, activated carbons contain other elements such as

hydrogen, nitrogen, sulfur, and oxygen. These heteroatoms are derived from the

source raw material or become associated with the carbon during activation and

other preparation procedures. The elemental composition of a typical activated

carbon is found to be 88% C, 0.5% H, 0.5% N, 1% S, and 6 to 7% O, with the

balance representing inorganic ash constituents. The oxygen content of the activated

carbon, however, may vary between 1 and 20%, depending upon the source raw

material and the history of preparation, which includes activation and subsequent

treatments. The most widely used activated carbon adsorbents have a specific

surface area on the order of 800 to 1500 m2/g and a pore volume on the order of

0.20 to 0.60 cm3g

-1. The pore volume, however, has been found to be as large as 1

cm3/g in many cases. The surface area in activated carbons is predominantly

contained in micro-pores that have effective diameters smaller than 2 nm.

Activated carbons are mainly and almost exclusively prepared by the

pyrolysis of carbonaceous raw material at temperatures lower than 1000C. The

preparation involves two main steps: carbonization of the raw material at

temperatures below 800C in an inert atmosphere, and activation of the carbonized

product between 950 and 1000C. Thus, all carbonaceous materials can be


9

converted into activated carbons, although the properties of the final product will be

different, depending upon the nature of the raw material used, the nature of the

activating agent, and the conditions of the activation process. During carbonization

most of the non-carbon elements such as oxygen, hydrogen, nitrogen, and sulfur are

eliminated as volatile gaseous products by the pyrolytic decomposition of the

source raw material. The residual elementary carbon atoms group themselves into

stacks of aromatic sheets cross-linked in a random manner. The mutual arrangement

of these aromatic sheets is irregular and, therefore, leaves free interstices between

the sheets, which may become filled with the tarry matter or the products of

decomposition or at least blocked partially by disorganized carbon. These

interstices give rise to pores that make activated carbons excellent adsorbents. The

char produced after carbonization does not have a high adsorption capacity because

of its less developed pore structure. This pore structure is further enhanced during

the activation process when the spaces between the aromatic sheets are cleared of

various carbonaceous compounds and disorganized carbon. The activation process

converts the carbonized char into a form that contains the largest possible number

of randomly distributed pores of various shapes and sizes, giving rise to a product

with an extended and extremely high surface area.

1.2. Porous Structure of Activated Carbon Surface [3]

Activated carbons with a random arrangement of micro-crystallites and with

a strongcross-linking between them have a well-developed porous structure. They

have relatively low density (less than 2 gm/cm3) and a low degree of graphitization.

This porous structure formed during the carbonization process is developed further

during the activation process, when the spaces between the elementary crystallites

are cleared of tar and other carbonaceous material. The activation process enhances

the volume and enlarges the diameters of the pores. The structure of the pores and

their pore size distribution are largely determined by the nature of the raw material

and the history of its carbonization. The activation also removes disorganized

carbon, exposing the crystallites to the action of the activating agent and leads to the


10

development of a micro-porous structure. In the latter phase of the reaction, the

widening of existing pores and the formation of large pores by burnout of the walls

between the adjacent pores also takes place. This causes an increase in the

transitional porosity and macro-porosity, resulting in a decrease in the micro-pore

volume. According to Dubinin and Zaverina, a micro-porous activated carbon is

produced when the degree of burn-off is less than 50% and a macro-porous

activated carbon when the extent of burn-off is greater than 75%. When the degree

of burn-off is between 50 and 75%, the product has a mixed porous structure and

contains all types of pores.

Activated carbons are associated with pores starting from less than a

nanometer to several thousand nanometers. Dubinin proposed a classification of the

pores that has now been adopted by the International Union of Pure and Applied

Chemistry (IUPAC). This classification is based on their width (w), which

represents the distance between the walls of a slit-shaped pore or the radius of a

cylindrical pore. The pores are divided into three groups: the micropores, the

mesopores (transitional pores), and the macropores.

Micropores have molecular dimensions, the effective radii being less than 2

nm. The adsorption in these pores occurs through volume filling, and there is no

capillary condensation taking place. The adsorption energy in these pores is much

larger compared to larger mesopores or to the nonporous surface because of the

overlapping of adsorption forces from the opposite walls of the micropores. They

generally have a pore volume of 0.15 to 0.70 cm3/g. Their specific surface area

constitutes about 95% of the total surface area of the activated carbon. Dubinin

further suggested that for some activated carbons, the microporous structure can be

subdivided into two overlapping microporous structures involving specific

micropores with effective pore radii smaller than 0.6 to 0.7 nm and the super

micropores showing radii of 0.7 to 1.6 nm. The micropore structure of activated

carbons is characterized largely by the adsorption of gases and vapors and, to a

smaller extent, by small-angle x-ray scattering technique.


11

Mesopores, also called transitional pores, have effective dimensions in the 2

to 50 nm range, and their volume usually varies between 0.1 and 0.2 cm3/g. The

surface area of these pores does not exceed 5% of the total surface area of the

carbon. However, by using special methods, it is possible to prepare activated

carbons that have an enhanced mesoporosity, the volume of mesopores attaining a

volume of 0.2 to 0.65 cm3/g and their surface area reaching as high as 200 m

2/g.

These pores are characterized by capillary condensation of the adsorbent with the

formation of a meniscus of the liquefied adsorbate. The adsorption isotherms show

adsorption desorption hysteresis is which stops at a relative vapor pressure of 0.4.

Besides contributing significantly to the adsorption of the adsorbate, these pores act

as conduits leading the adsorbate molecules to the micropore cavity. These pores

are generally characterized by adsorption-desorption isotherms of gases, by mercury

porosimetry, and by electron microscopy.

Macropores are not of considerable importance to the process of adsorption

in activated carbons because their contribution to the surface area of the adsorbate is

very small and does not exceed 0.5 m2/g. They have effective radii larger than 50

nm, and frequently in the 500 to 2000 nm range, with a pore volume between 0.2

and 0.4 cm3/g. They act as transport channels for the adsorbate into the micro- and

mesopores. Macropores are not filled by capillary condensation and are

characterized by mercury porosimetry.

Figure 1.1: the macropores (a), the mesopores (b) , and the micropores (c)[5].

Thus, the porous structure of activated carbons is tridisperse, consisting of

micro-, meso-, and macropores. Each of these groups of pores plays a specific role

in the adsorption process. The micropores constitute a large surface area and


12

micropore volume and, therefore, determine to a considerable extent the adsorption

capacity of a given activated carbon, provided that the molecular dimensions of the

adsorbate are not too large to enter the micropores. Micropores are filled at low

relative vapor pressure before the commencement of capillary condensation. The

mesopores, on the other hand, are filled at high relative pressures with the

occurrence of capillary condensation. The macropores enable adsorbate molecules

to pass rapidly to smaller pores situated deeper within the particles of activated

carbons. Thus, according to Dubinin, the pattern of porous structure in activated

carbons constitutes macropores opening up directly to the external surface, the

transitional pores branching off from the macropores, and the micropores in turn

branching off from the transitional pores.

1.3. Chemical Structure of Activated Carbon Surface [3]

The crystalline structure of a carbon has a considerable influence on its

chemical reactivity. However, the chemical reactivity at the basal plane sites is

considerably lower than at the edge sites or at defect positions. Consequently,

highly graphitized carbons with a homogenous surface consisting predominantly of

basal planes are less reactive than amorphous carbons. Grisdale and Hennig

observed that the oxidation rates of carbon atoms at the edge sites were 17 to 20

times greater than at the basal plane surface. Similarly, intercalation reactions that

involve dimensional changes to the carbon structure are possible only with highly

graphitized carbons because of their high degree of order.

Activated carbons are almost invariably associated with appreciable amounts

of oxygen and hydrogen. In addition, they may be associated with atoms of sulfur,

nitrogen, and halogens. These heteroatoms are derived from the starting material

and become a part of the chemical structure as a result of imperfect carbonization,

or they become chemically bonded to the surface during activation or during

subsequent treatments. There is also evidence that the carbon can adsorb certain

molecular species such as amines, nitrobenzene, phenols, and several other cationic

species.


13

1.3.1. Carbon-Oxygen Surface Groups

Carbon-oxygen surface groups are by far the most important surface groups

that influence the surface characteristics such as wettability, polarity, and acidity,

and physico-chemical properties such as catalytic, electrical, and chemical

reactivity of these materials. In fact, the combined oxygen has often been found to

be the source of the property by which a carbon becomes useful or effective in

certain respects. For example, the oxygen has an important effect on the adsorption

capacity of carbons for water and other polar gases and vapors, on their ageing

during storage, on the adsorption of electrolytes, on the properties of carbon blacks

used as fillers in rubber and plastics, on the lubricating properties of graphite as

well as on its properties as a moderator in nuclear reactors. In the case of carbon

fibers, these surface groups determine their adhesion to plastic matrices and

consequently their composite properties. According to Kipling, the atoms of oxygen

and hydrogen are essential components of an activated carbon with good adsorptive

properties, and the surface of such materials is to be considered as a hydrocarbon

surface modified at some points by oxygen atoms.

Although the determination of the number and nature of these surface

chemical groups began more than 50 years ago, the precise nature of the functional

groups is not entirely established. The estimations obtained by different workers

using varied techniques differ considerably because the carbon surface is very

complex and difficult to reproduce. The surface groups cannot be treated as

ordinary organic compounds because they interact differently in different

environments. They behave as complex structures presenting numerous mesomeric

forms, depending upon their location on the same polyaromatic frame. Recent

electron spectroscopy for chemical analysis (ESCA) studies have shown that

irreversible transformation of surface groups occurred when classical organic

chemistry methods were used to identify and estimate them. It is Thus, expected

that the application of more sophisticated techniques such as FTIR, XPS, NMR


14

spectroscopy, and radiotracer studies will contribute significantly to a more precise

knowledge about these surface chemical groups.

1.3.2. Characterization of Carbon-Oxygen Surface Groups

Carbons have great tendency to extend this layer of chemisorbed oxygen,

and many of their reactions arise because of this tendency. For example, carbons are

capable of decomposing oxidizing gases such as ozone and oxides of nitrogen,

chemisorbing oxygen. They also decompose aqueous solutions of silver salts,

halogens, ferric chloride, potassium and ammonium persulphate, sodium

hypochlorite, potassium permanganate, potassium dichromate, sodium thiosulphate,

hydrogen peroxide, and nitric acid. In each case, there is chemisorption of oxygen

and the formation of carbon-oxygen surface compounds. Carbons can also be

oxidized by heat treatment in air, CO2, or oxygen. The reaction of activated carbons

with oxygen gas at temperatures below 400C predominantly results in the

chemisorbtions of oxygen and the formation of carbon-oxygen surface compounds,

whereas at temperatures above 400C the decomposition of the surface compounds

and the gasification of the carbon are the predominating reactions.

Figure 1.2: The reactions of activated carbons with oxygen gas

In the case of oxidations in the solution phase, the major reaction is the

formation of the surface compound, although some gasification may also take place

depending upon the strength of the oxidative treatment and the severity of the

experimental conditions. The formation of carbon-oxygen surface compounds using

different activated carbons and carbon black, and using various oxidative treatment

in gaseous and solution phase, has been studied by a large number of investigators


15

and has been very well reviewed. Thus, we merely point out that carbons have a

tendency to pick upon oxygen, at least to some extent under all conditions.

Carbons have an acid-base character. This fact has encouraged many

investigators to devote their research effort to understand the cause and mechanism

by which a carbon acquires an acid or a base character. Several theories (e.g., the

electrochemical theory of Burstein and Frumkin, the oxide theory of Shilov and his

school, the chromene theory of Garten and Weiss, and the pyrone theory of Voll

and Boehm, have been proposed to explain the acid-base character of carbons.

These theories and the related work have been elaborately reviewed and critically

examined in several review articles. It is now well accepted that the acid-base

character of carbons is developed as a result of surface oxidation and depends on

the history of formation and the temperature of oxidation.

Three types of carbon-oxygen surface groups (acidic, basic, and neutral)

have been recognized. The acidic surface groups are very well characterized and are

formed when carbon is treated with oxygen at temperatures up to 400C or by

reaction with oxidizing solutions at room temperature. These surface groups are

thermally less stable and decompose on heat treatment in vacuum or in an inert

atmosphere in the temperature range of 350 to 750C evolving CO2. These acidic

surface groups render the carbon surface hydrophilic and polar in character and

have been postulated to be carboxylic, lactone, and phenolic groups.

The basic surface oxygen groups are much less characterized and are

obtained when a carbon surface, freed of all surface oxygen groups by heat

treatment in vacuum or in inert atmosphere at 1000C, and after cooling to room

temperature, is contacted with oxygen gas. Garten and Weiss proposed a pyrone-

type structure for basic surface groups, which has also been referred to as a

chromene structure. This structure has a heterocyclic oxygen-containing ring with

an activated = CH2 or = CHR (R is an alkyl group) group. According to Voll and

Boehm, the oxygen atoms in the pyrone-like structure are located in two different

rings of a graphitic layer. Out of the two differently bonded oxygen atoms on the


16

basic surface sites, one decomposes into CO2 and CO at 900C and the other at

1200C.

Figure 1.3: Functional groups of basic character: (a) chromene, (b) pyrone-

like.

The neutral surface oxygen groups are formed by the irreversible

chemisorption of oxygen at the ethylene type unsaturated sites present on the carbon

surface. The surface compound decomposes into CO2 on heat treatment. The

neutral surface groups are more stable than the acidic surface groups and start

decomposing in the temperature range 500 to 600C and are removed completely

only at 950C.

Figure 1.4: Model of a fragment of an oxidized activated carbon surface.

1.4. Applications of Activated Carbons [3]

Activated carbons are excellent and versatile adsorbents. Their important

applications relate to their use in the adsorptive removal of color, odor, taste, and

other undesirable organic and inorganic impurities from drinking waters; in the


17

treatment of urban ground and industrial waste water; solvent recovery; air

purification in inhabited spaces such as restaurants, food processing, and chemical

industries; for the removal of color from various types of sugar syrups, oils, and

fats; in thepurification of many chemical, food, and pharmaceutical products; in

respirators forwork under hostile environments; and in a variety of other gas-phase

applications. They are increasingly being used in the field of hydrometallurgy for

the recovery of gold, silver, and other inorganics, and as catalytic and catalyst

supports. Their use in medicine and health applications to combat certain types of

bacterial ailment and for the removal of certain toxins is well known. These

applications of activated carbon are of interest to most economic sectors and

concern areas as diverse as the food, pharmaceutical, chemical, petroleum, mining,

nuclear, automobile, and vacuum industries. Nearly 80% of the total activated

carbon is consumed for liquid-phase applications, where both the granulated and

powdered forms of activated carbon are used. For gas-phase applications,

granulated carbon is usually the choice. However, with the commercial production

of fibrous activated carbons in the form of fibers and fabric, these materials may be

in preference, especially for water treatment processes, because they produce low

hydrodynamic resistance to flow and can easily be molded into any shape in the

adsorption equipment.


18

Chapter 2. Experiments and methods

2.1. Research objective

First, activated carbon was modified by using oxidizing agent KMnO4/

H2SO4 at the difference concentration of acid and KMnO4 at room temperature in

order to modify the activated carbons surface from hydrophobic surface to

hydrophilic surface, from reducing surface to oxidized surface and have ability to

adsorb ion (material AC1).

Then, we titrate modified activated carbon by NaOH to determine total of

acid site on modified activated carbon.

In order to alter the activated carbons surface, we mobilized MnO2, Fe(OH)2,

Al(OH)3 into the surface of activated carbon after being modified to enhance the ion

adsorption ability of activated carbon (material AC-2). After that, the material AC-2

will be divided into 3 parts, the first part is submerged into the NaOH 0.5M solution

to form the alkaline form, the second part is submerged into H2SO4 0.5M solution to

make materials AC-2 has acidic form. In this study, we mainly focus on the

treatment of arsen in the form of AsO4- and cation NH4

+ in aqueous solution based

on the adsorption, ion exchange.

2.2. Equipment and chemical

2.2.1. Equipments

Hood, oven

A laboratory shaker

50.00ml, 100.00 ml volumetric flask.

10.00ml, 5.00ml, 20.00ml, 50.00ml pipet.

20ml glass tube.

100ml, 50ml, 25ml beakers.


19

filter paper.

flask.

2.2.2. Chemical subtance

Table 2.1: Chemical substances

No Name Quality

1 Activated

carbon

TraBac Joint Stock Company, size

0.51mm

2 NaOH Chinese, PA.

3 HCl Chinese, 35%, PA

4 KI Chinese, 10%, PA

4 SnCl2 Chinese, saturated, PA

5 HgBr2 Chinese, PA.

6 Pb(CH3COO)2 Chinese, PA.

7 KNaC6H4O4 Chinese, PA.

8 KMnO4 Chinese, 0.025M, PA.

9 H2SO4 Chinese, 0.1M, PA.

2.3. Material

AC-1:

Oxidating completely total activated carbons surface by 0.025M

KMnO4/H2SO4 solution until the oxidation process completes and the amount of

KMnO4 excess (color of solution is violet)


20

The resulting mixture was separated, the solution was titrated by H2C2O4 to

find out the remaining amount of KMnO4. The solid part was washed by acid HCl

(pH=3) to clean out MnO2 (if it exists), then the activated carbon was washed by

distilled water to clean out SO42-

and Cl-

(check by BaCl2 solution and AgNO3

solution). After that, it was dried in the oven at temperature of 1100C. At this

temperature, if acid remains, it will be decomposed totally. The resulting sample is

the totally oxidized activated carbon, called AC-1 material.

AC-2:

Weighing of 5g FeSO4.7H2O (1% Fe in comparing to activated carbon), 1.7g

MnSO4.2H2O (the ratio between Fe and Mn is 2:1), 2.46g Al2(SO4)3, after that,

dissolving this mixture in 110ml of water. Adding 99g of AC-1 to this solution and

vacuuming from 1 to 2 hours.

The resulting mixture was precipitated NaOH/ H2O2 solution until the pH is

6-8 (note that the solution should not be too alkaline because MnO2, Al2O3 could be

dissolved). The mixture is annealed in 8 hours, then it washed by distilled water to

clean out SO42-

(check by BaCl2 solution) and. After that, it was dried at

temperature of 1000C to obtain the material AC-2.

AC-2(B) and AC-2(A):

Mashing material AC-2 in NaOH solution with the concentration in range

from 0.1-1M (in this experiment, the concentration of NaOH solution is 0.5M) in 1

hour. Washing the material until the pH was 7-8. Then it was dried naturally or

dried at temperature of 60oC. The obtaining material had alkaline form (Material

AC-2(B)).

Similarly, to create the material having acid form material AC-2(B), the

material AC-2 was masked in H2SO4 solution with concentration of 0.5M in 1 hour.

Washing this material until pH was 6 and ion SO42-

was cleaned out. The obtaining

material was dried naturally or dried at temperature of 60oC.


21

2.4. Method of examining features of denatured activated carbon

2.4.1. Determination of KMnO4 consumption and total electrons exchanged

Take 1g activated carbon and add a 120mL of the 0.025M KMnO4 solution,

shake it in 3 hour. Then, titrate the excess potassium permanganate by using the

standard oxalic acid solution. The end point is the point at which color change from

violet to colorless. Repeat 3 times and calculate total electrons exchanged.

Formula for total electrons exchanged:

electron exchanged =electron donor = electron acceptor

2.4.2. Determination of acid groups in activated carbon and oxidized

activated carbon

On the surface of activated carbon, there are weak and strong acid functional

groups that attend to the process of making surface complex and exchanging with

the ions in the wastewater. Therefore, the determination of the number of acid

functional groups on the surface of activated carbon plays an important rule in

assessing ion adsorption ability of resulting activated carbon.

There are 2 methods to determine the total number of acid centers on the

surface of activated carbon and oxidized activated carbon.

The first method is neutralizing by the excess amount of NaOH 0.018M. The

remaining alkali is titrated by 0.021M HCl solution with phenolphthalein indicator.

However, this method can cause error because the activated carbon can adsorb

phenolphthalein indicator.

The total mole of acid group per gram is determined by the below formula:

=( ) 10

3

(/)

Where:


22

V volume of NaOH solution used to neutralize (ml)

C0, C concentration of original and equilibrated NaOH solution (M)

respectively.

m weight of activated carbon (g).

The second method is titrating method by alkali, measuring pH with glass

electrode. This method has higher accuracy. Steps of this method are as follows:

weighing 1g of activated carbon and put to a flask. Pouring each volume of 0.01M

NaOH solution and then shaking in 15 minutes in order to neutralize the acid center

with the strong alkali, after that measuring pH. Continuing these steps until the pH

is nearly unchanged.

The total number of acid centers is determined by the below formula:

a=V.C.10-3

.R /m. (*)

Where:

C concentration of original NaOH solution (M) .

m weight of activated carbon (g).

V the volume of NaOH solution used to neutralize (ml)

R - Avogadro number

2.5. Method for determination of ions in solution

2.5.1. Determination of ammonium concentration

Ammonium concentrations in water are determined by color measurement

method with Nessler reagent.

General principle: In the alkaline environment, NH4+

reacts with Nessler

reagent and become a complex with the color from yellow to brown, depended on

the concentration of ammonium in the solution.


23

The limiting factors: Iron hinders the determination, and it is eliminated by

signet salt or comlexon(III). When the organic compounds, alcols, aldehyt, cloramin

which can react with Nessler reagent exist in solution, they need to be distilled to

separate ammoniac before determining. If water is muddy, it should be processed by

solution ZnSO4 25%.

Determining method: Take 5 ml of sample, add 0.2 ml of Segnete and 0.5 ml

of Nessler. After 10 minutes, measure the optical adsorption at the wavelength of

420 nm.

Building ammonium standard curve: Create the ammonium solution with

concentration of 5mg/l from the ammonium solution with concentration of 1g/l.

Pour distilled water and 5mg/l ammonium solution into the test tube with the

corresponding amount as shown in the below table:

Table 2.2: The standard curve of NH4+

V NH4+ (ml) 0 1 2 3 4 4.5 5

V H2O (ml) 5 4 3 2 1 0.5 0

Figure 2.1: Calibration curve of ammonium

y = 0.1848x + 0.2698 R = 0.9983

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6

Ab

s

C(g/ml


24

2.5.2. Determination of Arsenic concentration

1. Arsenic standard solution

Dissolve 1.32 g of As2O3 ( PA ) in 10 mL H2O which was dissolved 4 g

NaOH , using 6M HCl solution transferred to weak acidic ( pH 5-6 ) , after which

the flask 1000ml distilled water added to As a solution outlined 1g / L ( 1000ppm ) .

Get a 5 mL 1000 ppm As for 1000ml flask and dilute norms we obtain a

solution Arsenic 5 ppm (5000 ppb). Liquid phase is finished bottled polyethylene.

2. 10 % KI solution

Weighing 10g of KI and dissolving it with 30 ml of distilled water in a cup.

Pouring this solution into 100ml flask which is rinsed by distilled water. Rinsing the

cup 3 times and then adding water to reach the outline norm, then shaking. The

obtaining KI solution was stored in a color bottle to avoid the light, with sealed

buttons.

3. SnCl2 solution

Putting 20 tin beads into 100 ml of 1:1 HCl solution and storing this mixture

in a glass bottle with sealed buttons. After 48 hours, obtaining SnCl2 solution.

During the experiment, if the tin is dissolved, adding some beads to remain SnCl2

solution.

4. Paper impregnated with Pb(CH3COO)2

Weigh 10 g of Pb(CH3COO)2 and dissolved in 100ml of distilled water.

Liquid phase are completed on filter paper impregnated, dried naturally. The paper

is cut to the size of 60 80 mm and stored in colored glass jars, sealed.

5. Mercury-impregnated paper

Dissolve 4g HgBr2 (PA) in 100 ml of ethanol 95 %. Liquid phase are

completed on filter paper impregnated with crude not contain arsenic. Let it dry

naturally. HgBr2 impregnated paper cut to size 3x150 mm and stored in colored

glass jars, sealed


25

6. 1:2 HCl solution

The 1:2 HCl solution is diluted from the condensed HCl solution with the

ratio between condensed HCl and distilled water of 1:2. Liquid phase completed in

containers sealed glass button.

The principle of the method

After the samples were acidified, AsH3 gas generated by the reaction of

arsenite with hydrogen newborn ( Zn + HCl in the reactor ) will draw up , go

through the jar wrapped with lead acetate impregnated paper, and then reacted with

HgBr2 on impregnated paper , impregnated paper HgBr2 switch from white to

yellow -brown. The height of the color bar is proportional to the average

concentration of arsenic in

Reaction equation:

AsO43-

+ 2I--+ 4H+ = AsO2

2- + I2 + 2H2O

AsO22-

+ Zn + 14H+ = 2AsH3 + Zn

2+ + H2O

AsH3+ 3HgBr2 = As(HgBr2)3 +3HCl

7. Process of analysis

Obtaining a precise amount of sample to be analyzed (V = 50ml) in 100ml

volumetric flask. Then add 25ml, respectively, and 5 drops of 1:2 HCl to remove

the entire KI As (V) to As (III). Let stand about 15 minutes. The amount of

liberated I2 makes the solution is yellow. Give 4-5 drops of saturated SnCl2 into the

bottle and shake to remove the form I- I2. HgBr2 soaked shredded paper size 3x150

mm was put into a small glass tube rubber buttons. Next soaked paper wrapped

Pb(CH3COO)2 in the top of the bottle. 3 grams of zinc particles in, and seal the

paper. Insert the glass tube containing impregnated paper into the jar HgBr2. AsH3

gas generated by the reaction of arsenite with hydrogen produced will draw up new,

impregnated paper HgBr2 move from white to yellow -brown. To react for 60

minutes then take out HgBr2 impregnated paper about color measurement height.

The amount of arsenic in the sample will be proportional to the height h.


26

Table 2.3: The standard curve of arsenic

C(ppb) 100 300 500 700 900 1000

h(mm) 6.75

16.4

28.1

37.5

48.1

52.4

Figure 2.2: Calibration curve of As

2.6. Method of calculating the adsorption capacity of the material

2.6.1. Investigation of ion adsorption capacity[1][7]

Model calculations for the adsorption technique, commonly used is

Langmuir or Freundlich equation. Langmuir proposed his theory by making

following assumption:

1. Fixed number of vacant or adsorption sites are available on the

surface of solid [6].

2. All the vacant sites are of equal size and shape on the surface of

adsorbent [6].

y = 0.0513x + 1.6342 R = 0.9991

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200

hei

ght

(mm

)

C(ppb)


27

3. Each site can hold maximum of one gaseous molecule and a constant

amount of heat energy is released during this process [6].

4. Dynamic equilibrium exists between adsorbed gaseous molecules and

the free gaseous molecules [6].

Where A (g) is unadsorbed gaseous molecule, B(s) is unoccupied metal

surface and AB is Adsorbed gaseous molecule [6].

5. Adsorption is monolayer or unilayer [6].

Langmuir adsorption theory is described by a equation:

.

Where:

: the amount of adsorption in units of moles adsorbate per mass

adsorbant and the maximal adsorption (mg/g)

C : the solution concentration at equilibrium

b: Langmuir equation coefficients (determined from experiments)


28

To determine the constants in the Langmuir equation, we can write the

equation in the form of:

Line performing C / m depends on C is a line with slope 1 / m and cutting

vertical axis at 1 / bm.

Thus:

2.6.2. Investigation of adsorption equilibrium time

Arsen: Weighing 6 AC samples, each sample 0.5 g, into a 250 ml

Erlenmeyer flask. Add 50 ml As solution 1ppm. Bring it on the machine,

shaking during continuous turn: 1h, 2h, 3h, 4h, 5h, 6h. After that take part in

the solution and analyze the remaining amount of As. From the obtained

results, we determined the time to reach equilibrium adsorption of As of

materials.

Ammonium: Preparing 8 samples of each material, each sample weigh of

0.5 g, into an 250 ml Erlenmeyer flask. Add 50 ml of 5mg/l ammonium


29

solution and shaking continuously on the machine. Just after 30 minutes,

taking 1 sample analyzed the remaining amount of ammonium.

2.6.3. Determination of the maximal adsorption

Arsenic: Preparing 7 samples of each material, each sample weigh of 0.5 g

into a 250 ml Erlenmeyer flask. Add 100 ml arsenic solution with

concentrations of 10, 20, 30, 40, 70, 100, 150 mg/l. The mixture was shaking

for 4 hours. Then extract the solution and dilute so that the concentration of

the final As solution was approximately 1ppm and determine arsenic

remaining amount.

Ammonium: Preparing 8 samples of each material, each sample weigh of 0.5

g into a 250 ml Erlenmeyer flask. Adding 100 ml ammonium solution with

concentrations of 5, 10, 20, 30, 40, 70,80, 100 mg / l. Shaking the mixture

for 2 hours. Then extracting the solution and diluting so that the remaining

ammonium amount of approximately 5 ppm and determining remaining

amount.


30

Chapter 3. Results and Discussion

3.1. Determination of KMnO4 consumption of activated carbon

The average result of three parallel experiments is showed in table 3.1.

Table 3.1: Consumption of KMnO4 for oxidation of activated carbon

Total initial amount of

KMnO4 (mmol/g)

Exceed amount of

KMnO4 (mmol/g)

Consumed amount of

KMnO4 (mmol/g)

3 2.265 0.735

Based on the experimental result above, every one gram activated carbon

required 0.735 mmol of KMnO4 to reduce almost reductive groups, which have

oxidation reduction potential lower than that of KMnO4 (about +1.54 V). In acidic

condition, MnO4- reduced into Mn

2+, therefore, 1 g activated carbon has received

the sum of electrons in this reaction as follow:

Total electrons exchanged = 0.735 x 5 x 6.023.1023

= 22.135.1023

.

3.2. Preliminary determination of total acid center on activated

carbons surface

The total number of acid center on the surface of oxidized activated carbon

was determined by the neutralizing titration method with NaOH solution. Because

NaOH is a strong alkali, it can react with almost acid functional groups. Therefore,

the result is the total number of acid center on the surface of oxidized activated

carbon. The data of titration curve is in the below table:


31

Table 3.2: pH of original and oxidized activated carbon with corresponding

volume of NaOH 0.01M

Oxidized AC

V (mL) pH

0 5.67

2.5 6.58

5 6.88

10 7.14

15 7.28

17.5 7.42

20 7.47

25 7.71

30 7.75

32.5 7.85

35 7.95

37.5 8.03

40 8.13

42.5 8.2

45 8.34

47.5 8.45

52.5 8.89

60 9.29

65 9.56

70 9.65

75 9.71

80 9.8

85 9.93

90 10.01

95 10.09

100 10.13

105 10.17

110 10.24

120 10.38

Original AC

V (mL) pH

0 3.85

5 6.57

10 9.75

15 10.27

20 10.53

25 10.71

30 10.83

35 10.85

50 10.95

60 11.03

70 11.11

80 11.21

90 11.28

100 11.33


32

From this table we have the graph:

Figure 3.1: Titration curve of AC and denatured AC

According to the titrating result, it can be that the titrating curve of original

AC has a big jump from 0 to 10 ml, after 40 ml, the pH of solution is nearly

unchanged. It proves that all acid centers, even weak acids having pKa>10 were

neutralized. The total mol of acid and total number of acid centers can be

calculated. Applying the formula (*), the number of acid centers in 1g of original

activated carbon is 2.4 x 1020

(center/g). With oxidized activated carbon (material

AC-1), the titrating curve has 3 curling ranges corresponding with 3 general

intensity levels of acid groups that were created after oxidizing the activated carbon.

These ranges are from 0.0 to about 20 ml of NaOH; from 30 ml to about 65 ml and

from 65 ml to 120 ml of 0.01 M NaOH solution. However, after 100 ml of 0.01M

NaOH solution, the pH value of solution is nearly unchanged. It proves that all acid

centers, even weak acids having pKa>10 were neutralized. The number of acid

centers in 1g of oxidized activated carbon is 6.1020

(center/g) calculated according

to formula (*).

0

2

4

6

8

10

12

0 50 100 150

pH

Volume(ml)

oxidized AC

unoxidized


33

3.3. Investigation of Arsenic adsorption capacity of the material

3.3.1. Investigation of Arsenic adsorption equilibrium time

Because of the similar characteristic of materials, in this part, only one

material was chosen to examine the the maximal adsorption equilibrium time As of

material. It was AC-2(B) material.

We have the result table below:

Table 3.3: The data of arsenic adsorption equilibrium time of material AC2(B)

Sample M1 M2 M3 M4 M5

Time 1h 2h 3h 4h 5h

h(mm) 14 12.2 11.4 10.2 7.2

CAs excess (ppm) 4.272732 4.376979 4.423311 4.492809 4.666554

Figure 3.2: The Arsenic adsorption equilibrium time

Examining similarly other materials gave the result that the maximal

adsorption equilibrium time of materials is from 4 to 5 hours. Therefore, in other

similar experiments, As was adsorbed in 5 hours continuously.

4.2

4.3

4.4

4.5

4.6

4.7

0 1 2 3 4 5 6 7

C a

dso

p

t(h)


34

3.3.2. Determination of the maximal arsenic adsorption capacity

3.3.2.1. Material AC-1

The examining results of 7 AC-1 samples with the arsenate solution with

concentration from 5ppm, 10ppm, 20ppm, 30ppm, 40ppm, 60ppm, 70ppm are

shown in the below table:

Table 3.4: The examination data of material AC-1

Co(ppm) H(mm) Cf(ppm) Q(mg/g) Cf/Q

5 11.3 1.42724421 0.71455116 1.99739962

10 11.6 2.941361 1.4117278 2.08351851

20 12.3 6.28812741 2.74237452 2.29294991

30 14.6 9.52521718 4.09495656 2.32608503

40 10.1 12.5349903 5.49300193 2.28199271

60 18 23.9732143 7.20535714 3.32713755

70 23.1 31.3573842 7.72852317 4.05735785

Figure 3.3: The Langmuir adsorption isotherm of AC-1

From the graph, we can determine the maximal arsenic adsorption of

material AC-1:

Qmax = 1/0.1237 =8.084 mg/g or 0.058mmol/g

y = 0.1237x + 1.4389 R = 0.9699

0

1

2

3

4

5

6

7

0 5 10 15 20 25 30 35 40 45

Cf/

Q

Cf


35

This result shows that the oxidized activated carbon has ability of adsorbing

arsenic in form of ion AsO43-

was not appropriate for its surface. Although the

adsorption ability is not high, adsorption capacity is quite low, there is a great

improvement in comparing with the un-oxidized activated carbon. This allows to

predict that: it is possible to modify the surface of activated carbon by oxidizing

factor to change the hydrophobic surface of Tra Bac activated carbon in order to

change the structure and adsorption ability, specially arsenic adsorption ability.

3.3.2.2. Material AC-2

The examining results of 7 AC-2 samples with the arsenate solution with

concentration from 10ppm, 30ppm, 50ppm, 70ppm,100ppm,120ppm, 150ppm are


Table 3.5: The examination data of material AC-2

Co H(mm) Cf(ppm) Q(mg/g) Cf/Q

10 4 0.493726 1.901255 0.259684

30 12 2.038127 5.592375 0.364448

50 19 3.389479 9.322104 0.363596

70 28.9 5.300676 12.93986 0.409639

100 13.2 11.34894 17.73021 0.64009

120 17.2 15.20994 20.95801 0.725734

150 30 27.56515 24.48697 1.125707

Figure 3.4: The Langmuir adsorption isotherm of AC-2

y = 0.0312x + 0.2639 R = 0.9948

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30

Cf/

Q

Cf


36

From the graph, we can determine the maximal arsenic adsorption of

material AC-2:

Qmax = 1/0.0312 =32.05 mg/g or 0.23mmol/g

The results show that arsenic adsorption ability in form of AsO43-

of AC-2

material is 4 times higher than AC-1 and much higher than AC-0. It proves that

adding MnO2, Fe2O3, Al2O3 to the surface of activated carbon after modifying

increases arsenic adsorption ability of activated carbon. We can see that there are

many other oxides and compounds that can be added to the activated carbons

surface to change the structure and adsorption ability of activated carbon. It can be

applied in field of processing hazardous materials in water such as AsO43-

.

3.3.2.3. Material AC-2(B)

The examining results of 9 AC-2(B) samples with the arsenate solution with

concentration from 10ppm, 30ppm, 50ppm, 70ppm, 80ppm, 100ppm, 120ppm,

150ppm, 170ppm are shown in the below table:

Table 3.6: The examination data of material AC-2(B)

Co H(mm) Cf(ppm) Q(mg/g) Cf/Q

10 8.5 1.021839 1.795632 0.569069

30 14.85 3.882481 5.223504 0.743271

50 24.6 6.70584 8.658832 0.774451

70 35.5 9.86221 12.02756 0.819968

80 42 11.74445 13.65111 0.860329

100 11.2 14.12765 17.17447 0.822596

120 14.8 19.34001 20.132 0.96066

150 20 26.86897 24.62621 1.091072


37

170 27 37.0041 26.59918 1.391175

Figure 3.5: The Langmuir adsorption isotherm of AC-2(B)

From the graph, we can determine the maximal Arsenic adsorption of

material AC-2(B):

Qmax = 1/0.02 =50 mg/g or 0.359 mmol/g

3.3.2.4. Material AC-2(A)

The examining results of 7 AC-2(A) samples with the arsenate solution with

concentration from 10ppm, 20ppm, 50ppm, 60ppm, 70ppm, 80ppm, 100 ppm are


Table 3.7: The examination data of material AC-2(A)

Co h Cf Q Cf/Q

10 7.3 0.565396 1.886921 0.299639

20 15.3 1.337597 3.732481 0.358367

50 19.8 3.543919 9.291216 0.381427

60 25.1 4.567085 11.08658 0.411947

70 30.4 5.590251 12.88195 0.43396

80 39.5 7.347008 14.5306 0.505623

y = 0.02x + 0.6027 R = 0.9579

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30 35 40

Cf/

Q

Cf


38

100 17.3 15.30647 16.93871 0.903638

Figure 3.6: The Langmuir adsorption isotherm of AC-2(A)

From the graph, we can determine the maximal Arsenic adsorption of

material AC-2(A):

Qmax = 1/0.0401 = 24.937 mg/g or 0.179 mmol/g

Through examining the Arsenic adsorption capacity in form of AsO43-

of

material, it can be seen that the As adsorption ability of material AC-2(B) is 6 times

higher than material AC-1; 1.56 times higher than material AC-2 and 2 times higher

than material AC-2(A). It show that modifying to have alkaline form of activated

carbon improves the As adsorption ability in form of ion AsO43-

.

3.4. Investigation of ammonium adsorption capacity of the material

3.4.1. Investigation of ammonium adsorption equilibrium time

The examining results show that ammonium adsorption capacities of

material AC-1 and AC-2 are quite low (hardly adsorbed). It allows predict that: the

oxidation of the activated carbons surface does not improve the ammonium

adsorption ability of materials. Therefore, I continues examining material AC-2(A)

and AC-2(B).

y = 0.0401x + 0.2517 R = 0.963

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10 12 14 16 18

Cf/

Q

Cf


39

Because of the similar characteristic of materials, in this part, only one

material was chosen to examine the the maximal Ammonium adsorption

equilibrium time of material. It was AC-2(B) material.

We have the table:

Table 3.8: The data of ammonium adsorption equilibrium time of material

AC-2(B)

t(h) Abs Cf Chp

0.5 0.903 3.42640693 1.57359307

1 0.901 3.41558442 1.58441558

2 0.837 3.06926407 1.93073593

2.5 0.833 3.04761905 1.95238095

3 0.822 2.98809524 2.01190476

3.5 0.823 2.99350649 2.00649351

Figure 3.7: The Ammonium adsorption equilibrium time

Examining similarly other materials gave the result that the maximal

adsorption equilibrium time of materials is from 1.5 to 2 hours. Therefore, in other

similar experiments, As was adsorbed in 2 hours continuously.

3.4.2. Determination of maximal ammonium adsorption of material AC2(B)

0

0.5

1

1.5

2

2.5

0 1 2 3 4

C a

ds

(pp

m)

t (h)


40

3.4.2.1. Material AC-2(B)

The examining results of 8 AC-2(B) samples with the ammonium solution

with concentration from 5ppm, 10ppm, 20ppm, 30ppm, 50ppm, 70ppm, 90ppm,

100ppm are shown in the below table:

Table 3.9: Langmuir examining results of material AC-2(B)

Co Abs Cf Q Cf/Q

0 0 0 0 0

5 0.678 2.208874 0.279113 7.91392

10 0.751 5.207792 0.479221 10.86721

20 0.689 11.34199 0.865801 13.1

30 0.608 18.30087 1.169913 15.64292

50 0.899 34.04762 1.595238 21.34328

70 1.203 50.49784 1.950216 25.89345

90 0.763 66.72078 2.327922 28.66109

100 0.827 76.46104 2.353896 32.48276

Figure 3.8: The Langmuir adsorption isotherm of AC-2(B)

From the graph, we can determine the maximal Ammonium adsorption of

material AC-2(B):

Qmax = 1/0,2986 =3.453 mg/g or 0.191 mmol/g

y = 0.2959x + 9.455 R = 0.9731

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60 70 80

Cf/

Q

Cf(ppm)


41

3.4.2.2. Material AC-2(A)

The examining results of 6 AC-2(A) samples with the ammonium solution

with concentration from 5ppm, 10ppm, 15ppm, 20ppm, 30ppm, 40ppm are shown

in the below table:

Table 3.10: Langmuir examining results of material AC-2(A)

C

Cf q Cf/q

0 0 0 0 0

5 0.835 3.05844156 0.01941558 157.525084

10 0.956 6.18867244 0.03811328 162.375769

15 0.619 9.44805195 0.05551948 170.175439

20 0.74 12.7218615 0.07278139 174.795539

30 0.987 18.8636364 0.11136364 183.146736

40 0.785 28.0952381 0.11904762 230

Figure 3.9: The Langmuir isotherm of AC-2(A)

From the graph, we can determine the maximal Ammonium adsorption of

material AC-2(A):

Qmax = 1/2.7226 =0.36729 mg/g or 0.0204 mmol/g

y = 2.7226x + 143.96 R = 0.9033

0

50

100

150

200

250

0 5 10 15 20 25 30


42

Through examining the ammonium adsorption capacity in form of NH4+

of

materials AC-1, AC-2, AC-2(A) and AC-2(B), it can be seen that the ammonium

adsorption ability of AC-2(B) is the best (Qmax = 3,453 mg/g) while material AC-1

and AC-2 adsorb ammonium hardly. The reason may be that the surface of material

AC-2(B) has alkaline form that increases the ammonium adsorption ability of AC-

2(B). The result is that the maximal adsorption capacity of AC-2(B) is 10 times

higher than AC-2.

The results show that materials AC-1, AC-2, AC-2(B) and AC-2(A) can

adsorb anion AsO43-

better than cation NH4+. It can be an important advantage of

modified activated carbon and open a new direction for researching using activated

carbon as adsorbent for small size particles which other methods cannot adsorb.


43

CONCLUSION

In this reseach, I focus on the modification of the activated carbons surface

by using strong oxidizers and adding Mn(IV), Fe(III) and Al to the surface of

activated carbon after modifying in order to create the materials having stronger

adsorpting center. The obtaining results are:

1. In my initiating investigation the total electron exchanged and total acid

groups on the oxidized activated carbon were determined. The number of

electrons exchanged is 2.2131024

electrons per 1.00 gram and the total

number of acid center is about 61020

centers per 1.00 gram.

2. We have carried out the oxidized reduction surface of activated carbon by

KMnO4 solution in acidic H2SO4 to modify the reduction surface of

activated carbon into the oxidized surface, transforming from a hydrophobic

surface to hydrophilic surface (materials AC -1)

3. We have conducted a study by adding MnO2, Fe2O3, Al2O3 on the surface of

activated carbon after oxidizing. We have created a new hybrid material

(AC-2 material).

4. Modifying AC-2 surface by NaOH solution to gain a material which has

alkaline surface (material AC-2(B)) and by H2SO4 solution to gain a material

which has acidic (material AC-2(A)).

5. Carried out examining, determining that the adsorption capacity for arsenic

of materials AC-1, AC-2, AC-2(B) and AC-2(A) are 8.084mg/g; 32.05

mg/g; 50 mg/g; 24.937 mg/g respectively in the normal condition. The

maximal equilibrium time is 5h. Determining that the adsorption capacity for

ammonium of materials AC-2(A), AC-2(B) are 0.36729 mg/g; 3.453mg/g

respectively in the normal conditions, the maximal equilibrium time is 2h.

The results show that modified activated carbon has better adsorption ability

for the toxic compounds in form of anion in comparing with cation.


44

REFERENCES

[1] V Ngc Ban(2007), Gio trnh thc tp Ha l, Nh xut bn i hc Quc

gia H Ni.

[2] F. Julien, M. Baudu and M. Mazet (1998), Relationship between chemical and

physical properties of activated carbon, Wat. Res, 32(11), pp. 3414-3424.

[3] Roop Chand Bansal, MeenakshiGoyal (2005), Activated Carbon Adsorption,

Taylor & Francis Group, LLC.

[4] S. Biniak, G.Szymaki, J. Siedlewski, A. Swiatkowski (1997), The

characterization of activated carbons with oxygen and nitrogen surface group,

Carbon, 35(12), pp. 1799-1810.

[5] Shaobin Wang, Z.H.Zhu, Anthony Coomes, F. Haghseresht,G.Q.Lu (2004),

The physical and surface chemical characteristics of activated carbons and the

adsorption of methylene blue from wastewater, Journal of Colloid and Interface

Science.

[6] http://en.wikipedia.org/wiki/Activated_carbon

[7] http://www.chemistrylearning.com/langmuir-adsorption-isotherm/

kltn newest Thủy.pdf

Documents

Transcript of kltn newest Thủy.pdf