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Chapter 7 Liquidliquid extraction of iridium(III) from malonate media using liquid anion exchanger Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 227 CHAPTER-7 LIQUID-LIQUID EXTRACTION OF IRIDIUM(III) FROM MALONATE MEDIA USING LIQUID ANION EXCHANGER 7.1 Introduction The recovery of platinum group metals (PGMs) such as Ir, Ru and Rh from different matrices is always a challenging task for a chemist. The great aesthetic value and technological importance of these metals has created a never-ending demand [1]. These metals are scarce and have a wide range of industrial applications. The determination of iridium has always been difficult. The extremely inert character of iridium complexes creates a most challenging problem in their separation. Recovery of iridium from spent catalysts and recycling is economically important [2, 3]. In the recycling industry, there are three main categories of refining materials. Primary materials such as gold- /silver ore and PGM concentrates come directly from the mining industry. The most important category, secondary materials, includes chemical/petrochemical catalysts, automotive catalysts, and sweeps or bullion-type material from numerous industrial applications. A third category of growing importance is called “tertiary material” and consists of waste from other precious-metal refining plants, such as insolubles from wet chemical operations, PGM sweeps from Ag/Au refiners, and Ir-/Ru-/ Rh-concentrates [4]. Several extraction methods have been developed for iridium [5-8]. These falls into general types: ion-pair formation or formation of a neutral coordinated complex. The first mechanism is greatly influenced by the charge and the degree of aquation of the complex anion in the aqueous phase. The second mechanism requires a ligand substitution reaction which, for these metals, is very slow; heating the solution containing extractant or use of tin(II) chloride (or bromide) as a labilizing agent is therefore usually necessary. Although working at high temperatures or in the presence of tin salts is acceptable in analytical procedures, the usefulness of such measures in large- scale separations is dubious.

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Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

227

CHAPTER-7

LIQUID-LIQUID EXTRACTION OF IRIDIUM(III) FROM MALONATE MEDIA USING LIQUID ANION EXCHANGER

7.1 Introduction

The recovery of platinum group metals (PGMs) such as Ir, Ru and Rh

from different matrices is always a challenging task for a chemist. The great

aesthetic value and technological importance of these metals has created a

never-ending demand [1]. These metals are scarce and have a wide range of

industrial applications. The determination of iridium has always been difficult.

The extremely inert character of iridium complexes creates a most challenging

problem in their separation. Recovery of iridium from spent catalysts and

recycling is economically important [2, 3]. In the recycling industry, there are

three main categories of refining materials. Primary materials such as gold-

/silver ore and PGM concentrates come directly from the mining industry. The

most important category, secondary materials, includes chemical/petrochemical

catalysts, automotive catalysts, and sweeps or bullion-type material from

numerous industrial applications. A third category of growing importance is

called “tertiary material” and consists of waste from other precious-metal

refining plants, such as insolubles from wet chemical operations, PGM sweeps

from Ag/Au refiners, and Ir-/Ru-/ Rh-concentrates [4].

Several extraction methods have been developed for iridium [5-8].

These falls into general types: ion-pair formation or formation of a neutral

coordinated complex. The first mechanism is greatly influenced by the charge

and the degree of aquation of the complex anion in the aqueous phase. The

second mechanism requires a ligand substitution reaction which, for these

metals, is very slow; heating the solution containing extractant or use of tin(II)

chloride (or bromide) as a labilizing agent is therefore usually necessary.

Although working at high temperatures or in the presence of tin salts is

acceptable in analytical procedures, the usefulness of such measures in large-

scale separations is dubious.

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

 

228 

7.2 Review of literature for liquid-liquid extractive separation of

Iridium(III)

High molecular weight amines (HMWAs) were first used as extractants

by Smith and Page [9]. The extraction of Iridium(III) from hydrochloric acid

and hydrobromic acid with 5 % tri-iso-octylamine solution in carbon

tetrachloride has been studied [10]. A liquid-liquid extraction of iridium(IV)

from chloride solution was studied under different condition of aqueous and

organic phase concentration using alamine-336 [11-15] as an extractant. The

extraction of iridium from its chloride solution was carried out using

commercially available solvent extraction reagents alamine 300 [15] and

aliquat 336 [15, 16]. Liquid-liquid extraction of iridium(III) and separation of

it from other platinum group metals (PGM) from Cl2/HCl leaching of the ores

or concentrations converted into thiourea eluate resin were studied, with high

molecular weight tertiary amines as extractants [17]. The use of

N-n-octyaniline [18] for the extraction of iridium(III) from malonate media was

studied at pH 8.5. Iridium(III) extracted in the organic phase was stripped with

2 M hydrochloric acid and was determined spectrophotometrically by stannous

chloride-hydrobromic acid method at 385 nm. Carbonyl-chloride complexes of

iridium extracted with tri-octylamine (TOA) [19] in isoamyl alcohol. The

extraction of iridium with 4-(non-5-yl)pyridine (NP) [20] was investigated.

Spectroscopic studies indicate that the extracted species is an ion pair. 4-

Octylamino pyridine [21] was used for determination of iridium(III) by

extraction and atomic emission spectrometry with inductively coupled plasma

source. Ideal conditions for extraction of iridium(III) with

2-mercaptobenzothiazole [22-25] into organic solvent have been established.

The stoichiometry of metal to reagent has been evaluated and an Ir192

radiotracer study of [25] of iridium extraction from greater than 1 M HCl acid

has been determined. The substituted thioureas such as N,N'-Dipyridylthiourea

[26] and N,N-diethyl-N'-benzoylthiourea (DEBT) [27] have been used for

solvent extraction of iridium(III). Also N-benzoyl-NN’-dihexyl thiourea [28]

and N-mono-and N,N-di-substituted benzoylthiourea [29] are used for

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

229

extraction of iridium(III). A method was developed for solvent extraction

separation of trace amounts of iridium(III) from noble metal mixture by

thiobenzanilide [30,31]. N-o-tolyl-α-thiopicolinamide [31] and N-phenyl-5-

ethyl-α-thiopicolinamide [31] were used for separation of iridium from other

noble metals by extraction. Extraction of iridium was with 1,3-mono-

thiodicarbonyl [1-carbonyl-3-thioxo] compounds [32] in the presence of

labilizing agents at 85oC temperature from slight acidic media in to chloroform.

However, in a single extraction with chloroform, upto 92 % extraction of

iridium(III) was found from technical chloride solutions. The chloroform

extraction of iridium from 0.1-8 M sulphuric acid in the presence of potassium

ethyl xanthate [33] has been studied. Depending on the acid concentration,

iridium was partly extracted. Complexation and solvent extraction of iridium

with di-propyle sulfide [34] was studied by means of IR, UV, and PMR

spectroscopy. The solvent extraction of iridium(IV) from hydrochloric acid

solution by some dialkyl sulfoxides [35] of the types R2SO, RR'SO and R'2SO,

where R = alkyl and R' = cycloalkyl, was investigated. Solvent extraction of

iridium(III) and iridium(IV) chloride complexes from hydrochloric acid and

chloride solution by a sorbent MITKhAT [36] containing sulfur and nitrogen

was studied. The most probable mechanism of sorption and the complexation

of an iridium complex formed were proposed.

The extraction of iridium(III) from its chloride solution was carried out

using different commercially available solvent extraction reagents such as

cyanex 921 [15], cyanex 923 [15, 37-39], cyanex 471 [13, 37], cyanex 272,

LIX 54 [15], LiX-860N-I [15] and tri-butyl phosphate [15, 40-41]. The

distribution coefficients for the iridium were determined under different

concentrations of Cl-and H+ ions in the aqueous phase [15]. The splitting of a

system from biphasic to triphasic was studied in the liquid-liquid extraction of

Ir(IV) and HCl using cyanex 923 (C923) [38]. Solvent extraction of

iridium(III) with bis-(2-ethyl-hexyl) hydrogen phosphate (HDEHP) from

thiourea chloride [42] chloride media [43] was investigated. Iridium(III)

extracted was only 11.5 %. Separation and refining of iridium(III) by

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

 

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continuous solvent extraction with trioctyl phosphine oxide [44] has been

studied with high sensitivity. Extraction of iridium with triphenylphosphine

(TPP) [45] in 1,2-dichloroethane from hydrochloric acid medium has been

examined. Addition of stannous chloride as labilizing agent makes possible a

group separation of platinum metals. Identification is made with benzidine,

which is oxidized by iridium(IV) to a blue compound. Iridium(III) was very

efficiently removed from solutions containing rhodium(III) and a number of

metals ions by extracting the Triphenyl propylphosphonium salt [46] of the

iridium(III) chlorocomplex into chloroform. Interference of Pd(II), Pt(IV) and

Os(IV) is prevented by preliminary extraction of same reagent.

A new method for the separation and spectrophotometric analysis of

iridium by biphasic extraction system of n-propyl alcohol-sodium chloride –

water [47] was studied. The method was used for the determination of iridium

from Pt-Pd-Ir alloy samples. pH effect was studied on solvent extraction of

iridium(III) sulfates with N-octyl, N,N-dioctyl aniline and N,N,N-trioctyl

anilinium O,O-di(iso-propyl)dithiophosphates [48]. Solvent extraction behavior

of iridium(III) with salicylhydroxamic acid (SHA) [49] in isobutanol from

aqueous chloride solution was studied and compared with similar extraction

behavior of rhodium(III) and ruthenium(III). The formation of ion-pairs of

iridium(III) with pyruvic acid acylhydrazones and cyanine dyes, derivative of

1,3,3-trimethyl-3H-indolium [50] was studied. Iridium(III) could be determined

by this technique in synthetic mixtures in the presence of rhodium. Solvent

extraction of iridium by α-n-nonylpyridine-N-oxide (NPO) [51] from chloride,

sulfate, perchlorate, and nitrate solution was examined. NPO effectively

separates Pt and Ir by extraction from 0.5-1.0 M HCl. N-Hexyl iso-octylamide

[52] was used as an extractant for separation of iridium(IV) from rhodium(III).

Water was the most efficient stripping agent for reverse extraction of

iridium(IV). Iridium(III) was separated from a large excess of platinum by its

extraction with isoamyl alcohol-isobutyl methyl ketone [53] mixture graphite

furnace atomic absorption spectrometry using the method of standard addition

was then used to determine the metals with satisfactory precision and accuracy.

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

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In present investigations, extraction behavior of iridium(III) using

n-octylaniline, a high molecular weight amine in toluene as an extractant was

carried out in presence of malonate media. The extraction system was

developed by checking various physicochemical parameters such as effect of

pH, extractant concentration, diluents, equilibrium period. The conventional

slope analysis method was employed for analysis of species formed in organic

phase. Also effect of various foreign ions on the extraction of iridium(III) was

studied and tolerable amount of each ion was detected. The studies also

extended to separate the iridium(III) from associated elements.

The various investigated systems are presented in tabular form in table

7.1 to review the literature in terms of various extractants used and special

characteristics regarding those systems.

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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Table 7.1 Summary of methods of solvent extraction of iridium(III)

System Aqueous phase

Organic phase Special features Ref.

No. Tri-iso-octyl amine (TIOA)

HCl< 4 M Carbon tetra-chloride

Rapid procedure. 10

Alamine 336 (A336)

HCl Kerosene Method was applicable for Ru(III) and Rh(III) also.

11

pH 2-3 - Method was applicable for other PGMs

12

HCl The percentage of Ir(III) increases with increasing HCl concentration of up to 8 M. Extraction was much higher

than TBP.

13, 14

Ir(III) separated from Rh(III).

14

Alamine 300 HCl _ Method was applicable for Ru(III) and Rh(III)

15

Aliquat 336 HCl - Method was applicable for Ru(III) and Rh(III)

15, 16

Stripping by aqueous ammonia.

Tertiary amines Cl2 / HCl - Iridium(III) separate from other platinum group metals (PGM) from Cl2/HCl leaching of the ores or concentrations converted into thiourea eluate resin were studied

16

N-n-octyaniline Sodium malonate

Xylene Method was applicable for the separation of iridium(III) from rhodium(III).

Iridium(III) was backstripped by 2 M HCl.

18

Tri-octylamine (TOA)

- Isoamyl alcohol

Carbonyl-chloride complexes of iridium extracted

19

4-(non-5-yl) pyridine

- Chloroform Method was applicable for Rh(III)

20

4-octylamino- pyridine

HCl, 1 M Chloroform The PGMs showed no mutual interference.

21

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

233

2-mercapto benzothiazole

- HCl, 7.1 M

Chloroform -

Analysis of real samples. 1.5 h heating Oxygen containing inert

solvent improved extraction. In benzene, carbon tetra-

chloride or hexane forms voluminous white precipitate at interface of aq./org. phase.

22-25

N,N'-Dipyridylthiou-rea

- Chloroform Method was applicable for Os(VI)

26

N,N-diethyl-N'-benzoylthiourea (DEBT)

HCl, 2.0 M

Toluene Selectivity in the order Pd(II)>Pt(II)>Ru(III)>Rh(III)>Ir(III) when ligand/metal ratio becomes >4.

27

N-benzoyl-NN’-dihexyl thiourea

pH, 3 Solvesso 150 Cu, Fe co-extract Heating at 950C

28

N-mono and N,N-di-substituierten benzoylthiourea

HCl, 2 M Toluene Separation of Ir from other platinum group metals. Extraction more efficient at

80oC

29

Thiobenzanilide Thiourea, 0.2 M HCl, 0.5 M

Chloroform butanol (7:1) Chloroform

Method used for the deter-mination of Ir in materials rich in Fe and non-ferrous metals. Rapid method for determi-

nation of noble metals at ppm level. KI and SnCl2 labilizing

agents

30, 31

1,3-Mono-thiodicarbonyl [1-carbonyl-3-thioxo] compounds

Acetate buffer pH = 5-7

- Heat at 80oC for 1 h. 92 % recovery of Ir

32

Potassium ethyl xanthate

- Chloroform

Method used for extraction of 30 elements

33

Dipropyl sulfide

- - Method also used for extraction of Pt, Rh and Ru

34

Dialkyl sulphoxide

HCl - Method was applicable for other PGMs

35

MITKhAT HCl - Extraction of iridium(III) and iridium(IV)

36

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

 

234 

Cyanex- 923 (C923)

HBr Toluene Iridium(III) separated from Pt(IV), Pd(II), and Rh(III)

Extraction of Ir(III) decreased with the increased concentration of stannous chloride.

Exothermic reactions

37

HCl and NaCl

n-octane, n-nonane, n-dodecane, kerosene, cyclohexane, toluene, and xylene

Third phase formation in the solvent extraction system Ir(IV)

38

HCl Toluene Recovery from spent autocatalysts

39

Cyanex 272, LIX 54, Cyanex 471, Cyanex 921, LiX-860N-I

HCl, HBr

Toluene Also applicable for other PGMs.

15, 37

Tri-butyl phosphate

HCl, 3.5-6 M

Toluene Monomeric anionic chloro complexes and polymeric aquachloro or aqua-oxo-complexes produced.

Rhodium(III) and Iridium(IV) separated from each other.

15, 40-41

Bis-(2-ethyl-hexyl) hydrogen phosphate (HDEHP)

HCl, 0.2 M pH=4.05 HCl, 0.5 M and thiourea 0.5 M pH,4.50

Isopar M 11.5 % Ir(III) extracted

28.5 % Ir(III) extracted. 95 % Back extraction into

1 M HCl

42, 43

Trioctyl phosphine oxide

- - Ir(III) purity of 99.99 % Separation of other PGMs

also studied. continuous solvent extraction

44

Triphenyl-phosphine

HCl 1,2-Dichlo- roethane

Stannous chloride used as labilizing agent. Useful for group concen-

tration before determination by AAS.

45

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

235

Triphenyl propylphos- phonium chloride

Ascorbic acid 0.5 %; HCl, 4 M

Chloroform Method applied for identification of Ir in alloys and ores.

46

n- propyl alcohol-sodium chloride

HCl - Separation of iridium from Pt(IV), Pd(II), Rh(III) and Au(III) Determination of iridium in

Pt-Pd-Ir alloy samples.

47

N,N,N-trioctyl aniliniumO,O-di(iso-propyl)dithio-phosphates

- - Method was applicable for platinum and rhodium.

48

Salicylhydro-xamic acid(SHA)

HCl Isobutanol Separation of iridium from rhodium and ruthenium

49

1,3,3-trimethyl-3H-indolium

pyruvic acid

- Method was applicable for rhodium.

50

α-n-nonylpyridine-N-oxide (NPO)

0.5-1 M HCl

- Effectively separates Pt(IV) and Ir(III) by extraction

51

N-hexyl isooctylamide

HCl - Effectively separates Ir(III) and Rh(III) by extraction

52

MIBK HCl

- Pre-equilibration with water to remove platinum. The method of standard

addition should be used

53

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

 

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7.3 Experimental

7.3.1 Instruments

An Elico digital spectrophotometer Model 12 Chemito 215D with 1 cm

quartz cells was used for absorbance measurements and pH adjustments were

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

operations were carried out by using Tapson’s analytical single pan balance

model 200 T having 0.001 g accuracy.

7.3.2 Chemicals and solutions

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

iridium trichloride hydrate (Johnson Matthey, UK) in dilute analar

hydrochloric acid (1 M) and diluting to 250 mL with water and standardized

gravimetrocally [54]. A working solution of 50 µg/mL was made from it by

diluting the stock solution with water.

n-Octylaniline

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

[55] and its 0.2 M solution was prepared in xylene. All other solutions were

prepared from A. R. grade reagents and aqueous solutions were prepared using

water. Double distilled water used throughout the experimental study.

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.

7.3.3 General extraction and determination procedure for iridium(III)

An aliquot of 50 μg iridium(III) solution was mixed with a sufficient

quantity of sodium malonate to make its concentration 0.06 M in a total

volume of 25 mL of the solution. The pH of the aqueous solution was adjusted

to 8.0 by dilute sodium hydroxide and hydrochloric acid solution. The solution

was then transferred to a 125 mL separating funnel and shaken with 10 mL of

0.2 M n-octylaniline in toluene for 3 min. After separating the two phases, the

aqueous phase was discarded and the organic phase was stripped with two

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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237

10 mL portions of 2 M hydrochloric acid solution. The stripped aqueous phase

was evaporated to moist dryness and extracted into water. The residue was

dissolved in minimum amount of 1 M hydrochloric acid and transferred into

25 mL volumetric flask and then 5 mL of concentrated hydrobromic acid was

added to it. The solution was mixed well and heated for 10 min in boiling water

bath, then to the same, 5 mL 25 % stannous chloride in concentrated

hydrobromic acid was added, mixed well and again heated for 2 min. The

cooled solution was diluted to 25 mL with water, and the absorbance was

measured at 400 nm against a blank solution. The concentration of iridium(III)

was computed from the calibration curve in similar manner [56].

7.4 Results and discussion

7.4.1 Extraction as a function of pH

The extraction studies of iridium(III) was performed at fixed

concentration of 0.06 M sodium malonate and between pH 1-10 with a 0.2 M

solution of n-octylaniline in toluene (Table 7.2). The pH range observed for the

quantitative extraction was 7.0-8.5 with n-octylaniline. Hence, the extraction of

iridium(III) were carried out at pH 8.0 for all extraction experiments (Fig. 7.1).

7.4.2 Effect of n-octylaniline concentration

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

n-octylaniline in toluene. 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 iridium(III) was quantitative in the range 0.12 M to 0.30 M

of n-octylaniline in toluene (Table 7.3). However, 10 mL of 0.2 M

n-octylaniline in toluene was recommended for general extraction procedure

(Fig. 7.2).

7.4.3 Effect of weak organic acid concentration

The extraction of iridium(III) was examined at pH 8.0 with 0.2 M

n-octylaniline in toluene in presence of varying concentrations from

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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238 

0.005 - 0.1 M of various weak organic acids (Table 7.4). The extraction of

ion-pair complex of iridium(III) was found to be quantitative in the range of

0.050 – 0.065 M sodium malonate. Hence, 0.06 M concentration of sodium

malonate was used for further studies while incomplete extraction of

iridium(III) was found to be in sodium salicylate and in sodium succinate

(Fig. 7.3).

7.4.4 Effect of diluents

The studies were then performed to find out the most suitable solvent for

the extraction of the ion-pair complex of iridium(III).It was found that a 0.2 M

solution of n-octylaniline in benzene, toluene, xylene, n-butyl alcohol, amyl

alcohol, amyl acetate provides quantitative extraction of iridium(III). The

extraction of iridium(III) was incomplete if n-octylaniline is dissolved in

chloroform (44.7 %) while no extraction was observed in methyl isobutyl

ketone, 1,2-dichloroethane (Table 7.5). On safety ground, toluene was

preferred to other solvents.

7.4.5 Effect of equilibration time

The extraction of iridium(III) was studied for various time intervals in

the range of 10 sec - 20 min with 0.2 M n-octylaniline (Table7.6). It was

observed that, under the optimized experimental conditions a minimum 1 min

time interval was required for attaining equilibrium in the sense to extract

iridium(III) quantitatively. But with prolonged shaking over 12 min there was

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

ion-pair complex. Hence, in all further studies the both phases were

equilibrated for 3 min. (Fig 7.4)

7.4.6 Effect of stripping agent

Iridium(III) from organic phase was stripped with the two 10 mL

portions of various stripping agents at different concentrations of mineral acids,

buffer solutions and some bases. Iridium(III) was quantitatively stripped with

hydrochloric acid (1.0 M to 5.0 M) (Table 7.7 ). However, percentage recovery

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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239

of iridium(III) from organic phase was found to be incomplete with strippants

as water, nitric acid (1.0 M to 3.0 M), sulphuric acid (1.0 M to 3.0 M) and

hydrobromic acid (1.0 M to 3.0 M) and there was no extraction in ammonia

buffer (pH 10), ammonia, sodium chloride. In recommended procedure, two

10 mL portions of 2.0 M hydrochloric acid were used for the complete

stripping of metal from loaded organic phase.

7.4.7 Effect of aqueous to organic volume ratio

The extraction of iridium(III) was carried out in different aqueous

volumes in the range 150-10 mL from 0.06 M sodium malonate medium with

10 mL 0.2 M n-octylaniline in toluene (Table 7.8). The quantitative extraction

of iridium(III) was observed when phase ratio, A/O, varied from 10:10 to

50:10. Therefore in the recommended procedure the phase ratio 2.5:1 was

maintained through the all experimental study.

7.4.8 Metal loading capacity of extractant

The influence of the initial iridium(III) concentration 25-3000 µg on the

extraction by 0.2 M n-octylaniline in toluene was studied. It was observed that,

varying the initial iridium(III) concentration in the range of 25-1300 µg has no

significant influence on iridium(III) extraction with the 10 mL of 0.2 M

extractant (Table 7.9). The maximum loading capacity of 10 mL 0.2 M solution

of n-octylaniline in toluene was found to be 1300 µg iridium(III).

7.4.9 Nature 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[Ir(III)] against

log C[n-octylaniline] at fixed sodium malonate concentration (0.06 M) were found to

be linear and having slopes of 1.2 and 1.3 values at pH 5.0 and 6.0, respectively

(Fig. 7.5). Also plots of log D[Ir(III)] against log C[malonate] at fixed

n-octylaniline concentration (0.2 M) were linear and slope values were found to

be 1.9 and 2.0 at pH 5.0 and 6.0, respectively (Fig. 7.6). The probable

composition of extracted species was calculated to be 1:2:1 (metal : acid :

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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

protonated n-octylaniline which forms cationic species as

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

iridium(III) to form anionic species as Ir(C3H2O4)-2(aq) and both of them unite

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

2]org which being

neutral constituted extractable species. CH3(CH2)7C6H4NH2(org)+ H+ CH3(CH2)7C6H4NH3

+(org) (7.1)

Ir3+(aq)

+ 2C3H2O4-(aq) Ir(C3H2O4)2

-(aq) (7.2)

CH3(CH2)7C6H4NH3+

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

+Ir(C3H2O4)2-](org)(7.3)

7.4.10 Effect of diverse ions

The effect of various cations and anions on recovery of iridium(III) was

investigated. The tolerance limit was set as the amount of foreign ion causing a

change ± 2 % error in the recovery of iridium(III). It was observed that the

method is free from interference from a large number of cations and anions.

Initially the foreign ion was added to the iridium(III) solution in large excess;

100 mg for anions and 15 mg for cations. When interference was found to be

intensive, the tests were repeated with successively smaller amount of foreign

ion. The only species showing interference of Rh(III) was eliminated by

masking with citrate. The anionic species showing interference in the

procedure were EDTA, thiocyanate, thiosulphate (Table 7.10).

7.5 Applications

7.5.1 Separation and determination of iridium(III) from binary mixture

The separation of Ir(III) from some commonly associated metal ions

like Pt(IV), Pd(II), Ru(III), Au(III), Os(VIII), Se(IV), Te(IV), Fe(III), Co(II),

Ni(II) and Cu(II) using n-octylaniline can be achieved by taking advantage of

the difference in the extraction conditions of metal such as pH of the aqueous

phase, reagent concentration and use of masking agent (Table 7.11).

Rh(III) interfere in the extraction of Ir(III). Rh(III) and Ir(III) were

separated from each other by masking Rh(III) with 10 mg citrate. Iridium(III)

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was separated from these associated metal ions, under the optimum extraction

conditions of Ir(III) where, all the added metal ions were remained

quantitatively in aqueous phase from which they are determined

spectrophotometrically by standard methods [56- 61].

7.5.2 Determination of iridium(III) in a synthetic mixture

Iridum(III) was determined from multicomponent mixture where

associated metal ions are present in it. A solution containing 50 µg of

iridium(III) was taken and known amounts of other metals were added. The

extraction of iridium(III) was carried out using the method developed. The

results obtained were in good agreement with the amounts taken (Table 7.12).

7.5.2 Separation of iridium(III) from ternary mixtures

The method was extended to the determination of iridium(III) in some

synthetic mixtures of associated metal ions. The iridium(III) was extracted

using the proposed method and the results are presented in Table 7.13. Rh(III)

interfere in the extraction of Ir(III). Rh(III) masked with 10 mg citrate at the

time of extraction.

7.6 Conclusion

Quantitative extraction of iridium(III) was achieved in 3 min with 0.2 M

n-octyaniline in xylene at pH 8.0.

Extraction reaction occurred through anion-exchange mechanism.

Developed method is efficient for quantitative separation of iridium(III)

in presence of various interfering cations and anions.

The proposed extractive separation method is simple, rapid, selective

reproducible and suitable for separation and determination of

iridium(III) from associated metal ions and synthetic mixtures.

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Table 7.2 Extraction of iridium(III) as a function of pH

Ir(III) = 50 μg Aq: Org = 2.5: 1

Sodium malonate = 0.06 M n-Octylaniline = 0.2 M in toluene

Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid

(2×10 mL)

pH Percentage extraction,

(% E) Distribution ratio,

(D)

1.0 - -

2.0 - -

3.0 - -

4.0 29.8 1.06

5.0 47.9 2.29

6.0 66.2 4.89

6.2 72.3 6.52

6.4 83.0 12.20

6.6 88.1 18.50

6.8 93.9 38.15

7.0 100 ∞

7.5 100 ∞

8.0* 100 ∞

8.5 100 ∞

8.8 91.5 26.91

9.0 85.9 15.23

10.0 60.0 3.75

* Recommended for general extraction procedure

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Table 7.3 Extraction behaviour of iridium(III) as a function of

n-octylaniline concentration

Ir(III) = 50 μg Aq: Org = 2.5: 1

Sodium malonate = 0.06 M pH = 8.0

Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid

* Recommended for general extraction procedure

n-Octylaniline, (M)

Percentage extraction, (% E)

Distribution ratio, (D)

0.01 - -

0.02 - -

0.03 - -

0.04 45.9 2.12

0.05 58.9 3.58

0.06 68.9 5.53

0.07 73.8 7.04

0.08 79.9 9.93

0.09 85.9 15.23

0.10 89.9 22.25

0.11 93.9 38.48

0.12 100 ∞

0.14 100 ∞

0.16 100 ∞

0.18 100 ∞

0.20* 100 ∞

0.22 100 ∞

0.24 100 ∞

0.28 100 ∞

0.30 100 ∞

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Table 7.4 Extraction behavior of iridium(III)as a function of weak

organic acid concentration

Ir(III) = 50 μg Aq: Org = 2.5: 1

n-Octylaniline = 0.2 M in toluene pH = 8.0

Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid (2×10 mL)

Acid concentration

(M)

Sodium malonate Sodium salicylate Sodium succinate

% Ea Db % E Db % E Db

0.005 30.3 1.08 14.9 0.43 18.9 0.58

0.010 37.9 1.52 20.9 0.66 22.0 0.70

0.020 77.6 8.66 47.9 2.29 25.8 0.86

0.030 84.5 13.62 58.9 3.58 30.3 1.08

0.040 87.5 17.5 61.8 4.04 37.0 1.46

0.050 100 ∞ 48.8 2.38 46.9 2.20

0.055 100 ∞ 35.2 1.35 55.3 3.09

0.060* 100 ∞ 27.9 0.96 68.3 5.38

0.065 100 ∞ 20.0 0.62 51.3 2.63

0.070 98.2 137.38 11.0 0.30 50.0 2.5

0.080 89.9 22.25 10.3 0.28 38.8 1.58

0.090 85.2 14.39 - - 19.8 0.61

0.10 62.0 4.07 - - 12.9 0.37 * Recommended for general extraction procedure a = Percentage extraction b= Distribution ratio

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Table 7.5 Extraction behaviour of iridium(III) as a function of

diluents

Ir(III) = 50 μg Aq: Org = 2.5: 1

n-Octylaniline = 0.2 M pH = 8.0

Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid

Sodium malonate = 0.06 M (2 × 10 mL)

Solvent Dielectric

constant, (ε)

Percentage extraction,

(% E)

Distribution ratio, (D)

Benzene 2.27 100 ∞

Xylene 2.30 100 ∞

Toluene* 2.38 100 ∞

Chloroform 4.80 44.7 2.02

Methyl isobutyl ketone

13.10 No extraction -

n-Butyl alcohol 17.80 100 ∞

Amyl alcohol 13.90 100 ∞

Amyl aceate 13.90 100 ∞

1, 2-Dichloroethane 10.50 No extraction -

* Recommended for general extraction procedure

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Table 7.6 Extraction behavior of iridium(III) as a function of

equilibrium time

Ir(III) = 50 μg Aq: Org = 2.5: 1

n-Octylaniline = 0.2 M toluene pH = 8.0

Strippant = 2 M Hydrochloric acid Sodium malonate = 0.06 M

(2×10 mL)

Time in min Percentage extraction,

(% E )

Distribution ratio,

( D )

10 sec 32.3 1.19

15 sec 43.7 1.94

30 sec 74.5 7.30

1 100 ∞

2 100 ∞

3* 100 ∞

4 100 ∞

5 100 ∞

6 100 ∞

7 100 ∞

8 100 ∞

9 100 ∞

10 100 ∞

12 100 ∞

14 93.9 38.48

16 89.2 20.64

18 58.8 3.56

20 41.9 1.80

* Recommended for general extraction procedure

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Table 7.7 Extraction behavior of iridium(III) as a function of

stripping agents

Ir(III) = 50 μg Aq: Org = 2.5: 1

n-Octylaniline = 0.2 M toluene pH = 8.0

Sodium malonate = 0.06 M

Strippant M / pH Percentage extraction,

(%E )

Ammonia

1-10

No stripping

HCl*

1-5

100

H2SO4

1-3

47.3

HNO3

1-3

46.9

HBr

1-3

89.9

Water

-

10.2

NaCl

1-5 %

No stripping

Ammonia buffer pH-10 No stripping

* Recommended for general extraction procedure

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Table 7.8 Extraction of iridium(III) as a function of aqueous to organic

volume ratio

Ir(III) = 50 μg

n-Octylaniline = 0.2 M toluene pH = 8.0

Strippant = 2 M Hydrochloric acid Sodium malonate = 0.06 M

(2 × 10 mL)

* Recommended for general extraction procedure

Aqueous to organic volume ratio

Percentage extraction,

( % E )

Distribution ratio, ( D )

10:10 100 ∞

20:10 100 ∞

25:10* 100 ∞

30:10 100 ∞

35:10 100 ∞

40:10 100 ∞

50:10 100 ∞

70:10 93.7 37.18

100:10 61.3 3.95

150:10 36.1 1.41

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Table 7.9 Metal loading capacity of n-octylaniline

Ir(III) = 50 μg Aq: Org = 2.5: 1

n-Octylaniline = 0.2 M toluene pH = 8.0

Strippant = 2 M Hydrochloric acid Sodium malonate = 0.06 M

(2×10 mL)

Ir(III), ( μg ) Percentage extraction,

( % E )

Distribution ratio,

( D)

25 100 ∞

50* 100 ∞

100 100 ∞

200 100 ∞

300 100 ∞

400 100 ∞

600 100 ∞

800 100 ∞

1000 100 ∞

1200 100 ∞

1300 100 ∞

2000 87.9 18.16

2500 70.9 6.09

3000 44.8 2.02

* Recommended for general extraction procedure

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Table 7.10 Effect of foreign ions on the extraction of 50 μg iridium(III)

at pH 8.0 in 0.06 M sodium malonate with 0.2 M n-octyaniline

in toluene

a = Masked with 10 mg citrate.

Ratio of ions

Iridium: ion

Mass tolerated /

mg Foreign ion

2:150

15

Bi(III), Nitrate , fluoride

2:100

.

10

V(V), Mn(II), Mg(II), Ni(II), Co(II), Pb(II), Cu(II), Zn(II), Se (IV), Cd(II), Sn(II), Tl(III), citrate, ascorbate, thiourea, Cr(III), Ti(IV).

2:50

5

Ti(IV), Cr(VI), Fe(III), Sb(III), U(VI), W(VI), Mo(VI), Te(IV), Hg (II).

2:20

2

Au(III), Ag (I)

2:1

1

Ru(III), Os(VIII)

2:0.5

0.5

Rh(III) a Pt(IV), Pd(II)

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Table 7.11 Separation of iridium(III) from binary mixtures

*average of five determinations. a = masked by 10 mg by citrate.

Amount of metal ion,

(μg)

Mass taken/µg

Average (%) recovery*

Chromogenic ligand

Ref. No.

Ir(III) Rh(III)a

50 100

99.0 97.4

stannous chloride-hydrobromic acid

[56]

Ir(III) Ru(III)

50 200

99.9 98.9

4’-ChloroPTPT

[57]

Ir(III) Pt(IV)

50 300

99.0 99.4

stannous chloride-hydrochloric acid

[56]

Ir(III) Pd(II)

50 200

98.8 98.4

4’-ChloroPTPT

[57]

Ir(III) Au(III)

50 200

98.8 97.1

SnCl2

[56]

Ir(III) Se(IV)

50 200

99.0 97.0

4’-BromoPTPT

[59]

Ir(III) Te(IV)

50 200

98.8 98.9

4’-BromoPTPT

[60]

Ir(III) Os(VIII)

50 200

98.0 99.3

Thiourea

[56]

Ir(III) Fe(III)

50 500

99.0 98.8

Thiocynate

[56]

Ir(III) Cu(II)

50 1000

99.0 98.7

4’-ChloroPTPT

[61]

Ir(III) Ni(II)

50 1000

99.0 98.9

DMG

[58]

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Table 7.12 Analysis of synthetic mixture for iridium(III) content from

associated elements

Composition, µg Ir(III) found

µg Recovery* % RSD %

Ir(III), 50; Pd(II),100; Pt(IV),100.

49.8

99.6

0.4

Ir(III),50; Pt(IV),100; Os(VIII),100.

49.9

99.8

0.2

Ir(III),50; Pt(IV),100; Ru(III),100.

49.8

99.6

0.4

Ir(III),50; Pd(II),100; Pt(IV),100;Rh(III)a,100; Ru(III),100.

49.7

99.4

0.6

Ir(III),50, Cu(II),1000; Ag(I),100;Au(III),100.

49.7

99.4

0.6

Ir(III),50; Pd(II),100;

Pt(IV),100;Rh(III)a,100;

Ru(III),100;Os(VIII).

49.8

99.6

0.4

a masked with 10 mg citrate *average of five determinations.

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Table 7.13 Separation of iridium(III) from ternary mixtures

Metal ion

Amount taken,

μg

Ir(III) found

µg

Average recovery of iridium(III),*

% Ir(III)

Rh(III)a Pt(IV)

50 200 100

49.7 99.4

Ir(III)

Rh(III)a Pd(II)

50 200 200

49.7 99.4

Ir(III)

Cu(II) Ni(II)

50 200 100

49.4 98.9

Ir(III)

Pd(II) Cu(II)

50 200 200

49.5 99.0

Ir(III)

Pt(II) Au(III)

50 100 100

49.5 99.0

* Average of five determinations a masked with 10 mg citrate

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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. 7.1 Plot of pH versus percentage extraction of iridium(III)

(50 μg/mL) from malonate medium (0.06 M) by using

n-octylaniline (0.2 M) as an extractant in toluene with 3 min

shaking time.

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0

10

20

30

40

50

60

70

80

90

100

0 0.05 0.1 0.15 0.2 0.25 0.3

n-octylaniline (M)

Perc

enta

ge E

xtra

ctio

n (%

E)

Fig. 7.2 Extraction of iridium(III) (50 µg/mL) at pH 8.0 from

0.06 M sodium malonate as a function of n-octylaniline

concentration.

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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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

Weak Acid (M)

Perc

enta

ge E

xtra

ctio

n (%

E)

Sodium malonateSodium salicylateSodium succinate

Fig. 7.3 Extraction of iridium(III) (50 µg) with 0.2 M n-octylaniline at

pH 8.0 as a function of weak acid concentration.

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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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 11 12 13 14 15 16 17 18 19 20Time in Min.

Perc

enta

ge E

xtra

ctio

n (%

E)

Fig. 7.4 Extraction of iridium(III) (50 µg/mL) at pH 8.0 from

0.06 M sodium malonate as a function of equilibration

period.

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■ Slope = 1.2 at pH 5

▲ Slope= 1.3 at pH 6.0

-0.1

0

0.1

0.2

0.3

0.4

-1.4 -1.3 -1.2 -1.1 -1 -0.9

Log C [n-octylaniline]

Log

D[I

r(II

I)]

Fig. 7.5 Log-log plot of distribution ratio D[Ir(III)] versus Log C[n-octylaniline]

at fixed malonate concentration.

Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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■ Slope = 1.9 at pH 5 ▲ S lope= 2.0 at pH 6

-0.9

-0.7

-0.5

-0.3

-0.1

0.1

0.3

0.5

0.7

0.9

-2.1 -1.9 -1.7 -1.5 -1.3 -1.1

Log C [malonate]

log

D[I

r(II

I)]

Fig. 7.6 Log-log plot of distribution ratio D[Ir(III)] versus Log C[malonate]

at fixed n-octylaniline concentration.

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Chapter 7  Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger  

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261

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