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Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 68
CHAPTER-4
SOLVENT EXTRACTION STUDIES OF RHODIUM(III) USING HIGH MOLECULAR WEIGHT AMINE
4.1 Introduction
At present there is growing demand of platinum group metals, the name
platinum group metals (PGMs) include the six elements: ruthenium, rhodium,
platinum, palladium, osmium and iridium. In the past few decades these metals
have found new applications outside the jewellery and decorative industries
due to its excellent physical and chemical properties and are used extensively
for electronic devices, catalysis in the chemical and petroleum refining
industries, glass industries, pharmaceutical industries etc. Rhodium is one of
the most expensive platinum group metal and is indispensable for automotive
catalytic converters.
The high cost of recovery and limited resources of these metals make it
necessary to recover the metals from industrial waste. Considering the
difficulties related with the separation and purification of PGMs, it is important
to find an effective separation process to recover these metals with high purity
[1]. According to the published literatures, ion exchange and solvent extraction
have been widely employed to separate and recover them. Among Pt, Pd and
Rh, extraction of Rh is the most difficult owing to its intricate chemical
properties in chloride solution. Rhodium has seven existence forms of aqua-
chloro complexes from [Rh(H2O)6]3+ to [RhCl6]3-. The highly charged
octahedral complexes are difficult to extract owing to steric effects [2].
The extent to which a metal ion is extracted from an aqueous into an
organic phase is the result of many factors. One of these factors is the amount
of water which accompanies the metal complex. This water favors the
solubility of the metal complex in the aqueous phase and disfavors its solubility
in the organic phase. In the case where the metal ion is fully co-ordinated, i. e.,
all its co-ordination sites are occupied by ligand donor atoms, the water will
form the outer sphere of the complex by means of solvation (hydration).
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 69
Though, several sophisticated techniques are in use for the
determination of trace and ultra trace quantities of rhodium, spectrometric
technique still has the advantage in respect to simplicity and low operating
costs but suffers due to matrix effects. Hence, separation and preconcentration
of trace level quantities of rhodium is necessary prior to actual quantitative
analysis. Several extraction procedures are available for this purpose however
most of these are time consuming and costly, however liquid-liquid extraction
technique is one of the most suitable, selective, efficient and powerful
technique for the separation and purification of platinum group metals [3].
4.2 Review of literature for liquid-liquid extractive separation of
rhodium(III)
A variety of high molecular weight amine (HMWA) have been
explained extraction of rhodium(III) like almine 336 (A336) [4-7]. In order to
find an optimum condition to separate rhodium and iridium, solvent extraction
experiments were performed from chloride solution by using alamine 336 and
tri-n-butyl phosphate (TBP) as an extractant. The extraction depends on
concentration of hydrochloric acid [7]. Tri-octylamine [8-11], tri-iso-
octylamine (almine 308) [12], aliquat 336 [13, 14], N-n-octylaniline [15],
tetraoctyl and trialkylbenzylammonium chlorides [16], trioctyl-methyl-
ammonium chloride (TOMAC) [17,18], 4-(non-5-yl) pyridine [19],
4-octylamino pyridine [20], 2-ethylhexyl amino methyl pyridine [21] have been
tested for liquid-liquid extraction of rhodium(III).
Phosphorous containing extractant such as tri-n-butyl phosphate [22] has
been used for the quantitative extraction and separation of trace amounts of
rhodium from nitric acid and sodium trichloroacetate media has been
established based on the formation of an ion-association complex of
hexahydrated rhodium cation Rh(H2O)6 3+ and the trichloroacetate (TCA) anion
in tri-n-butyl phosphate (TBP). A systematic study on the solvent extraction of
rhodium with TBP in hydrochloric acid in presence of stannous chloride [23,
24] has been reported. Liquid-liquid extraction of rhodium(III) with
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 70
cyanex 921 from aqueous hydrochloric acid media [25], hydrobromic acid [26]
and chloride media [27] has been examined in the presence and in the absence
of stannous chloride. The extraction of rhodium(III) from bromide media [28]
with cyanex 923 and cyanex 471-X in toluene was studied. The extraction of
rhodium(III) from its chloride solution was carried out using cyanex 923,
cyanex 271 and cyanex 272 [27, 29-30] and distribution ratios for the metals
were determined under the different concentrations of H+ Cl- ions in the
aqueous phase. Separation of rhodium(III) from aqueous solution with tri-n-
octylphosphine oxide (TOPO) [31] was studied by using stannous chloride as
activating reagent. The formation of complex required 60oC temperature.
Percentage of stripping could reach 95 % only. Hexaaquarhodium(III),
(Rh(H2O)63+) was found to be extracted quantitatively within 5 min by shaking
with trichloroacetic acid (HTCA) and TOPO [32] in heptane with a pH range
of 3-5. The chemical species extracted is Rh3+.3TCA-.4TOPO and the
extaction constant (log K) for the equilibrium is 12.29 ± 0.06. Solvent
extraction behavior of hexaaqua Rh(III) was investigated in systems containing
picric acid and trioctylphosphine oxide (TOPO) [33] in heptane, benzene,
chloroform, 1,2-dichloroethane and nitrobenzene. The presence of picric acid
and TOPO was found to be effective in rapid extraction of Rh(III) at room
temprature. Solvent extraction of rhodium with bis-(2-ethyl) hexylphosphoric
acid HDEHP [34, 35] from thiourea chloride media was investigated. Under
optimum condition, rhodium(III) was extracted up to 88.3 %. Solvent
extraction of rhodium(III) from acidic media with D2EHPA [36] in toluene
was carried out after optimizing the conditions of extraction. The organic phase
containing extracted rhodium(III) was strriped with 4 M HCl.
Aneva et. al. investigated a scheme described for determination of noble
metals, combines solvent extraction procedures with atomic absorption
spectrometric [37] and graphite furnace atomic absorption spectrometric [38]
determination of rhodium in high-purity platinum matrix or material. The
metal ion was extracted into isoamyl alcohol-isobutyl methyl ketone (MIBK)
[39]. Extraction of rhodium(III) from hydrochloric acid solutions with dihexyl
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 71
sulfoxide (DHSO) [40] and with petroleum sulfoxides (PSOs) [40, 41] was
studied, and the optimal conditions for its recovery were found. Method
required 30 min phase contact time for extraction of rhodium(III) with
sulfoxides. Rhodium was extracted from an Rh-Sn-Cl system, with dialkyl
sulfoxide (DEHSO) [42] as the extractant and with stannous chloride as the
activator. The results indicate that the extraction rate of rhodium increases
with the molar ratio of Sn to Rh till the maximum of 99 % at a molar ratio of
6:1.
In comparison to these nitrogen-sulphur containing reagents, Schiff
bases showed promising effects in the field of analytical chemistry for the
separation and estimation of platinum group metals [43]. Rhodium being a soft
acid, can be selectively extracted with soft donor base extractants containing
‘N’ or ‘S’ atoms. Based upon this several extractants, namely, 4-(4-
ethoxybenzylideneamino)-5- methyl-4H-1, 2, 4-triazole-3-thiol (EBIMTT)[44],
N-mono-and N,N- di-substituted benzoylthiourea [43], N,N-di-n-hexyl-N'-
benzoylthiourea [45], N,N-Dialkyl-N′-benzoylthiourea [46], 4-(4-
methoxybenzylideneamino)-5-methyl-4H-1,2,4-triazole-3-thiol [47], Dibutyl,
dioctyl or dibenzyl sulphide [Thioethers (sulphides)] [48, 49] have been studied
or used for extraction of rhodium(III).
A method is proposed for the extraction and simultaneous
spectrophotometric determination of Rh(III) with benzil α-monoxime [50]. In
hot condition, Rh gives a yellow chelate at pH 1-6 with the reagent, which is
extractable into chloroform. The absorbance was measured at 400 nm. The
recovery and purification of rhodium from spent [51] castable refractory of
glass fiber industry are discussed. The rhodium was well extracted by a series
of treatments including aqua regia dissolution, ion exchange, solvent
extraction and levextrel resin separation. The results show that the recovery
rates of rhodium can be above 90 %.
N,N'-dimethyl-N,N'-diphenyltetradecylmalonamide (DMDPHTDMA)
[52] in 1,2-dichloroethane has been investigated as a solvent extraction reagent
to mainly perform the separation of rhodium from other PGMs and from some
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 72
commonly associated elements contained in concentrated hydrochloric acid
media. The developed separation scheme was applied to an automobile
catalytic converter leaching solution. The pH effect was studied on solvent
extraction of rhodium sulfates with N-octyl-, N,N-dioctyl aniline and N,N,N-
trioctyl anilinium O,O-di(iso-propyl)dithiophosphates [53]. Correlation
between pH values and partition coefficient were discussed. Solvent extraction
of rhodium was carried out from chloride media with Kelex 100 [54, 55] in the
absence and presence of a large amount of tin. Stripping of metal ion from the
loaded organic phase increases with increasing concentration of oxidizing
agent. A separation procedure for platinum-group metal from lead matrix were
presented after fire-assay preconcntration. The procedure included thermal
dissociation of platinum-group metal nitrates and subsequent extraction with
toluene solution contaning alkylaniline hydrochloride and petroleum sulphide
[56, 57]. Rhodium(III) solution react with stannous chloride to form a short-
lived yellow complex which is extracted by polyurethane foam [58]. Method
was applicable for separation of iridium(III) on the basis of stability of
complex. Rhodium(III) can be extracted from iodide solution of
2-aminobenzothiazole (ABT) [59] into hexane at pH 1.0-3.0 after heating in
boiling-water bath for 60 min for the formation of the extractable complex.
Separation of rhodium from iridium was possible by this method.
Rhodium(III) and iridium(III) were separated satisfactorily in Tween 80-
(NH4)2SO4-H2O [60] system by the liquid-solid extraction as complexes with
stannous chloride. The use of commercially available solid phase extraction
(SPE) anion exchange cartridges [61] for the separation and preconcentration
of rhodium(III) in chloride aqueous samples was described and characterized.
The method was based on adsorption and preconcentration phenomenon.
A liquid emulsion membrane (LEM) system [62] as a tool for process
intensification has been studied for rhodium recovery using di-2-
ethylhexylphosphoric acid (D2EHPA) as a metal carrier and Monemul 80 as a
surfactant, dissolved in liquid paraffin. The extraction and structural properties
of rhodium complexes with stannous chloride using N,N-dioctyl hexanamide
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 73
(DOHA) [63] were investigated by solvent extraction and Rh k-edge X-ray
absorption fine structure from a 1 M HCl solution. However, the Rhodium
extraction was enhanced with an increase in the Sn(II) concentration in the
initial aqueous phase. The various investigated systems are presented in tabular
form in Table 4.1 to review the literature in terms of various extractants used
and special characteristics regarding those systems.
Development of new extraction system for extraction of rhodium(III)
especially in weak organic acid solutions is a topic of great interest.
n-Octylaniline with an exploring extracting capacity in malonate media belongs
to a kind of high molecular weight amine. Its potential advantages are as lower
cost, good physico-chemical properties, completely miscible with all common
hydrocarbon diluents, low aqueous solubility, good resistance to hydrolysis,
and high purity.
The present study represents experimental data on extraction of
rhodium(III) from malonate solutions and accesses n-octylaniline as an
extractant. The mechanism of extraction and nature of extracted complex was
sought. The key observation is that it is possible to separate rhodium(III)
directly from other associated rare earth and transition elements.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 74
Table 4.1 Summary of methods for solvent extraction of rhodium(III)
System Aqueous phase
Organic phase Special features Ref.
No. Alamine 336 HCl Kerosene Method was able to
eliminate the base metal ions commonly associated with Rh.
Method applicable for extraction of Pt(IV) and Ir(III) group metals.
4
HCl
1-5 M
Adding SnCl2 to the mixed solutions increased the extraction percentage of Rh.
Rh(III) separates from Pt(IV), Pd(II).
5
HCl
The percentage of Rh(III) increases with increasing HCl concentration of up to 8 M.
Extraction was much higher than TBP.
6,7
HCl Rh(III) separated from Ir(III).
7
Tri-octylamine
(TOA)
1 M HCl Toluene Rh(III) separated from Pt(IV), Pd(II).
8
Rh(III) separated from Pt(IV).
9
Isoamyl
alcohol
Carbonyl-chloride complexes of rhodium extracted
10
HCl Toluene 87.6 % of Rh(III) recoverd from catalytic converters.
HCl and HNO3 used in stripping study.
11
Tri-iso-
octylamine
(Alamine 308)
HCl Kerosene The percentage extraction of rhodium(III) increased with increase in acid concentration up to 8 M.
12
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 75
Aliquat 336 SCN- Dodecane Quaternary amines were the most effective for metal transport. Alipatic organic diluents
were chosen to avoid the degradation of the polymeric support. 1-dodecanol was used as
a modifier to increase solubility of extractant. Back extraction by 1M
NaHSO3
13
HCl Kerosene Extraction of rhodium(III) carried out with organo- phosphorus which is used as synergists extractants.
Method is also applicable for Pt(IV)
14
N-n-octylaniline Sodium malonate
Xylene Method is also applicable for separation of rhodium(III) from other associated metals specially from Ir(III)
15
Tetraoctyl and Trialkylbenzyl- ammonium chlorides
HCl - Depolymerisation rate constants are determined.
16
Trioctyl-methyl-ammonium chloride (TOMAC)
HCl Nitro-benzene or benzene
Extraction efficiency promoted in chlorobenzene, nitrobenzene and 1,2-dichloroethane and suppressed in CCl4 and CHCl3. Separation factor about 16
times greater than that from the solution containing oligomer and chloro species. Distribution ratio
increases with increase in temperature.
17, 18
4-(non-5-yl)
pyridine
HCl Chloroform Extraction increased with increase in concentration of reagent and chloride. 95 % rhodium extracted in
30 min. Rhodium and iridium could not be separated.
19
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 76
4-octylamino
pyridine
HCl, 0.5-1 M
Chloroform Fe, Co, Ni did not interfere Platinum group metals
showed no mutual interference.
20
2-ethylhexyl
amino methyl
pyridine
(EHAP)
HCl - Excellent selectivity over base metals. Highly slective
extractant for Rh(III), Pd(II) and Pt(IV) Equilibration time 5 h.
21
Tri-n-butyl
phosphate
HNO3 and
trichloro-
acetate
- Method applied for determination of rhodium traces in chloroplatinic acid and palladium chloride.
22
- - SnCl2 added four times that of rhodium. 100 % stripping by 4 M
HCl. 60oC, aging for 2 h.
23
solution of HCl and NaClO3
- Rhodium(III) and Iridium(IV) separated from each other from low quantities.
24
Cyanex 921 HCl;
HBr
Toluene Method is also applicable for extraction and separate ion of Pt(IV) and Pd(II).
Rhodium(III) has been examined in the presence and in the absence of stannous chloride
25,
26
Chloride solution
- Also useful for extraction of Ir(III)
27
Cyanex 923 and Cyanex 471-X
bromide media
Toluene Method is useful for extraction and separation from other platinum metals.
Stoichiometric ratio of Rh(III) with both extractants was 1:1.
28
Cyanex 923, Cyanex 471, Cyanex 472
HCl Toluene Recovery from spent autocatalysts.
29
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 77
Chloride
solution Kerosene Distribution ratios for the
metals were determined under the different concentrations of H+ Cl- ions in the aqueous phase.
30
Tri-n-
octylphosphine
oxide (TOPO)
stannous
chloride
- Stannous chloride used as activating reagent and it was four times that of Rh(III).
Complex formation required 60oC temperature.
Percentage extraction was 98 % and percentage of stripping could reach 95 %.
31
Trioctylphos-phine oxide (TOPO)
pH, 3-5 Trichloroacetic acid (HTCA)
Heptane Equilibration time 5 min. 32
Picric acid
Heptane/ benzene/ chloro-form/1,2-dichloro ethane/ nitro-benzene
The presence of picric acid & TOPO found effective in rapid extraction of Rh(III) at room temperature
33
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 90.7 % rhodium extracted. 88.3 % rhodium extracted More than 95 % back
extraction into 1 M HCl
34, 35
Toluene Back extaction into 4 M HCl Separation from some
noble metals.
36
MIBK HCl, HCl, 2-3 M, pH
Heating for 10-60 min
Method successfully applied to a converter matte. More than 95 % extraction.
37-
39
HCl, 6 M Cu-coextracts
Pre-equilibration with water to remove platinum. The method of standard
addition is used. Lower limit of
determination of rhodium 1 μg/g.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 78
Dihexyl sulfoxide (DHSO) and Petroleum sulfoxides (PSOs)
HCl - Method required 30 min phase contact time for extraction of rhodium(III)
Species were detected by IR spectra.
40, 41
Dialkyl sulphoxide
HCl - Stannous chloride used as activating reagent.
The results indicate that the extraction rate of rhodium increases with the molar ratio of Sn to Rh till the maximum of 99 %.
42
N’N’-dihexyl and phenyl and N’-hexyl and phenyl derivatives of N-benzoyl thiourea
HCl, 1mM – 6 M
Toluene The dihexyl derivative showed the highest extracting power. Increase in ligand
concentration improves the extent of extraction. Heat is required at
25o C to 80oC
43
4-(4-ethoxybenzylideneamino)-5- methyl-4H-1, 2, 4-triazole-3-thiol (EBIMTT)
Sodium malonate medium
Chloroform Method is applicable for the analysis of binary mixtures, synthetic mixtures, alloys and real samples.
44
NN-dihexyl-N’-benzoyl-thiourea
- - Extraction of rhodium(III) was accelerated in the presence of stannous chloride with metal-ligand ratio 1:9
45
N-benzoyl-NN’-dihexyl thiourea
pH,3 Solvesso 150 Separation of Rh, Ru, Pd, Os, Ir, Pt, Cu, Fe from Mn, Co and Zn. Heat at 950C, Cu, Fe and
Ni interfere.
46
4-(4-methoxybenzy- lideneamino)-5-methyl-4H-1,2,4-triazole- 3-thiol in hydrochloric acid
HCl Chloroform Extraction of microgram level concentration of rhodium(III)
Rhodium(III) was stripped from organic phase with 1 M hydrochloric acid
47
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 79
Dibutyl, dioctyl or dibenzyl sulphide [Thioethers (sulphides)]
HNO3 Hexanol The extent of extraction of Rh(NO2)6
3- is much greater than that of Rh(H2O)6
3+ Separation of rhodium
from Pd, Ru and Tc
48, 49
Benzil α-monoxime
pH 1-6 Chloroform In hot condition, Rh gives a yellow chelate The absorbance was
measured at 400 nm. The results show that the
recovery rates of rhodium can be above 90 %.
50, 51
N,N'-dimethyl-N,N'-diphenyltetrade-cylmalonamide (DMDPHTDMA)
HCl 1,2-Dichloroetha-ne
Method was applicable for separation of rhodium from other PGMs
52
N,N,N-trioctyl anilinium O,O-di(iso-propyl) dithiopho-sphates
- - Method was applicable for platinum and Iridium.
53
Kelex 100 HCl - Addition of large amount of tin in the feed solution increases the Rh extraction and decreases the Pd and Pt extraction. Selective separation of
rhodium Stripping increases with
increase in concentration of oxidising agent.
54
Rh-chloro complexes suppresses the liquid-liquid extraction of rhodium.
55
Alkylaniline hydrochloride petroleum sulphide
HCl, 6 M Toluene
Determination by flame or electrothermal AAS. Shaking for 30 min.
56, 57
Polyurethane foam
- - Rhodium(III) react with SnCl2 to form short lived yellow complex which was extracted by extractant.
58
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 80
2-aminobenzothi-azole
HCl, 0.2 M KI, 5 %; sodium acetate 10 %; pH=2 Chloro- acetic acid
Hexane Separation of rhodium from iridium. Heating for 60 min.
69
Tween 80-(NH4)2SO4-H2O
Stannous chloride
- Separation of rhodium from iridium possible by this method.
60
Solid-Phase Extraction Cartridges (SPE)
- - Separation and preconcentration of rhodium(III) in chloride aqueous samples was described and characterized. The method was based on
adsorption and preconcentration phenomenon.
61
Di-2- ethylhexyl phosphoric acid (D2EHPA)
HCl Paraffin Perchloric acid was found to be a better stripping agent .
62
N,N-dioctyl hexanamide (DOHA)[
- - Rh(III) extraction was enhanced with an increase in the Sn(II) concentration
63
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 81
4.3 Experimental
4.3.1 Instruments
An Elico digital spectrophotometer model 12 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 carried out by using Tapson’s analytical single pan balance
model 200T having 0.001 g accuracy.
4.3.2 Chemicals and solutions
Standard rhodium(III) solution
A stock solution of rhodium(III) was prepared by dissolving 1 g of
rhodium trichoride hydrate (Johnson Matthey, UK) in dilute analar
hydrochloric acid (1M) and diluting to 25 mL with water and standardised
gravimetrically [64]. A working solution of 100 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
[65] and its 0.1 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 was 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.
4.3.3 General extraction and determination procedure for rhodium(III)
An aliquot of 200 μg rhodium(III) solution was mixed with a sufficient
quantity of sodium malonate to make its concentration 0.03 M in a total volume
of 25 mL of the solution. The pH of the aqueous solution was adjusted to 9.0
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 0.1 M
n-octylaniline in xylene for 3 min. After separating the two phases, the aqueous
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 82
phase was discarded and the organic phase was stripped with two 10 mL
portions of 1 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
50 mL volumetric flask, 10 mL of 20 % potassium iodide was added, the
solution was mixed well, and heated for 15 min in boiling water bath. To the
cooled solution, 10 mL of 10 % stannous chloride solution was added and
diluted the solution upto the mark with water containing 1 M hydrochloric acid
in final concentration. The unstoppred flask was kept in the boiling water bath
for development of reddish brown solution which was measured at 445 nm
against a reagent blank. The concentration of rhodium(III) was computed from
the calibration curve in similar manner [66].
4.4 Results and discussion
4.4.1 Extraction as a function of pH
The extraction studies of rhodium(III) was performed at fixed
concentration of 0.03 M sodium malonate and between pH 1-10 with a 0.01 M
solution of n-octylaniline in xylene (Table 4.2). The pH range observed for the
quantitative extraction was 7.5-9.5 with n-octylaniline. Hence, the extractions
of rhodium(III) were carried out at pH 9.0 for all extraction experiments
(Fig. 4.1).
4.4.2 Effect of n-octylaniline concentration
Extraction of rhodium(III) was carried out with various concentrations
of n-octylaniline in xylene (Table 4.3). 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 rhodium(III) was quantitative in the range
0.07 M to 0.15 M of n-octylaniline in xylene. However, 10 mL of 0.1 M
n-octylaniline in xylene was recommended for general extraction procedure
(Fig. 4.2).
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 83
4.4.3 Effect of weak organic acid concentration
The extraction of rhodium(III) was examined at pH 9.0 with 0.1 M
n-octylaniline in xylene in presence of varying concentrations from
0.001 - 0.1 M of various weak organic acids (Table 4.4). The extraction of
ion-pair complex of rhodium(III) was found to be quantitative in the range of
0.025 – 0.035 M sodium malonate. Hence, 0.03 M concentration of sodium
malonate was used for further studies while incomplete extraction of
rhodium(III) was found to be in sodium salicylate and no extraction from
sodium succinate (Fig. 4.3).
4.4.4. Effect of diluents
The studies were then performed to find out the most suitable solvent for
the extraction of the ion-pair complex of rhodium(III). It was found that a
0.1 M solution of n-octylaniline in benzene, toluene, xylene provides
quantitative extraction of rhodium(III). The extraction of rhodium(III) was
incomplete if n-octylaniline is dissolved in chloroform (41.1 %), methyl
isobutyl ketone (42.7 %) while no extraction in amyl alcohol,
1,2-dichloroethane, n-butyl alcohol, amyl acetate was observed (Table 4.5). On
safety ground, xylene was preferred to other solvents.
4.4.5 Effect of equilibration time
The extraction of rhodium(III) was studied for various time intervals in
the range of 10 sec - 30 min with 0.1 M n-octylaniline (Table 4.6). 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
rhodium(III) quantitatively. But with prolonged shaking over 10 min there was
decrease in the percentage extraction of rhodium(III) due to the dissociation of
ion-pair complex Hence, in all further studies both the phases were equilibrated
for 3 min (Fig 4.4).
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 84
4.4.6 Effect of stripping agent
Rhodium(III) from organic phase was stripped with two 10 mL
portions of various stripping agents at different concentrations of mineral acids,
buffer solutions and some bases. Rhodium(III) was quantitatively stripped with
hydrochloric acid (1.0 M to 3.0 M), 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) from the organic
phase (Table 4.7). However, percentage recovery of rhodium(III) from organic
phase was found to be incomplete with water and no extraction in ammonia
buffer (pH 10), ammonia and sodium chloride. In recommended procedure,
two 10 mL portions of 1.0 M hydrochloric acid were used for the complete
stripping of loaded organic phase.
4.4.7 Effect of aqueous to organic volume ratio
The extraction of rhodium(III) was carried out in different aqueous
volumes in the range 150-10 mL from 0.03 M sodium malonate medium with
10 mL 0.1 M n-octylaniline in xylene (Table 4.8). There was quantitative
extraction of rhodium(III), 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
throughout the experimental study.
4.4.8 Metal loading capacity of extractant
The influence of the initial rhodium(III) concentration 50-2500 µg on
the extraction by 0.1 M n-octylaniline in xylene was studied. It was observed
that, varying the initial rhodium(III) concentration in the range of 50-1500 µg
has no significant influence on rhodium(III) extraction with the 10 mL of 0.1 M
extractant (Table 4.9). The maximum loading capacity of 10 mL 0.1 M solution
of n-octylaniline in xylene was found to be 1500 µg rhodium(III).
4.4.9 Nature of extracted species
Attempts were made to ascertain the nature of extracted species of
rhodium(III) with the extractant using conventional slope analysis method.
The distribution ratio of rhodium(III) was evaluated at different concentrations
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 85
in molar of sodium malonate at fixed n-octylaniline concentration at pH 6.0
and pH 7.0. A graph of log D[Rh(III)] versus log C[malonate] gave a slope of 1.75
and 1.80, respectively (Fig. 4.5). Similarly, a plot of log-log D[Rh(III)] versus
log C[n-octylaniline] concentrations at a fixed pH 6.0 and pH 7.0 with 0.03 M
malonate gave slope of 1.1 and 1.0, respectively (Fig. 4.6). This indicates a
mole ratio of rhodium(III) to sodium malonate as 1:2 and that of n-octyaniline
as 1:1. Thus, the extracted species was calculated to be an ion association
complex with the probable composition 1:2:1 (metal: acid: extractant). The
probable mechanism of extracted species is as follows,
CH3(CH2)7C6H4 NH2(org) + H + (aq) [CH3(CH2)7C6H4NH3]+
(org) ........(4.1)
Rh3+(aq) + 2C3H2O4
-(aq) Rh(C3H2O4)2
-(aq) .......(4.2)
CH3(CH2)7C6H4NH3+
(org) + Rh(C3H2O4)-2(aq)
[CH3 (CH2)7C6H4NH3+Rh(C3H2O4)2
-](org). .....(4.3)
4.4.10 Effect of diverse ions
The effect of various cations and anions on recovery of rhodium(III)
was investigated. The tolerance limit was set as the amount of foreign ion
causing a change ± 2 % error in the recovery of rhodium(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 rhodium(III) solution in large
excess; 100 mg for anions and 25 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 Ir(III) was eliminated by
masking with oxalate. The anionic species showing interference in the
procedure were EDTA, succinate, thiocyanate, acetate, tartrate, and bromide
due to formation of strong metal complexes (Table 4.10).
4.5 Applications
4.5.1 Separation and determination of rhodium(III) from binary mixture
The separation of rhodium(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
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 86
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
4.11).
Rhodium(III) was separated from these associated metal ions, under the
optimum extraction conditions of rhodium(III) where, all the added metal ions
were remained quantitatively in aqueous phase from which they were
determined spectrophotometrically by standard methods [66-71]. Rhodium(III)
from organic phase was stripped and estimated spectrophotometrically by KI+
SnCl2 method.
The proposed method was also extended for separation of rhodium(III)
from Ir(III) by masking with 25 mg of oxalate. The masked Ir(III) remained in
the aqueous phase quantitatively under the optimum extraction conditions of
rhodium(III). After demasking Ir(III) with 5 mL concentrated hydrochloric acid
with little boiling the solution, it was estimated spectrophotometrically with
stannous chloride-hydrobromic acid method. Rhodium(III) was stripped with
1 M hydrochloric acid and determined as described above.
4.5.2 Separation of rhodium(III) from ternary mixtures
The method was extended to the determination of rhodium(III) in some
synthetic mixtures of associated metal ions. The rhodium(III) was extracted
using the proposed method, the results are presented in Table 4.12.
4.5.3 Sepration of rhodium(III) from synthetic mixtures
A solution containing 200 μg of rhodium(III) was taken and known
amount of other metals were added which are commonly associated with
rhodium(III). Extraction of rhodium(III) was carried out using the method
developed. The results obtained were in good agreement with the amounts
added (Table 4.13).
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 87
4.5.4 Analysis of rhodium(III) in synthetic mixtures corresponding to
alloys
The proposed method was applied for analysis of synthetic mixture
corresponding to alloys such as pseudo palladium (equal amount of Rh(III) and
Ag(I)), iron-rhodium alloy, platinum-rhodium alloy, rhodium- platinum
catalyst. The real samples of these alloys were not available at working place,
which forced us to use synthetic mixture with corresponding composition to
alloys, the rhodium(III) was extracted under its optimum extraction conditions
and determined spectrophotometrically, the results of analysis are reported in
Table 4.14.
4.6 Conclusion
Quantitative extraction of rhodium(III) was achieved in 3 min with
0.1 M n-octyaniline in xylene at pH 9.0.
Trace level of rhodium(III) extracted using low concentration of
n-octylaniline.
Extraction reaction occurred through anion-exchange mechanism.
Developed method is efficient for quantitative separation of
rhodium(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
rhodium(III) from associated metal ions and synthetic mixtures.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 88
Table 4.2 Extraction of rhodium(III) as a function of pH
Rh(III) = 200 μg Aq: Org = 2.5: 1
Sodium malonate = 0.03 M n-octylaniline = 0.1 M in xylene
Equilibrium time = 3 min Strippant = 1 M Hydrochloric acid
(2×10 mL)
pH Percentage extraction, (% E)
Distribution ratio, (D)
1.0 45.3 2.07
2.0 57.6 3.39
3.0 67.8 5.26
4.0 72.3 6.52
5.0 80.5 10.32
6.0 84.5 13.62
7.0 88.1 18.50
7.5 100 ∞
8.0 100 ∞
8.5 100 ∞
9.0* 100 ∞
9.5 100 ∞
10.0 84.2 13.32
* Recommended for general extraction procedure
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 89
Table 4.3 Extraction behaviour of rhodium(III) as a function of
n-octylaniline concentration Rh(III) = 200 μg pH = 9.0
Aq: Org = 2.5: 1 Sodium malonate = 0.03 M
Equilibrium time = 3 min Strippant = 1 M Hydrochloric acid
(2×10 mL)
n-octylaniline, (M)
Percentage extraction, (% E)
Distribution ratio, (D)
0.01 35.1 1.35
0.02 40.4 1.69
0.03 61.1 3.92
0.04 72.6 6.62
0.05 78.9 9.34
0.06 92.1 29.14
0.07 100 ∞
0.08 100 ∞
0.09 100 ∞
0.10* 100 ∞
0.12 100 ∞
0.15 100 ∞
* Recommended for general extraction procedure
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 90
Table 4.4 Extraction behavior of rhodium(III) as a function of weak
organic acid concentration
Rh(III) = 200 μg pH = 9.0
Aq: Org = 2.5: 1 n-octylaniline = 0.1 M in xylene
Equilibrium time = 3 min Strippant = 1 M Hydrochloric acid (2×10 mL)
Acid concentration (M)
Sodium malonate Sodium salicylate
% Ea Db % Ea Db
0.001 13.8 0.39 6.9 0.18
0.005 69.9 5.80 12.5 0.35
0.010 77.6 8.66 62.5 4.16
0.020 93.4 35.37 64.4 4.52
0.025 100 ∞ 65.7 4.78
0.030* 100 ∞ 61.5 3.99
0.035 100 ∞ 59.5 3.67
0.040 83.8 12.93 58.5 3.52
0.050 60.7 3.86 49.3 2.43
0.070 51.9 2.69 41.1 1.74
0.080 46.7 2.19 35.5 1.37
0.090 40.0 1.66 30.9 1.11
0.10 34.8 1.33 28.0 0.97 * Recommended for general extraction procedure a = Percentage extraction b= Distribution ratio
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 91
Table 4.5 Extraction behaviour of rhodium(III) as a function
of diluents
Rh(III) = 200 μg pH = 9.0
Aq: Org = 2.5: 1 Sodium malonate = 0.03 M
Equilibrium time = 3 min Strippant = 1 M Hydrochloric acid (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 41.1 1.74
Methyl isobutyl ketone
13.10 42.7 1.86
n-Butyl alcohol 17.80 No extraction -
Amyl alcohol 13.90 No extraction -
Amyl aceate 13.90 No extraction -
1, 2-Dichloroethane
10.50 No extraction -
* Recommended for general extraction procedure
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 92
Table 4.6 Extraction behavior of rhodium(III) as a function of
equilibrium time
Rh(III) = 200 μg pH = 9.0
Sodium malonate = 0.03 M n-octylaniline = 0.1 M in xylene
Strippant = 1 M Hydrochloric acid (2×10 mL) Aq: Org = 2.5: 1
Time in min Percentage extraction,
(% E )
Distribution ratio,
( D )
10 sec 60.5 3.82
30 sec 72.6 6.62
1 100 ∞
2 100 ∞
3* 100 ∞
4 100 ∞
5 100 ∞
6 100 ∞
7 100 ∞
8 100 ∞
9 100 ∞
10 100 ∞
15 90.1 22.75
30 62.1 4.09
* Recommended for general extraction procedure
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 93
Table 4.7 Extraction behavior of rhodium(III) as a function of
stripping agents
Rh(III) = 200 μg pH = 9.0
Sodium malonate = 0.03 M n-octylaniline = 0.1 M in xylene
Aq: Org = 2.5: 1 Equilibrium time = 3 min
Strippant M / pH Percentage extraction, (% E )
Ammonia 1-10
No stripping
HCl* 1-3
100
H2SO4 1-3
100
HNO3 1-3
100
HBr
1-3
100
Water
-
31.9
NaCl
1-5 %
No stripping
Ammonia buffer pH-10 No stripping
* Recommended for general extraction procedure
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 94
Table 4.8 Extraction of rhodium(III) as a function of aqueous to
organic volume ratio
Rh(III) = 200 μg pH = 9.0
Sodium malonate = 0.03 M n-octylaniline = 0.1 M in xylene
Strippant = 1 M hydrochloric acid Equilibrium time = 3 min (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 92.7 31.74
100:10 62.5 4.16
150:10 45.3 2.07
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 95
Table 4.9 Metal loading capacity of n-octylaniline
pH = 9.0 Aq: Org = 2.5: 1
Sodium malonate = 0.03 M n-octylaniline = 0.1 M in xylene
Strippant = 1 M hydrochloric acid Equilibrium time = 3 min (2×10 mL)
Rh(III), ( μg ) Percentage extraction,
(% E )
Distribution ratio,
( D)
50 100 ∞
100 100 ∞
200* 100 ∞
300 100 ∞
400 100 ∞
600 100 ∞
800 100 ∞
1000 100 ∞
1500 100 ∞
2000 81.5 11.01
2500 39.5 1.63
* Recommended for general extraction procedure
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 96
Table 4.10 Effect of foreign ions on the extraction of 200 μg rhodium(III) at pH 9.0 in 0.03 M sodium malonate with 0.1 M n-octyaniline in xylene
Ratio of ions
Rhodium: ion Mass tolerated, mg Foreign ion
2:500 50 Iodide
2:250 25 Zn(II), oxalate.
2:150
15
Ni(II), Te(IV), Tl(III),
Mo(VI), Se(IV), Ba (II),
Ce(IV)
2:100
.
10
Mg(II), Cd(II),
Sb(III), V(V), Pb(II),
Sn(II), Bi(III), fluoride,
thiourea, Nitrate.
2:50 5 Cu(II), Co(II), Fe(III)
2:20 2 Fe (II), Hg (II), Cr(VI)
2:1 1 Ag (I), Pt(IV), OS(VIII),
Au(III), Pd(II)
2:0.5 0.5 Ru(III), Ir(III)a
a masked with oxalate
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 97
Table 4.11 Separation of rhodium(III) from binary mixtures
Amount of metal ion, (μg)
Mass taken, µg
Average (%) Recovery*
Chromogenic ligand
Ref. No.
Rh(III) Ir(III)a
200 100
99.0 97.4
stannous chloride-hydrobromic acid
[67]
Rh(III) Pt(IV)
200 300
99.0 99.4
stannous chloride-hydrochloric acid
[67]
Rh(III) Pd(II)
200 200
98.8 98.4
4’-ChloroPTPT
[68]
Rh(III) Au(III)
200 200
98.8 97.1
SnCl2
[67]
Rh(III) Se(IV)
200 200
99.0 97.0
4’-BromoPTPT
[69]
Rh(III) Te(IV)
200 200
98.8 98.9
4’-BromoPTPT
[70]
Rh(III) Os(VIII)
200 200
98.0 99.3
Thiourea
[67]
Rh(III) Fe(III)
200 500
99.0 98.8
Thiocynate
[67]
Rh(III) Co(II)
200 500
99.0 98.7
Thiocynate
[67]
Rh(III) Ni(II)
200 1000
99.0 98.9
DMG
[66]
Rh(III) Ru(III)
200 200
99.2 98.9
4’-ChloroPTPT
[68]
Rh(III) Cu(II)
200 1500
99.0 98.7
4’-ChloroPTPT
[71]
*average of five determinations a = masked by 20 mg oxalate
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 98
Table 4.12 Separation of rhodium(III) from ternary mixtures
Metal ion
Amount taken,
μg
Average recovery of rhodium(III),*
% Rh(III) Pt(IV) Pd(II)
200 100 100
99.0
Rh(III) Fe(III) Ni(II)
200 150 100
98.6
Rh(III) Cu(II) Ni(II)
200 150 100
98.6
Rh(III) Pd(II) Cu(II)
200 200 150
99.0
Rh(III) Pd(II)
Au(III)
200 200 100
99.0
Rh(III) Ir(III)a
Pd(II)
200 100 200
98.6
* Average of five determinations a = masked by oxalate
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 99
Table 4.13 Separation of rhodium(III) from synthetic mixtures
Composition, μg Rhodium(III)
found, μg Recovery*, % RSD,%
Rh(III),200;Pd(II),200;
Pt(IV),200;Ir(III)a,100
197.2
98.6
1.4
Rh(III),200;Au(III),100;
Pd(II),200;Pt(IV),100
197.0
98.5
1.5
Rh(III),200;Pd(II),200;
Pt(IV),100;Ru(III),200
198.0
99.0
1.0
Rh(III),200;Pd(II),200;
Pt(IV),100;Ru(III),200;
Ir(III)a,100
197.2
98.6
1.4
Rh(III),200;Pd(II),200;
Pt(IV),100;Ru(III),200;
Ir(III)a,100;Os(VIII),100
197.0 98.5 1.5
* Average of five determinations a = masked by 20 mg oxalate
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 100
Table 4.14 Determination of rhodium(III) from synthetic mixture
corresponding to alloys
Alloys Metal
mass, (µg)
Rhodium(III)
mass found
/(µg)
R*
(%)
RSD,
%
Pseudo palladium (equal
amount of rhodium(III) and
Ag(I)
Rh(III),50 %; Ag(I),50 %
200
198.0
99.0
1.0
Iron- rhodium alloy
Rh(III),74.98 %; Fe(III),
25 %
148
145.9
98.6
1.4
Rh(III),67.71 %; Fe(III)
32.28 %
135
133.1
98.6
1.4
Platinum-rhodium alloy
Pt(IV) 87 % Rh(III)13 %
174 172.2 99.0 1.0
* Average of five determinations R = % Recovery of rhodium(III)
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 101
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10pH
Perc
enta
ge E
xtra
ctio
n (%
E)
Fig. 4.1 Plot of pH versus percentage extraction of rhodium(III)
(200 μg/mL) from malonate medium (0.03 M) by using
n-octylaniline (0.1 M) as an extractant in toluene with 3 min
shaking time.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 102
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 0.14 0.15
n-octylaniline (M)
Perc
enta
ge E
xtra
ctio
n (%
E)
Fig. 4.2 Extraction of rhodium(III) (200 µg/mL) at pH 9.0 from
0.03 M sodium malonate as a function of n-octylaniline
concentration.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 103
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 malonate
Sodium salicylate
Fig. 4.3 Extraction behavior of rhodium(III) (200 µg/mL)as a function of
weak organic acid concentration.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 104
0
10
20
30
40
50
60
70
80
90
100
0.1 0.3 1 2 3 4 5 6 7 8 9 10 15 30Time in Min.
Perc
enta
ge E
xtra
ctio
n (%
E)
Fig. 4.4 Extraction of rhodium (III) (200 µg) with 0.1 M n-octylaniline
at pH 9.0 as a function of equibration period.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 105
▲ Slope at pH 6= 1.75
■ Slope at pH 7= 1.80
-1.5
-1
-0.5
0
0.5
1
1.5
2
-3.1 -2.9 -2.7 -2.5 -2.3 -2.1
Log C [malonate]
Log
D[R
h(II
I)]
Fig. 4.5 Log-log plot of distribution ratio LogD[Rh(III)] versus
Log C[malonate] at fixed n-octylaniline concentration.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 106
▲ Slope at pH 6 = 1.1
■ Slope at pH 7 = 1.0
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-2.3 -1.8 -1.3 -0.8
Log C [n-octylaniline]
Log
D[R
h(II
I)]
Fig. 4.6 Log-log plot of distribution ratio Log D[Rh(III)] versus
Log C[n-octylaniline] at fixed malonate concentration.
Chapter 4 – Solvent extraction studies of rhodium(III) using high molecular weight amine
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur 107
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