CHAPTER-3 SOLVENT EXTRACTION STUDIES OF RUTHENIUM(III...

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Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular weight amine Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 26 CHAPTER-3 SOLVENT EXTRACTION STUDIES OF RUTHENIUM(III) USING HIGH MOLECULAR WEIGHT AMINE 3.1 Introduction Ruthenium is a scarce element that is found in about 10 -8 % of the earth’s crust. It is present in much larger amounts in chondrite and, especially, in iron meteorites ((1-6) x 10 -4 %). It usually occurs in association with other platinum group metals [1]. Ruthenium is a rare and polyvalent hard white transition metal. Small amount of Ru can increase the hardness of platinum and palladium. The corrosion resistance of titanium is increased markedly by the addition of a small amount of ruthenium [2]. Ruthenium is a versatile catalyst. This is used to remove H 2 S from oil refineries [3]. Ruthenium was also suggested as a possible material for microelectronics because its use is compatible with semiconductor processing techniques [4]. Due to its hardness and corrosion resistance, ruthenium is used to coat electrodes in the chloralkali process which produces chlorine and caustic soda for a wide range of industrial and domestic applications. In the future, the use of ruthenium in alloys for aircraft turbine blades will help to reduce the CO 2 impact of air travel on the environment. If current prototypes are successful, their high melting points and high temperature stability will allow for higher temperatures and, therefore, a more efficient burning of aircraft fuel [5]. Recently, platinum metals, especially ruthenium and its chlorocomplexes, have been much used in the catalytic oxidation of some organic compounds. Organometallic ruthenium carbene and allenylidene complexes are efficient catalysts for olefin metathesis [6]. Ruthenium complex shows greater resistance to hydrolysis and has more selective action on tumors. Ruthenium and its alloys also have a widespread application in jewellery [1]. In radiochemistry, the interest lies in the separation of rhodium from ruthenium since rhodium is daughter of ruthenium by beta decay [7].

Transcript of CHAPTER-3 SOLVENT EXTRACTION STUDIES OF RUTHENIUM(III...

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             26

CHAPTER-3

SOLVENT EXTRACTION STUDIES OF RUTHENIUM(III) USING

HIGH MOLECULAR WEIGHT AMINE

3.1 Introduction

Ruthenium is a scarce element that is found in about 10-8 % of the

earth’s crust. It is present in much larger amounts in chondrite and, especially,

in iron meteorites ((1-6) x 10-4 %). It usually occurs in association with other

platinum group metals [1].

Ruthenium is a rare and polyvalent hard white transition metal. Small

amount of Ru can increase the hardness of platinum and palladium. The

corrosion resistance of titanium is increased markedly by the addition of a

small amount of ruthenium [2]. Ruthenium is a versatile catalyst. This is used

to remove H2S from oil refineries [3]. Ruthenium was also suggested as a

possible material for microelectronics because its use is compatible with

semiconductor processing techniques [4]. Due to its hardness and corrosion

resistance, ruthenium is used to coat electrodes in the chloralkali process which

produces chlorine and caustic soda for a wide range of industrial and domestic

applications. In the future, the use of ruthenium in alloys for aircraft turbine

blades will help to reduce the CO2 impact of air travel on the environment. If

current prototypes are successful, their high melting points and high

temperature stability will allow for higher temperatures and, therefore, a more

efficient burning of aircraft fuel [5]. Recently, platinum metals, especially

ruthenium and its chlorocomplexes, have been much used in the catalytic

oxidation of some organic compounds. Organometallic ruthenium carbene and

allenylidene complexes are efficient catalysts for olefin metathesis [6].

Ruthenium complex shows greater resistance to hydrolysis and has more

selective action on tumors. Ruthenium and its alloys also have a widespread

application in jewellery [1]. In radiochemistry, the interest lies in the separation

of rhodium from ruthenium since rhodium is daughter of ruthenium by beta

decay [7].

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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The growing use of ruthenium in widely different fields has made it

necessary to develop simple, inexpensive and sensitive method for its

separation and determination. To recover and separate metals from low-value

resources, such as low-grade ores and recycled materials, the solvent extraction

process is the best option [8].

3.2 Review of literature for liquid-liquid extractive separation of

ruthenium(III)

In recent years various reagents have been studied for liquid-liquid

extraction of ruthenium(III). The reageats such as 2-mercaptobenzimidazole

used as extractant for ruthenium(III) in n-butanol [9], 3-hydroxy-2-methyl-1-

phenyl-4-pyridone [10], Cyanex 921[11], and Cyanex 923, Cyanex 471,

Cyanex 272, LIX 54, LIX860N-I [12] are reported for solvent extraction.

Also, some organophosphorus compounds like triphenylphosphine

(TPP) extracts chlorocomplex of ruthenium(III) in 1,2-dichloroethene only in

presence of SnCl2 [13]. Method requires heating before extraction and

prolonged equilibrium time (60 min) for quantitative recovery of ruthenium.

Bis (2-ethylhexyl) phosphoric acid [14, 15] and tributyl phosphate [16-19]

extract nitrosyl-ruthenium complex in dodecane or kerosene or solvesso-100

[18, 19]. This method was used for extraction of U, Zr and Ru from nuclear

fuel reprocessing but needs longer time, about 6 months for the formation of

extractable ruthenium complex. Octyl (phenyl)-N-N-di-isobutyl

carbamylmethylphosphine oxide was used as extractant for actinides and

fission products in dodecans from nitric acid media [20]. However, extraction

of ruthenium was not quantitative and equilibrium time was more (1 hr.).

Solvent extraction by high molecular weight amine (HMWA) has

become increasingly popular in recent years for studying metal complexes.

These are known as liquid anion exchangers which uniquely combine some of

the advantages of liquid-liquid extraction and ion exchange. It was further

observed that the acid binding properties of HMWA depend on the fact that

acid salts of these bases are essentially insoluble in water while they are readily

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             28

soluble in hydrocarbon solvents [21]. High molecular weight amine (HMWA)

reported for ruthenium(III) extraction are Alamine 336 [22], Alamine 300,

Aliquat 336 [12], tri-iso-octylamine [23], trioctylamine oxide [24], The

thiocyanate complex of ruthenium(III) was extracted with bis (2-

ethylhexyl)amine in 1,2-dichloroethene, this method was used for

determination of ruthenium in substrates for microelectronics applications but

optimal pH range was narrow [25]. A synergistic extraction of chlorocomplex

of ruthenium(IV) with trioctylamine [26] in mixed solvents like

tributylphosphate thenoyltrifluoroacetone and 1-phenyl-3-methyl-4-benzoyl-

pyrazolidone was reported. N-Octylamine [27] was reported for the extraction

of ruthenium(IV) from hydrochloric acid media. The solvent extraction of

ruthenium from hydrochloric acid media has been carried out using N,N’-

Dimethyl-NN’-dicyclohexylmalonamide (DMDCHMA) dissolved in 1,2-

dichloroethane [28]. Trinonylamine [29] extracts ruthenium(IV) in kerosene

from hydrochloric acid madia. In this method synergistic effect on ruthenium

extraction was observed in presence of dimonolyamine (DNA), aliquat and

methyl iso butyl ketone (MIBK). Alkylaniline [30] extracts chlorocomplex of

ruthenium in toluene and method was applied for the extraction of noble

metals. A primary amine i.e. dodecylamine [31] was reported for the

extraction of ruthenium(III) in mixed solvents from hydrochloric acid media

but the extraction efficiency was independent on the concentration of extractant

and method was time consuming. Octylaniline hydrochloride [32] and

alkylaniline hydrochloride [33, 34] extracts ruthenium from chloride or sulfate

medium in toluene. p-Octylaniline [35,36] in presence of bis(2-ethyl-hexyl)

dithiophosphate extract ruthenium in hydrochloric acid media. The method was

found to be applicable for extraction of ruthenium from copper- nickel ore and

also for extraction of noble metals [33-35]. Ruthenium(III) was extracted by

tetra-nitroaniline [37] in nitric acid media. The extracted ruthenium(III) was

backstripped with 10 % NaOH and method was selective in presence of large

amount of iridium. But, method needs heating before extraction and also

multiple extraction for recovery of ruthenium. Trialkylamine [38] extracts

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ruthenium(III) in kerosene from nitric acid media. The method can be used for

selective separation of ruthenium(III) from uranium.

The oxygenated and hydrocarbon solvents like chloroform [39], carbon

tetrachloride [40], MIBK [41], paraffin oil [42], mixtuer of isoamyl alcohol and

isobutyl methyl metone [43] have also been used as extractants for ruthenium.

Ruthenium was extracted in chloroform from hydrochloric acid and method

was suitable for determination of ruthenium in iron meteorites. However,

method is selective in presence of NaIO4 [39]. Carbon tetrachloride extracts

ruthenium in sulphuric acid media and method was applicable for the

separation of ruthenium from osmium but extraction is highly selective only in

presence of oxidizing agents [40]. MIBK used as extractant for ruthenium(III)

in presence of hydrochloric acid media. The extraction of metals from

thiocyanate media has been successful in applied chemistry. Ruthenium(III) is

separated by purex process using paraffin oil in nitric acid medium but it is

necessary to oxidise Ru to RuO4 by addition of ceric nitrate before extraction

[42]. Mixture of isoamyl alcohol and MIBK in 1:1 ratio extract ruthenium in

large excess of platinum but iridium interferes in the extraction procedure [43].

During last few years substituted thioureas have been reported for the

solvent extraction of ruthenium. N,N-dialkyl-N’-benzoyl-thioureas [44] extract

ruthenium(III) in Solvesso 150. Method was applicable for extraction and

separation of platinum group metals from solution containing base metals. But

optimal pH range is narrow. N-mono- and N,N-di-substituted benzoylthioureas

[45] extract ruthenium(III) from chloride media in toluene but the method

demands large volume of the extracting solvent to affect the quantitative

recovery of metal. Attempts have also been made to selectively separate

ruthenium(III) from associated elements with P-50 oxime [46], di(2-

ethylhexyl) sulfoxide [DHSO] [47]. The various investigated systems are

presented in tabular form in Table 3.1 to review the literature in terms of

various extractants used and special characteristics regarding those systems.

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Development of new extraction system for extraction of ruthenium(III)

especially in weak organic acid solutions is a topic of great interest. The goal of

this work is to study the extraction properties of n-octylaniline with respect to

noble metal such as ruthenium(III) from weak organic acid media. In this work,

n-octylaniline-malonate system was studied to investigate the extraction of

aqueous ruthenium(III) solution as a function of various parameters. The

proposed method is used for rapid and selective separation of ruthenium(III)

form associated elements in their binary mixtures. It is also tested for

separation and determination of ruthenium(III) from various real samples like

catalysts and synthetic mixture sample.

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Table 3.1 Summary of methods for solvent extraction of ruthenium(III)

System Aqueous

phase Organic

phase Special features

Ref.No.

2-mercaptobenzimidazole

pH-2.0 n-Butanol Rapid method for quantitative extraction of ruthenium(III).

9

3-hydroxy-2-methyl-1-phenyl-4-pyridone

pH-6.5 to 7.0

Dichlorome- thane

Heating of the aqueous phase before extraction.

Separation of ruthenium from large amount of palladium(II) and rhodium(III).

10

Cyanex 921 HCl

Toluene Ruthenium extraction study in presence or absence of tin(II) chloride.

Ruthenium separates from Os, Ir.

11

Cyanex 923, Cyanex 471, Cyanex 272, LIX 54, LIX860N-I, Alamine 300, Aliquat 336

HCl - Separation of ruthenium from iridium, rhodium.

12

Ttriphenylphosphine (TPP)

HCl 1-6 M + SnCl2

1,2-Dichloro- ethane

Shaking for 60 min and heating before extraction.

Method applicable for extraction of platinum group metals.

13

Bis (2-ethylhexyl) phosphoric acid

HCl, pH 4.05

Isopar M Method applicable for extraction of rhodium and iridium.

14, 15

HCl, 0.5 M; thiourea pH 4.5.

Isopar M

Ruthenium was backstripped with 1M HCl

Ruthenium recovery 40.8 %

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             32

Tributyl phosphate (TBP)

HNO3, 2 M

Solvesso-100

Extraction of ruthenium in presence of gamma irradiated sulphoxides

Method applied for extraction of U, Zr, and Ru.

16

HNO3, 3 M

Dodecane The acid solution was aged in a dark box for 6 months in order to equilibrate reaction between ruthenium complex.

Ruthenium was backstripped with 0.5 M Na2SO3 Solution.

17

HNO3

n-Dodecane, Kerosene

Ruthenium extracting as nitrosyl-ruthenium.

18, 19

Octyl (phenyl)-N-N-di-isobutyl carbamylmethyl- phosphine oxide (CMPO)

HNO3 Dodecane Extraction of ruthenium in presence of TBP.

Method applicable for Pm(III), U(VI), Pu(IV), Am(III), Zr(IV), Ru(III), Fe(III), Pd(II).

The nature of the species has been suggested.

20

Alamine 336 HCl Kerosene Extraction of ruthenium (III) increased with increasing concentration of HCl up to 5 M

Method applicable for separation of Ir(III), Rh(III), Ru(III) with the help of strripant.

22

Tri-iso-octylamine HCl, 4 M Carbontetra- chloride

SCN-, CN-, S2-, S2O32-,

EDTA, bromide, sulphite nitrite, iodide, Ag+ interfere in extraction.

Salting out agents used in separation of other metals

23

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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Trioctylamine oxide HCl CCl4 Ruthenium chloro complexes

occurs during extraction

24

Bis (2-ethylhexyl)amine

HCl 0.3 M; NaSCN, 0.15- 0.7 M, pH, 2

1,2-Dichloro- ethene

Method used for the determination of ruthenium in substrates for microelectronics applications.

25

Trioctylamine HCl, 4 M Mixed solvents system

Synergistic extraction of Ru(IV) with solvents like TBP, thenoyltrifluoroacetone and 1-phenyl-3-methyl-4-benzoyl-pyrazolidone-5

26

N-octylamine 1 M HCl Xylene Method required large amount of extractant.

27

N,N’-Dimethyl-NN’-dicyclohexylmalonami-de (DMDCHMA)

HCl 1,2-Dichloro- ethene

Method applicable for extraction of PGMs

28

Tri-nonyl-amine (TNA) HCl > 3 M

Kerosene Synergistic extraction of Ru(IV) in presence of TNA and MIBK.

29

Alkylaniline HCl 2-3 M

Toluene Method applicable for extraction of precious metals

30

Dodecylamine HCl > 6 M

CCl4 : isoamyl alcohol (9:1)

Recovery of Ruthenium(III) 80 %

Shaking time 20 min

31

Octylaniline hydrochloride

H2SO4 Toluene Extraction of ruthenium(III) in presence of 20 % NaCl

32

Alkylaniline hydrochloride

HCl Toluene Method was used for extraction of PGMs except osmium and determination by AAS.

Extraction in presence of petroleum sulphides.

33

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HCl, 6 M Toluene Extraction in presence of

petroleum sulphide. Method was used for

extraction of PGMs, gold in copper-nickel ore and related plant materials

34

p-octylaniline

HCl 2-4 M

Toluene Extraction of ruthenium in presence of bis(2-ethyl-hexyl) dithio- phosphate.

Method applied for extraction of Ru from Copper-Nickel sulphide ore.

35, 36

Tetra-nitroaniline HNO3,

1 % Tetra- nitroaniline

Ruthenium(III) was backstripped with 10 % NaOH.

Ruthenium was separated from solution containing large amount of iridium.

37

Trialkylamine HNO3 Kerosene The method can be used for selective separation from uranium.

38

Chloroform HCl, NaIO4

Chloroform Method was suitable for determination of ruthenium in iron meteorites.

39

Carbon tetrachloride H2SO4, 6 M

CCl4 Ruthenium was separated from osmium

40

MIBK HCl, 2-3 M; KSCN

MIBK Method applicable for extraction for PGMs.

Ruthenium recovery Ru > 95 %

41

Paraffin oil HNO3 Paraffin oil Ruthenium(III) selectively separated from purex process

42

Isoamyl alcohol: MIBK

HCl, 6 M Isoamyl alcohol: MIBK

Method applicable for extraction of Ru, Ir, and Rh in large excess of platinum.

43

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             35

N,N-dialkyl-N’-benzoyl-thioureas

pH, 3 Solvesso 150

Coextraction Cu and Fe, re-extraction with 4 M H2SO4.

Method applied for separation of PGMs from Cu, Fe, Ni, Co and Zn.

44

N,N-di-substituted benzoylthioureas

HCl, 0.1- 6 M

Toluene Method used for the solvent extraction of platinum metals.

Efficiency of extraction increases as concentration of ligand increases.

45

P-50 oxime HNO3

4 M Escaid 100 Method applicable for

extraction of palladium. 46

Di(2-ethylhexyl) sulfoxide [DHSO]

HNO3

Kerosene The extraction abilities

for U,Th and some fission products are presented

47

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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3.3 Experimental

3.3.1 Apparatus

Elico digital spectrophotometer model l2 Chemito 215D with 1 cm

quartz cells was used for absorbance measurements and pH measurements were

carried out using an Elico digital pH-meter model LI-127. All weighing

operations were done by using Tapson’s analytical single pan balance model

200 T having 0.001 gm accuracy.

3.3.2 Reagents

Standard ruthenium(III) solution

A stock solution of ruthenium(III) was prepared by dissolving 1 g of

ruthenium chloride hydrate (Johnson Matthey, UK) in dilute analar HCl (1 mol

dm-3) and diluting to 250 mL with water and standardized [48]. A working

solution of 200 µg/mL was made by diluting the stock solution with water.

4’-ChloroPTPT

1-(4’-Chlorophenyl)-4,4,6-trimethyl-(1H,4H)-pyrimidine-2-thiol

(4’-ChloroPTPT) was prepared by the method of Mathes [49-52] and used for

the specrophotometric determination of ruthenium(III).

Standard solution of diverse ions were prepared by dissolving AR grade

reagents in water or dil HCl. All the organic solvents were used after double

distillation. All chemicals used were of AR grade.

n-Octylaniline

The reagent n-octylaniline was prepared by the method of Pohlandt’s

[53] and its 0.1 M solution was prepared in xylene. Aqueous solutions were

prepared with water. Double distilled water was used through the experimental

study.

3.3.3 General procedure for extraction and determination of

ruthenium(III)

To an aliquot containing 200 µg ruthenium(III) in 25 mL volumetric

flask a sodium malonate was added to get the concentration of solution 0.05 M.

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The pH of the resulting solution was adjusted to 3.5 with dilute HCl and NaOH

solution. The aqueous solution was shaken with 10 mL 0.1 M n-octylaniline in

xylene for 5 min. After the phase separation, the organic phase was stripped

with the 4:1 combination of 2 % of NaCl and 1 M HCl.

The back extracts were evaporated to moist dryness and dissolved in

minimum amount of aqua regia and evaporated with two 2 mL portions of

concentrated HCl to remove oxides of nitrogen. The residue was dissolved in

0.1 M and ruthenium(III) was determined spectrophotometrically by

4’-chloroPTPT at λ max = 605 nm [54]. All the experiments were repeated on

an average five times.

The percentage extraction, % E, was calculated using expression

% E = (metal extracted/ metal taken) ×100 …..(3.1)

and the distribution ratio, D, was calculated using expression

D = (% E / (100 – % E)).Volume aqueous phase/Volume organic phase) (3.2)

3.4 Results and discussion

3.4.1 Effect of pH

The effect of pH on the percentage extraction of ruthenium(III) was

studied in the pH range of 0.5 to 10 with 0.1 M n-octylaniline in xylene

(Table 3.2). The Fig. 3.1, shows that the extraction of ruthenium(III) was found

to be quantitative in the pH range 3.1 to 4.0. Hence, all extractions of

ruthenium(III) were carried at pH 3.5.

3.4.2 Effect of reagent concentration

Extraction of ruthenium(III) was carried out with various concentrations

of n-octylaniline in xylene (Table 3.3). To optimize the extraction condition,

other parameters like pH, period of equilibration and diluent were kept

constant. The extraction was found to be increased with increasing reagent

concentration. The extraction of ruthenium(III) was quantitative in the range

0.09 M to 0.13 M of n-octylaniline in xylene (Fig 3.2). However, 10 mL of

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Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             38

0.1 M n-octylaniline in xylene was recommended for general extraction

procedure.

3.4.3 Effect of weak organic acid concentration

The extraction of ruthenium(III) was carried out at pH 3.5 with 0.1 M

n-octylaniline in xylene in the presence of varying concentrations of sodium

malonate, sodium succinate, and sodium salicylate as weak acid media

(Table 3.4). The extraction of 200 μg ruthenium(III) was found to be

quantitative in the range of 0.04 M - 0.055 M for sodium malonate and further

increase in malonate concentration there was decrease in extraction. The

extraction of ruthenium(III) was found to be incomplete in the salicylate and

succinate media. Thus, 0.05 M concentration of malonate was used throughout

the experimental work (Fig 3.3).

3.4.4 Effect of diluents

In this study, extraction of ruthenium(III) was carried out by using various

aromatic and aliphatic organic diluents. It was found that the extraction of

ruthenium(III) was quantitative with xylene, toluene and in benzene while there

was incomplete extraction in methyl isobutyl ketone (93.04 %), n-butyl

alcohol (42.2 %) and no extraction in amyl alcohol, chloroform,

1,2-dichloroethane, carbon tetrachloride and amyl acetate. Throughout the

experiment xylene was used as solvent (Table 3.5).

3.4.5 Effect of stripping agents

Ruthenium(III) from organic phase was stripped with three 10 mL

portions of various stripping agents (Table 3.6). Ruthenium(III) was

quantitatively stripped with 30 mL 2 % NaCl and 10 mL 1 M HCl. However,

percentage recovery of ruthenium(III) from organic phase was found to be

incomplete with strippants like acetate buffer, sodium hydroxide, ammonia and

potassium hydroxide. In recommended procedure, 30 mL 2 % NaCl and

10 mL 1 M HCl was used for the complete stripping of loaded organic phase.

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3.4.6 Equilibration time

The period of equilibration was varied from 1 to 18 min (Table 3.7). The

extraction of ruthenium(III) was quantitative over a period of 3 min shaking of

the solution, but with prolonged shaking over 12 min (Fig. 3.4) there was

decrease in the percentage extraction of ruthenium(III) due to the dissociation

of ion-pair complex. Thus, equilibration time for 200 μg ruthenium(III)

extraction was kept about 5 min throughout the study.

3.4.7 Extraction behavior of ruthenium(III) as a function of metal loading

capacity

Varying concentrations of ruthenium(III) (50 – 2000 μg) were extracted

with 10 mL portions of 0.1 M n-octylaniline in xylene from 0.05 M sodium

malonate media. It was observed that extraction of ruthenium(III) was

quantitative upto 500 μg (Table 3.8).

3.4.8 Effect of aqueous to organic volume ratio

The effect of contacting the different volume ratios of aqueous to

organic phase was studied (Table 3.9). The results indicate that the preferred

aqueous/organic (A/O) phase ratio in this study must be in between 1:1 to 4:1.

Extraction decreases after ratio of 4:1 due to the less availability of reagent.

However, in the recommended procedure, the phase ratio was maintained at

2.5:1.

3.4.9 Stoichiometry of extracted species

Attempts were made to ascertain the nature of the extracted complex

species using log D - log C plots. The graphs of log D[Ru(III)] against

log C[n-octylaniline] at fixed sodium malonate concentration (0.05 M ) were found

to be linear and having slopes of 1.0 and 0.99 value at pH 5.0 and 6.0,

respectively (Fig. 3.5). Also plot log D[Ru(III)] against logC[Malonate] at fixed

n-octylaniline concentration (0.1 M) were linear and slope values were found to

be 2.0 and 1.75 at pH 5.0 and 6.0, respectively (Fig. 3.6). The probable

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composition of extracted species is calculated to be 1:2:1 (Metal: Acid:

Extractant). The possible mechanism of extracted species appears to be

protonated n-octylaniline which forms cationic species as

[CH3(CH2)7C6H4NH3] +(org) while malonate (bidentate ligand) combines with

ruthenium(III) to form anionic species as Ru(C3H2O4)-2(aq) and both of them

associate to form ion-pair of the type [CH3(CH2)7C6H4NH3+ Ru(C3H2O4)-

2](org)

and being neutral constitutes extractable species.

The possible mechanism of ion- pair complex is as follow:- CH3(CH2)7C6H4NH2(org) + H+ CH3(CH2)7C6H4NH3

+(org) (3.3)

Ru3+(aq)

+ 2C3H2O4-(aq) Ru(C3H2O4)2

-(aq) (3.4)

CH3(CH2)7C6H4NH3+

(org) + Ru(C3H2O4)2-(aq) [CH3(CH2)7C6H4NH3

+Ru(C3H2O4)2-](org) (3.5)

3.4.10 Effect of diverse ions The effect of a large number of foreign ions on the extraction of

200 µg/mL of ruthenium(III) with n-octylaniline was investigated following the recommended procedure. The tolerance limit of individual foreign ions was set so that error in percentage recovery was not more than ±2 %. Rh(III) and Pd(II) were masked with 25 mg tartrate and Ir(III) with 25 mg oxalate. Au(III) was masked with 10 mg bromide (Table 3.10). The species showing interference in the procedure were ascorbate, thiourea, citrate and thiocyanate.

3.5 Applications 3.5.1 Separation of ruthenium(III) from associated metal ions

The method permits separation and determination of ruthenium(III) from binary mixtures containing Os(VIII), Pt(IV), Cu(II), Fe(III), Co(II), Ni(II), Se(IV) and Te(IV). Ruthenium(III) was separated from these associated metal ions, under the optimum extraction conditions of ruthenium(III) where, all the added metal ions were remained quantitatively in aqueous phase from which they were determined spectrophotometrically by standard methods [55-60]. Ruthenium(III) from organic phase was stripped and estimated spectrophotometrically by 4’-chloroPTPT method (Table 3.11).

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Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             41

Under the optimum extraction condition of ruthenium(III), some metals like Rh(III), Pd(II), Ir(III) and Au(III) were co-extracted. Rh(III) and Pd(II) were masked with 25 mg tartrate. Ir(III) and Au(III) were masked with 25 mg oxalate and 10 mg bromide respectively. The masked metal ions remained in the aqueous phase, they were demasked with perchloric acid followed by hydrochloric acid. The residue was dissolved in 10 mL water and evaporated to moist dryness to remove trace of acid completely. The residue containing Rh(III), Pd(II), Ir(III) and Au(III) were determined spectrophotometrically by standard methods [54-59].

3.5.2. Separation of ruthenium(III) from Ternary mixture The selectivity of extraction was also achieved by the use of a suitable masking agent for added metal ion. When a ternary mixture containing ruthenium(III), palladium(II) and rhodium(III) was extracted from 0.05 M malonate acid with 10 mL of 0.1 M n-octylaniline in xylene at pH 3.5 by masking Pd(II) and Rh(III) with tartrate (25 mg), it was found that ruthenium(III) was extracted; whereas palladium(II) and rhodium(III) remained unextracted. Ruthenium(III) was strripped with 2 % of NaCl and 1 M HCl (4:1) and estimated as per the recommended procedure [54].

The aqueous phase containing tartrates of palladium(II) and rhodium(III) and excess of malonate were decomposed by the addition of concentrated hydrochloric acid. Then, the solution was adjusted to 0.03 M with sodium malonate. Rhodium(III) was extracted quantitatively with 10 mL of 0.1 M n-octylaniline in xylene at pH 9.0. Rhodium(III) from organic phase was stripped with 1 M hydrochloric acid (2×10 mL) and estimated spectrophotometrically with stannous chloride–potassium iodide method [55]. The aqueous phase containing malonate was decomposed with concentrated hydrochloric acid and residue extracted into 0.1 M hydrochloric acid. The solution was made to 0.085 M with respect to sodium salicylate. Palladium(II) was extracted with 10 mL of 0.07 M n-octylaniline in xylene at pH 1.5. Palladium(II) from organic phase was stripped with 5 M ammonia (2×10 mL) and estimated spectrophotometrically with 4’-chloroPTPT [54] (Table 3.12).

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3.5.3 Determination of ruthenium(III) from synthetic mixture corresponding to alloys

The proposed method was applied to the extraction and determination of ruthenium(III) from malonate media at pH 3.5 in various ternary mixtures (Table 3.13). Ruthenium(III) was extracted with 0.1 M n- octylaniline in xylene while Pt(IV), Ni(II), Te(IV), Fe(III), Co(II), U(VI) remained unextracted in the aqueous phase. However, Rh(III) and Pd(II) were masked by 25 mg tartrate and Ir(III), Au(III) with 25 mg oxalate and 10 mg bromide respectively. The extracted ruthenium(III) was stripped and determined by 4’-chloroPTPT method spectrophotometrically. 3.5.4 Analysis of ruthenium(III) in catalysts sample Ruthenium(III) activated carbon and alumina (0.1 g) was dissolved in 20 mL aqua regia. The solution was evaporated to moist dryness. Two 5 mL portions of hydrochloric acid were added and evaporated till all the nitric acid was removed. The residue was extracted in 1 M hydrochloric acid. The solution was filtered and the filtrate was diluted to 100 mL. An aliquot of this diluted solution was analyzed for ruthenium(III) content by the proposed method. It was found that there is a good agreement with the certified value (Table 3.14). 3.6 CONCLUSIONS

The extraction equilibria of ruthenium(III) and sodium malonate have been investigated systematically using n-octylaniline in xylene.

The results also demonstrates that n-octylaniline has good extractability for ruthenium(III) in malonate media at pH 3.5 compared with some other high molecular weight amines and organophosphorus compounds. Further, n-octylaniline has good regeneration and loading capacities.

The extraction behavior of ruthenium(III) in presence of other associated elements have been investigated. The method is applied for binary separation of ruthenium(III) from associated transition metals and other rare earths.

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Table 3.2 Extraction of ruthenium(III) as a function of pH Ruthenium(III) = 200 µg Sodium malonate = 0.05 M Aq: org ratio = 2.5: 1 Extractant = 0.1 M n-octylaniline in xylene Strippant = 2 % NaCl +

1 M HCl (4:1)

pH Percentage extraction, (% E) Distribution ratio, (D)

0.5 41.2 1.75

1.0 42.0 1.81

2.0 44.3 1.98

3.0 97.6 101.6

3.1 99.9 2497.5

3.3 99.9 2497.5

3.5* 99.9 2497.5

3.7 99.9 2497.5

3.9 99.9 2497.5

4.0 99.9 2497.5

5.0 83.5 12.65

6.0 70.8 6.06

7.0 27.8 0.96

8.0 26.8 0.91

9.0 25.7 0.86

10.0 22.9 0.74

* Recommended for general extraction procedure

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Table 3.3 Extraction behavior of ruthenium(III) as a function of n-octylaniline concentration

Ruthenium(III) = 200 µg pH = 3.5 Aq: org ratio = 2.5: 1 Sodium malonate = 0.05 M Strippant = 2 % NaCl + 1 M HCl (4:1)

n-Octylaniline, (M) Percentage extraction,(% E)

Distribution ratio, (D)

0.01

20.8 0.65

0.02

21.9 0.70

0.03

26.5 0.90

0.04

36.0 1.40

0.05

46.9

2.20

0.06

54.6 3.00

0.07

61.3 3.95

0.08

91.7 27.62

0.09

99.9 2497.5

0.10*

99.9 2497.5

0.11

99.9 2497.5

0.12

99.9 2497.5

0.13

99.9 2497.5

* Recommended for general extraction procedure

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Table 3.4 Extraction behavior of ruthenium(III) as a function of weak

organic acid concentration Ruthenium(III) = 200 µg pH = 3.5 Aq: org ratio = 2.5: 1 Extractant = 0.1 M n-octylaniline in xylene Strippant = 2 % NaCl +

1 M HCl (4:1)

Acid concentration,

(M)

Sodium malonate Sodium succinate Sodium salicylate

% E D % E D % E D 0.01 48.7 2.37 27.0 0.92 10.0 0.27

0.02 54.1 2.94 45.0 2.04 15.0 0.44

0.03 75.1 7.54 53.7 2.89 24.3 0.80

0.04 99.9 2497.5 60.0 3.75 45.0 2.04

0.045 99.9

2497.5 64.0 4.44 61.0 3.91

0.05* 99.9 2497.5

69.0

5.56

78.0

8.86

0.055 99.9

2497.5 74.0 7.11 84.0 13.12

0.06 96.3 65.06 70.0 5.83 80.0 10.00

0.07 59.7 3.70 62.0 4.07 76.0 7.91

0.08 50.2 2.52 58.3 3.49 72.3 6.52

0.09 30.1

1.07 50.0 2.50 70.0 5.83

0.1 26.2

0.88 48.3 2.33 65.0 4.64

* Recommended for general extraction procedure, D = Distribution Ratio % E = Percentage extraction

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Table 3.5 Extraction of ruthenium(III) with various diluents Ruthenium(III) = 200 µg pH = 3.5 Aq: org ratio = 2.5: 1 Sodium malonate = 0.05 M Strippant = 2 % NaCl + 1 M HCl (4:1)

Solvent Dielectric constant, ε

Amount of Ru(III) extracted, % E

D

Xylene*

2.30 99.9 2497.5

Toluene

2.38 99.9 2497.5

Benzene

2.27 99.9 2497.5

Chloroform

4.80

No extraction

-

Amyl Alcohol

13.90 No extraction -

Amyl Acetate

4.80 No extraction -

Methyl iso butyl ketone (MIBK)

13.10

93.1

33.73

1,2- Dichloro ethane

10.50 No extraction -

n-Butyl alcohol

17.80

42.2

1.82

Carbon tetrachloride

2.24 No extraction -

* Recommended for general extraction procedure, D = Distribution Ratio % E = Percentage extraction

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Table 3.6 Effect of stripping agents on ruthenium(III) extraction Ruthenium(III) = 200 µg pH = 3.5 Aq: org ratio = 2.5: 1 Extractant = 0.1 M n-octylaniline in xylene Sodium malonate = 0.05 M

Strripant

Concentration % E D

HCl

Concentrated (2×10 mL)

99.9

2497.5

HBr

Concentrated (2×10 mL)

99.9

2497.5

2 % NaCl+1 M HCl*

40 mL+10 mL

99.9

2497.5

Ammonia

7 M (3 × 10 mL) 34.5 1.31

Ammonia + NH4Cl

2 M + 3 M (2 × 10 mL)

43.0

1.88

NaOH

1 M (2 × 10 mL)

60.8

3.87

KOH

1 M (2 × 10 mL)

55.8

3.15

H2O

2x10mL

- -

NH4Cl 2%(3x10mL) 26.3 0.89

* Recommended for general extraction procedure % E = Percentage extraction of Ru(III) D = Distribution Ratio.

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Table 3.7 Extraction behavior of ruthenium(III) as a function of equilibrium time

Ruthenium(III) = 200 µg pH =3.5 Sodium Malonate = 0.05 M Aq: org ratio = 2.5: 1 Extractant = 0.1 M n-octylaniline in xylene Strippant = 2 % NaCl +

1 M HCl (4:1)

Time in min

% E D

1 57.9

3.43

2 93.0

33.21

3 99.9

2497.5

4 99.9

2497.5

5*

99.9

2497.5

6 99.9

2497.5

7 99.9

2497.5

8 99.9

2497.5

9 99.9

2497.5

10 99.9

2497.5

12 99.9

2497.5

15 42.0

1.81

18 27.8 0.96

* Recommended for general extraction procedure % E = Percentage extraction of Ru(III) D = Distribution Ratio.

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Table 3.8. Extraction behavior of ruthenium(III) as a function of metal

loading capacity pH =3.5 Extractant = 0.1 M n-octylaniline in xylene Sodium malonate = 0.05 M Aq: org ratio = 2.5: 1 Strippant = 2 % NaCl +

1 M HCl (4:1) Metal concentration in

μg/mL % E D

100

99.9

2497.5

200*

99.9

2497.5

300

99.9

2497.5

400

99.9

2497.5

500

99.9

2497.5

800 78.4 9.07

1000

72.4

6.55

1200

65.3

4.70

1500

50.2

2.52

1800

38.1 1.53

2000

32.2 1.18

* Recommended for general extraction procedure % E = Percentage extraction of Ru(III) D = Distribution Ratio.

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Table 3.9 Extraction of ruthenium(III) as a function of aqueous

to organic volume ratio

Ruthenium(III) = 200 μg pH = 3.5 n-octylaniline = 0.1 M xylene Sodium malonate = 0.05 M Strippant = 2 % NaCl + 1 M HCl (4:1)

* Recommended for general extraction procedure

Aqueous to organic volume ratio

Percentage extraction,

( %E )

Distribution ratio, ( D )

10:10 99.9 2497.5

20:10 99.9 2497.5

25:10* 99.9 2497.5

30:10 99.9 2497.5

35:10 99.9 2497.5

40:10 99.9 2497.5

50:10 77.3 8.51

100:10 55.4 3.10

150:10 43.0 1.88

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Table 3.10 Effect of foreign ions on the extraction of ruthenium(III)

Ruthenium(III) = 200 µg pH = 3.5 Extractant = 0.1 M n-octylaniline Aq: org ratio = 2.5: 1 Sodium malonate = 0.05 M in xylene Strippant = 2 % NaCl + 1 M HCl (4:1)

Tolerance limit, mg Foreign ion added

50 Tartrate, oxalate, fluoride, acetate

25 Bromide, EDTA, Mg(II)

15 Fe(III), Zn(II), Mo(VI), Se(IV), Ba(II),Ce(IV)

10 Ni(II), Co(II), U(VI), iodide, Hg(II)

5 Cu(II), Pb(II), Cr(VI), Bi(III), Te(IV),Cd(II)

2 Phosphate, Tl(I), Ca(II), Al(III), Cr(III), Cd(II),

1 Ag(I), Pt(IV), Os(VIII)

0.5 Rh(III)a,Pd(II) a,Ir(III)b,Au(III)c

a = masked by 25 mg tartrate, b= masked by 25 mg oxalate, c = masked by 10 mg bromide

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Table 3.11 Separation of ruthenium(III) from binary mixtures

Metal ions Amount taken, µg

Average recovery*, %

Chromogenic ligand References

Ru(III)

Pt(IV)

200

300

99.8

99.2

-

SnCl2

[55]

Ru(III)

Pd(II)a

200

200

99.8

99.7

-

4’-ChloroPTPT

[54]

Ru(III)

Ir(III)b

200

100

99.8

98.6

-

SnCl2 - HBr

[55]

Ru(III)

Rh(III)a

200

200

99.8

99.7

-

SnCl2 +KI

[55]

Ru(III) Os(VIII)

200 200

98.0 99.3

Thiourea

[55]

Ru(III)

Au(III)c

200

200

99.8

98.8

-

SnCl2

[55]

Ru(III)

Co(II)

200

1000

99.7

98.8

-

Thiocyanate

[57]

Ru(III)

Ni(II)

200

5000

99.8

98.8

-

DMG

[57]

Ru(III)

Cu(II)

200

2000

99.8

98.8

-

4’-ChloroPTPT

[56]

Ru(III)

Fe(III)

200

1000

99.7

98.8

-

Thiocyanate

[55]

Ru(III)

Se(IV)

200

300

99.8

98.8

-

4’-BromoPTPT

[58]

Ru(III)

Te(IV)

200

200

99.8

98.8

-

4’-BromoPTPT

[59]

* Average of six determinations. a = masked by 25 mg tartrate, b= masked by 25 mg oxalate, c = masked by 10 mg bromide

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Table 3.12 Separation of ruthenium(III) from ternary mixture

Metal ion

Amount taken,

µg

Aqueous phase (25 mL)

Stripping agent

Determination method

Recovery percentage*

Ru(III) 200 0.05 M

malonate

pH = 3.5

2 % NaCl +

1 M (4:1)

4’-

ChloroPTPT

[54]

99.8

Rh(III)a 200 0.03 M

malonate

pH = 9.0

1 M HCl

(2 × 10 mL)

SnCl2 + KI

[55]

99.7

Pd(II)a 200 0.085 M

salicylate

pH = 1.5

5 M

(3 × 10 mL)

4’-

ChloroPTPT

[54]

99.7

a = masked by 25 mg tartrate *= Average of six determination

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Table 3.13. Determination of ruthenium(III) from synthetic mixture

corresponding to alloys

Synthetic mixture Ruthenium

(III) found, µg

Amount of Ru(III) extracted,

%

RSD, % Ions Metal ion

taken, µg Ru(III)

Pd(II)a

Pt(IV)

200

100

100

197.0 98.5 1.5

Ru(III)

Ir(III)b

Rh(III)a

200

100

100

198.7 99.3 0.7

Ru(III)

Ni(II)

Au(III)c

200

100

100

197.0 98.5 1.5

Ru(III)

Co(III)

Fe(III)

200

200

200

198.7 99.3 0.7

Ru(III)

U(VI)

Th(IV)

200

100

100

197.5 98.7 1.3

a = masked by 25 mg tartrate, b= masked by 25 mg oxalate, c = masked

by 10 mg bromide

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Table 3.14. Determination of ruthenium(III) from catalysts

Sample of catalyst (Lancaster make)

Amount of Ru(III) taken, µg

% Recovery of Ru(III)

RSD, %

Ruthenium 5 % on carbon

200 99.7

0.3

Ruthenium 10 % on carbon

200 99.3

0.7

Ruthenium 5 % on alumina

200 99.5

0.5

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0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10

pH

Perc

enta

ge E

xtra

ctio

n (%

E)

Fig. 3.1 Plot of pH versus percentage extraction of ruthenium(III)

(200 μg/mL) from malonate medium (0.05 M) by using

n-octylaniline (0.1 M) as an extractant in xylene with 5 min

shaking time.

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0

10

20

30

40

50

60

70

80

90

100

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13

n-octyaniline (M)

Perc

enta

ge e

xtra

ctio

n (%

E)

Fig. 3.2 Extraction of ruthenium(III) (200 µg/mL) at pH 3.5 from

0.05 M sodium malonate as a function of n-octylaniline

concentration.

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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0

10

20

30

40

50

60

70

80

90

100

0 0.02 0.04 0.06 0.08 0.1

Weak Acid (M)

Perc

enta

ge E

xtra

ctio

n (%

E)

Sodium malonate

Sodium succinate

Sodium salicy late

Fig 3.3 Extraction of ruthenium(III) (200 µg/mL) at pH 3.5 with

0.1 M n-octylaniline as a function of weak organic acid

concentration.

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur                             59

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Time in min.

Perc

enta

ge e

xtra

ctio

n (%

E)

Fig. 3.4 Extraction of ruthenium(III) (200 µg/mL) at pH 3.5 from

0.05 M sodium malonate as a function of equilibration

period.

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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▲ Slope = 1.0 at pH 5

■ Slope = 0.99 at pH 6

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

-1.8 -1.7 -1.6 -1.5 -1.4 -1.3 -1.2 -1.1 -1

Log C [n-octylaniline]

Log

D[R

u(II

I)]

Fig. 3.5 Log-log plot of distribution ratio Log D[Ru(III)] versus

Log C[n-octylaniline] at fixed malonate concentration.

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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▲ Slope = 2.0 at pH 5

■ Slope = 1.75 at pH 6

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1.9 -1.8 -1.7 -1.6 -1.5 -1.4 -1.3 -1.2 -1.1 -1Log C [Malonate]

Log

D[R

u(II

I)]

Fig. 3.6 Log-log plot of distribution ratio Log D[Ru(III)] versus Log C[malonate]

at fixed n-octylaniline concentration.

Chapter 3 – Solvent extraction studies of ruthenium(III) using high molecular  weight amine 

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References

[1] J. A. Rard, Chemistry and thermodynamics of europium and some of its

simpler inorganic compounds and aqueous species, Chem. Rev., 85

(1985) 555.

[2] C. R. Hamond, The elements in Lide, D. R., ed., CRC Handbook of

chemistry and Phycsics, 86th Edition, Boca Raton (FL), CRC press,

2005.

[3] A. D Richards, A. Rodger, Synthetic metallomolecules as agents for the

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