Full text of DOI:10.1002/jccs.200200026

JournaloftheChineseChemicalSociety, 2002, 49, 165-172
165
Extraction Behaviour of Cyanex-923 and Cyanex-471X Towards the
Rhodium(III) from Bromide Media and Its Separation from other
PlatinumMetals
S. N. Duche, D. V. Chavan and P. M. Dhadke*
InorganicChemistryLaboratory,AppliedChemistryDivision,DepartmentofChemicalTechnology,
Uni ver sity of Mumbai, Matunga, Mumbai - 400 019, In dia
The ex trac tion of Rh(III) from bro mide me dia with Cyanex-923 and Cyanex-471X in to lu ene was stud-
ied. The quan ti ta tive ex trac tion of Rh(III) with extractants was found by study ing the dif ferentparameters
like,hydrobromicacidconcentration,extractantconcentration,diluentsandeffectoftem peratureonextrac-
tion. Theoptimumconditionwas[HBr]=1.0-1.5moll-1, [SnCl2] = 0.2 mol l-1 with [Cyanex-923] = 0.15mol
l-1, while it was [HBr] = 1.5-2.0 mol l-1, [SnCl2] = 0.4 mol l-1 with [Cyanex-471X] = 0.8 mol l-1 intoluene.The
quantitativeextractionwasobservedonlyinthepresenceofSnCl2 for both extractants. The com plete re cov-
ery of Rh(III) from the Cyanex-923 ex tracted or ganic phase was ob served with the 1:1 mix ture of(4.0 mol l-1
HCl + 2.0 mol l-1 HNO3),and that with the Cyanex-471X ex tracted or ganic phase was found with 1:1 mix ture
of (2.0 mol l-1 H 2SO4 + 1.0 mol l -1 KMnO4). Stoichiometric ra tio of Rh(III) with both extractants was 1:1. The
proposedmethodswereemployedforextractionandseparationofRh(III)fromotherplatin um metal ions and
also for re cov ery of Rh(III) from a syn thetic so lu tion of spent autocatalysts.
INTRODUCTION
Rho dium, a pre cious metal, is used in elec tronic de-
vices, space ma te ri als and as a cat a lyst. Re cently it has been
employedinautomobilecatalyticalconvertersasamonitor
to con trol NOX emission.
Recently, CytecIndustriesInc. Canadahavemanufac-
tured a se ries of organo phos phine com pounds12 which are
mar keted un der the trade name of ‘Cyanex’ like trialkayl-
phosphine ox ide (Cyanex-923) and triisobutylphosphine sul-
fide, TIBPS (Cyanex-471X) which have ‘O’ and ‘S’ as do nor
atoms, andsoareusefulforextractionofclassb(softmetals)
metal ions. Organophosphine sul phide (TIBPS) was used for
extraction of Rh(III) from nitric acid media13 while
Cyanex-923 was em ployed14 for ex trac tion of Au(III) from
HClmedia.
Theextractionandrecoveryofrhodiumisdifficultdue
to its com plex chem is try in chlo ride me dia.1,2,3 Aliterature
sur vey in di cates that though many extractants are used, no
systemissatisfactoryforquantitativeextractionandrecov-
ery of Rh(III) from con cen trated acid so lu tions. So there is a
need to de velop a more ef fi cient and se lec tive pro cess for
separationandrecoveryofrhodium.
Thedistributioncoefficientofplatinummetalionsvar-
iedconsiderably15 by chang ing the acid (HX) ex trac tion me-
dia. When the rou tine chloro com plexes are con verted to
bromo form then they un dergo aquation to a lesser ex tent, en-
abling them to be more eas ily extractable than chloro com-
plexes. Thus the use of bro mide16 me dia has opened a new
pathforextractionandseparationofRhodium(III)andsimi-
lar metal ions. Re cently bro mide me dia was em ployed17 for
quantitativeextractionofAu(III)withtheextractanttriphen-
ylphosphinesulfide.
The amines4 are good extractants for Rh(III) at lower
con cen tra tions of HCl. But in pre cious met als re fin ing, the
-1
HCl con cen tra tion is quite high (4.0 mol l ), so di rect ap pli-
cationofamineswouldbedifficult.TheextractionofRh(III)
fromchloridemediawithquaternaryammoniumsalt6 showed
better re sults than with TOA.5 Pyridinederivatives7 and 8-
hydroxyquininederivatives8 were stud ied for ex trac tion of
Rh(III) from chlo ride me dia and dioctyl sul fides9 were stud-
ied from ni tric acid me dia. Stan nous chlo ride was used for
ex trac tion and sep a ra tion of Rh(III) with triphenyl phos-
phine10 and with Kelex-10011 fromchloridemediafromother
platinumgroupmetalions.
ThepresentworkdealswiththeextractionofRhodium
from hydrobromic acid me dia with new com mer cially avail-
able Cyanex-923 and Cyanex-471X extractants, to ex plore
thepossibilitiesforextractionandseparationofRh(III)from
platinumgroupmetalionsfrombromidemedia.
* Cor re sponding au thor. Fax: +91-22-4145614; E-mail: dvc_pmd@aplchem.udct.ernet.in

166 J. Chin. Chem. Soc., Vol. 49, No. 2, 2002
Duche et al.
-1
EXPERIMENTALSECTION
from 0.1 mol l-1 to 8.0 mol l-1 with 0.15 mol l Cyanex-923
and with 0.8 mol l-1 Cyanex-471X in to lu ene (Fig. 1). Max i-
mum ex trac tion of Rh(III) was 59.7% in the range of 1.0 to
Apparatus and Reagents
-1
G.B.C.-911A UV/Vis i ble spectrophotometer was used
forabsorbancemeasurements. ThereagentsCyanex-923and
Cyanex-471X, kindly sup plied by Cytec In dus tries, Inc. Can-
ada,18 wereusedwithoutfurtherpurification. Accordingto
the prod uct man ual, Cyanex-923 is a mix ture of four trialkyl-
phosphine ox ides with the gen eral for mula R3P(O) (14%),
R2R¢P(O) (42%), RR¢ P(O) (31%) and R¢ P(O) (8%), where
1.5 mol l HBr with Cyanex 923 and 42.4% in the range of
1.5 to 2.0 mol l-1 HBr with Cyanex-471X in to lu ene. The de-
crease in the ex trac tion of Rh(III) at higher acid con cen tra-
tionseemstobeduetocompetitionbetweenRh(III)andHBr
toassociatewiththereagent,whichissimilartotheearlierre-
ported ex trac tion of Au(III).14 How ever the quan ti ta tive ex-
trac tion of Rh(III) was found pos si ble only in the pres ence of
thestannouschloridefrombromidemedia.
2
3
R = n-hexyl and R¢ = n-octyl. Its av er age mol e cule mass is
348 and den sity at 20 °C is 880 kg/m3.
Though the quan ti ta tive ex trac tion of Rh(III) with
Cyanex- 923 in to lu ene from HCl me dia was ob served, it re-
quired two step strip ping with HNO3 for re cov ery of Rh(III).
How ever in the pres ent work only one step strip ping was
foundsufficientforrecoveryofRh(III)frombromidemedia.
Thusbromidemediaismoreadvantageousthanchlorideme-
dia.
Cyanex-471X is triisobutylphosphine sulphide, an
off-whitecrystallinesolidhavingameltingpointof58-59°C
andamolecularmass237.
CH3
(CH3 ¾ CH¾ CH2) ¾ P = S
3
Influence of Stannous Chloride
Be tween the two com mon ox i da tion states of rho dium
are +3 and +1; usu ally the +3 state is dom i nant in con cen-
tratedbromidesolution. Oxideandhalidesformoctahedral
cationic com plexes with Rh(III), which are less la bile1 than
an ionic com plexes, and so are dif fi cult to ex tract. The ad di-
tion of tin(II) chlo ride re duces Rh(III) to Rh(I) which forms a
morelabilecomplexthanothercomplexesofrhodiumdueto
The stock so lu tion of rho dium(III) was pre pared by dis solv-
ing RhCl3 in hy dro chlo ric acid and stan dard ized by known
methods.19 The re quired con cen tra tion of its so lu tion was
preparedbyfurtherdilution.Thestannouschloridesolution
was pre pared in 2.0 mol l-1 HCl. All other chem i cals used
wereofanalyticalgrade.
Procedure
In or der to study the ex trac tion be hav iour, 10 cm3 of
aque ous phase hav ing 5 mg l-1 of Rh(III) with stan nous chlo-
ride in the re quired amount of hydrobromic acid was equil i-
brated with 10 cm3 of or ganic phase con tain ing Cyanex-923
orCyanex-471Xintolueneinaseparatingfunnel. Alldistri-
butionequilibriastudieswerecarriedoutat25.0± 1.0°C ex-
ceptwhentheeffectoftemperaturewasstudied.
The metal ion from the loaded organic phase was
stripped out with vary ing con cen tra tions of dif fer ent strip-
ping agents, and the amount of Rh(III) ion pres ent in the
aque ous phase was de ter mined by the stan nous chlo ride20
methodat470nm.Spectrophotometrically.
RESULTSANDDISCUSSION
Hydrobromic Acid Concentration Dependence
Fig. 1. Ex trac tion of Rh(III) with 0.15 mol l-1 Cyanex-
923 and 0.8 mol l-1 Cyanex-471X in to lu ene in
the pres ence of SnCl2 frombromidemedia.
SolventextractionofRh(III)wascarriedoutbyvarying
the con cen tra tion of hydrobromic acid in the aque ous phase

ExtractionBehaviourofCyanex-923andCyanex-471X
J. Chin. Chem. Soc., Vol. 49, No. 2, 2002 167
strong p acid na ture of SnCl- , which helps the quan ti ta tive
extractionofrhodiumbepossible.
Rh(III) was stud ied for 1 to 30 mins. The quan ti ta tive ex trac-
tion of Rh(III) was achieved af ter 12 mins and 16 mins with
Cyanex-923 and Cyanex-471X, re spec tively. With fur ther
increaseinshakingtime,thepercentageextractionremained
quantitativeupto30mins.
3
The ex trac tion of Rh(III) was stud ied with both re-
agents by vary ing the con cen tra tion of stan nous chlo ride
from 0.001 to 0.5 mol l-1 from bro mide me dia (Fig. 2). The
quantitativeextractionofRh(III)wasachievedinpresenceof
the 0.2 mol l-1 stan nous chlo ride with Cyanex-923 and 0.4
mol l-1 stannous chloride with Cyanex-471X in toluene.
How ever with both extractants, de crease in ex trac tion was
observedwithincreaseinconcentrationofstannouschloride,
which seems to be due to the com pe ti tion of tin(II) with
Rh(III) to form a com plex rather than with the extractants.
Influence of Diluents
The ex trac tion was found to be quan ti ta tive from 1.0
ReagentConcentration Dependence
The per cent age ex trac tion of Rh(III) with Cyanex-923
and Cyanex-471X in to lu ene is shown in Figs. 3 and 4. The
re sults ob tained show that there is an in crease in ex trac tion
with the in crease in re agent con cen tra tion. Ex trac tion was
found to be quan ti ta tive with 0.15 mol l-1 Cyanex-923 and
with 0.8 mol l-1 Cyanex-471X in to lu ene. The na ture of the
ex tracted spe cies was as cer tained from the plot of log D Vs
log [Cyanex-923] or [Cyanex-471X] from dif fer ent con cen-
tra tions of bro mide me dia. The slopes of graphs were nearly
equal to one. Thus metal to re agent stoichiometry ra tio was
found to be 1:1 with both re agents.
Fig. 3. Stoichiometric ra tio of metal to re agent com-
plex of Rh(III) with Cyanex-923 in toluene
frombromidemedia.
Ef fect of Equi lib rium Time
The in flu ence of shak ing time for the ex trac tion of
Fig. 2. Effect of stan nous chlo ride on ex trac tion of
Rh(III) with 0.15 mol l-1 Cyanex-923 and with
0.8 mol l-1 Cyanex-471X in to lu ene from bro-
midemedia.
Fig. 4. Stoichiometric ra tio of metal to re agent com-
plex of Rh(III) with Cyanex-471X in to lu ene
frombromidemedia.

168 J. Chin. Chem. Soc., Vol. 49, No. 2, 2002
Duche et al.
Table 1. Effect of Diluents on Percentage Extraction of Rh(III)
with Cyanex-923 and with Cyanex-471X in Toluene in
the Presence of the SnCl2 from HBr Media
Table 2. Effect of Diverse Ions on Percentage Extraction of
Rh(III) with Cyanex-923 and Cyanex-471X in Toluene
in the Presence of SnCl2 from Bromide Media. Rh(III) =
5 mg l-1
Diluents
Percentage Extraction with
Diverse Ions
Tolerance limit
Cyanex-923
Cyanex-471X
Rh(III): diverse ions
Toluene
Xylene
n-hexane
Cyclohexane
Chloroform
Carbon tetrachloride
99.4
100.0
98.2
95.9
97.6
97.6
99.4
100.0
98.8
94.7
98.8
98.8
Cyanex-923
Cyanex-471X
Na+, K+, Cs+, Rb+, Mg+2, Ca+2,
Ba+2, Sr+2
1:10
1:13
V+5, Mn+2, Co+2, Cu+2, Cd+2
Cr+3, Fe+3, Zn+2, Al+3, Bi+3
Ru+3, Ir+3
1:8
1:7
1:1
1:0
1:20
1:10
1:8
1:1
1:0
1:20
Pt+4, Pd+2, Au+3, Os+8
Cl-, I-, SO3-2, Citrate, Oxalate
mol l -1 HBr in the pres ence of the 0.2 mol l -1 stannouschloride
with 0.15 mol l-1 Cyanex-923 in to lu ene and xylene while
cyclohexane,n-hexane,carbontetrachlorideandchloroform
donotfavourquantitativeextraction.Similarlytheextraction
was found to be quan ti ta tive from 2.0 mol l-1 HBr in the pres-
ence of the 0.4 mol l-1 stan nous chlo ride with 0.8 mol l-1
Cyanex-471Xintoluene, xylene, chloroform, carbontetra-
chloride, and n-hexane while cyclohexane does not give
quantitativeextraction(Table1).
nature.
Ef fect of Stripping Agents
Rh(III)inconcentratedacidishighlyhydrophilicinna-
ture and when ex tracted in the or ganic phase, it is be lieved to
undergo rapid dimerization or polymerization1 and get
locked up in the or ganic phase so its strip ping be comes dif fi-
cult. Since tin(II) chlo ride was used as a reductant in the
quantitative extraction of rhodium(III), its recovery was
made pos si ble only by con vert ing the ex tracted Rh(I) to
Rh(III)bysuitableoxidizingagentswhilestripping.
Influence of Di verse Ions on Per cent age Ex trac tion of
Rh(III)
Rh(III) was ex tracted in the pres ence of a large num ber
of for eign ions with Cyanex-923 and with Cyanex-471X in
to lu ene. The tol er ance limit was set so that the for eign ions
causedinterferenceof± 2% on ex trac tion of Rh(III) with var-
iousmetalions(Table2).Thetransitionmetalions,alkaliand
alkalineearthmetalionsaretoleratedfor> 1:7 to < 1:13 ra tio,
while other no ble metal ions were found to in ter fere dur ing
extraction.
The InfluenceofTemperature
Hexabromocomplexesofrhodiumarethermodynami-
cally un sta ble and hy dro philic in na ture so readily un dergo
aquation.1,2,3
The ef fect of tem per a ture on the ex trac tion of Rh(III)
was stud ied from 303°K to 343°Kfrombromidemediawith
0.15 mol l-1 Cyanex-923 in to lu ene in the pres ence of 0.2 mol
l-1 stan nous chlo ride and with 0.8 mol l-1 Cyanex-471X in to-
lu ene in the pres ence of 0.4 mol l -1 stan nouschlo ride. In both
the cases it was ob served that the ex trac tion of Rh(III) de-
creased with the in crease in tem per a ture. The ef fect of tem-
per a ture on ex trac tion of Rh(III) is ex hib ited in Fig. 5. The
DH value found for Cyanex-923 and Cyanex-417X in to lu ene
Fig. 5. Ef fect of tem per a ture on ex trac tion of Rh(III)
with 0.15 mol l-1 Cyanex-923 in to lu ene in the
pres ence of 0.2 mol l-1 SnCl2 or with 0.8 mol l-1
Cyanex-471X in to lu ene in the pres ence of 0.4
mol l-1 SnCl2 frombromidemedia.
-1
are -42.57 kJmol and -51.70 kJmol-1, respectively, whichin-
di cates that both the ex trac tion re ac tions are exo ther mic in

ExtractionBehaviourofCyanex-923andCyanex-471X
J. Chin. Chem. Soc., Vol. 49, No. 2, 2002 169
Table 3. Effect of Stripping Agents on Percentage Recovery of Rh(III) from the Organic Phase of Cyanex-
923 and Cyanex-471X in Toluene in the Presence of 2.0 ´ 10-1 mol l-1 SnCl2 from Bromide Media
Percentage Recovery
No.
Stripping agents
*Concentration
Cyanex-923
Cyanex-471X
1.0
2.0
4.0
5.0
1.0
2.0
4.0
5.0
1.
2.
3.
4.
5.
HBr
HCl
HNO3
H2SO4
16.2
20.8
32.3
27.3
9.7
27.3
39.4
40.8
37.8
13.0
29.6
57.2
30.5
62.0
7.0
0.0
9.6
10.7
8.5
11.7
3.6
16.0
19.3
9.4
12.6
6.2
28.3
25.4
14.7
14.9
7.2
45.1
19.0
HClO4
1:1 ratio of stripping agents
2.0 mol l-1 HCl +
2.0 mol l-1 HNO3
4.0 mol l-1 HCl +
2.0 mol l-1 HNO3
2.0 mol l-1 H2SO4 +
2.0 mol l-1 HNO3
2.0 mol l-1 H2SO4 +
0.1 mol l-1 KMNO4
2.0 mol l-1 H2SO4 +
1.0 mol l-1 KMNO4
6.
88.8
99.2
81.7
7.
8.
9.
77.8
99.3
10.
* Concentrations are in mol l-1.
The Rh(III) loaded in the or ganic phase was stripped
with var i ous con cen tra tions of strip ping agents like HCl,
HNO3 H2SO4 HClO4, NaOH, NH3, H2O2, Na2S2O3 and KSCN
(Ta ble 3). It was found that NaOH, NH3 Na2S2O3 and KSCN
form an emul sion with the or ganic phase so these were not
used as strip ping agents.
collectors(Cu,Fe,Pb)ortheiroxidesandothersupplements.
The sample solution of spent autocatalyst leach hav ing a
large ex cess of Fe and lower amounts of Mo, Pb, Cu, Ni, Mn,
Co, Cr, Si, Al and P was pre pared syn thet i cally in the lab o ra-
tory,25,26 which was sim i lar to the real one (Ta ble 4). The
chlo ride com plexes of metal ions were con verted to bro mide
byevaporatinganddissolvingtheminHBr.Thesamplesolu-
tionusedfortherecoveryofthesemetalswaspreparedin6.0
mol l-1 HBr.
ItwasobservedthatRh(III)extractedwithCyanex-923
intoluenegotstrippedoutcompletelywiththe1:1mixtureof
(4.0 mol l-1 HCl + 2.0 mol l-1 HNO3). Sim i larly Rh(III) ex-
tracted with Cyanex-471X in to lu ene was stripped out with
Theseparationandrecoveryofrhodium,platinumand
pal la dium from other as so ci ated metal ions was car ried out
by tak ing ad van tage of the dif fer ence in their ex trac tion and
strippingconditionstowardsCyanex-923.Thetolerancelim-
its were set so that they af fected not more than ± 1% on de-
greeofextractionofthisplatinummetalion, undertheiropti-
mumextractionconditions.Mostoftheassociatedmetalions
were pres ent in the lower amounts that are tol er a ble; how-
ever, Fe pres ent in ex cess amounts was found to be quan ti ta-
tively ex tracted with Cyanex-923 at the higher extractant
concentrationof0.05moll -1. In or der to carry out the sep a ra-
tion of Rh(III), Pt(IV) and Pd(II) from each other and also
fromothercollectormetalions, thesamplesolutionwasfirst
equil i brated for 5 mins at 6.0 mol l-1 HBr us ing 1.0 mol l-1
Cyanex-923 and 0.2 mol l -1 SnCl2 when Rh(III) got ex tracted
quan ti ta tively along with Pt(IV), Pd(II) and Fe(III) while
otherassociatedmetalsremainedcompletelyunextracted.
-1
the 1:1 mix ture of (2.0 mol l-1 H2SO4 + 1.0 mol l KMNO4)
andwasdeterminedspectrophotometrically.
Separation of Rh(III) from Ir(III)
Sep a ra tion of Rh(III) from a bi nary mix ture of Rh(III)
andIr(III)wasseparatedwithbothreagentsbytakingadvan-
tage of the dif fer ence in their ex trac tion and strip ping con di-
tions, which are ex hib ited in the Flow Charts 1 and 2.
Validation of Method by Re covering Rh(III) from Spent
Catalysts Leaching So lu tion with Cyanex-923
Spent autocatalysts con tain mainly rho dium, plat i num
andpalladium.SinceCyanex-923hasahighercapacitytoex-
tract Rh(III) than Cyanex-471X, it was used for re cov ery of
Rh(III), Pt(IV) and Pd(II) from spent autocatalysts. The mod-
ules of spent cat a lyst are usu ally melted in the pres ence of

170 J. Chin. Chem. Soc., Vol. 49, No. 2, 2002
Duche et al.
Flow chart 1: For separation of Rh(III) and Ir(III) with Cyanex-923 in
toluene from HBr media at room temperature.
Flow chart 2: For separation of Rh(III) and Ir(III) with Cyanex-471X in
toluene from HBr media at room temperature.
Rh(III) +Ir (III) [1:2 ratio of metal ions]
Rh(III) +Ir (III) [1:2 ratio of metal ions]
1.0 mol l-1 HBr + 0.20 mol l-1 SnCl2
2.0 mol l-1 HBr + 0.40 mol l-1 SnCl2
with 0.8 mol l-1 Cyanex-471X
Shaking time 12 mins.
Organic phase
with 0.15 mol l-1 Cyanex-923
Shaking time 16 mins.
Organic phase
Aqueous phase
Aqueous phase
Rh(III) (99.4%) +
Unextracted Ir(III) (89.7%)
Rh(III) (99.3%) +
co extracted Ir (III) (12.8%)
Stripped with
Unextracted Ir(III) (87.2%)
co extracted Ir (III) (10.30%)
Stripped with
4.0 mol l-1 HCl + 2.0 mol l-1 HNO3
2.0 mol l-1 H2SO4 + 1.0 mol l-1 KMNO4
Aqueous phase
Organic phase
Aqueous phase
Organic phase
Rh(III) determined
co extracted Ir(III) (10.30%)
Stripped with
Rh(III) determined
co extracted Ir(III) (12.8%)
spectrophotometrically (99.2%)
spectrophotometrically (99.3%)
Stripped with
4.0 mol l-1 HClO4
2.0 mol l-1 HNO3
+
6.0 mol l-1 H2SO4 + 4.0 mol l-1 HCl
Organic phase
Recycle
Aqueous phase
determined spectrophotometrically
Ir (III) (12.3%)
Organic phase
Recycle
Aqueous phase
determined spectrophotometrically
Ir (III) (8.4%)
Determined spectrophotometrically
Ir(III) (total 99.5%)
Determined spectrophotometrically
Ir(III) (total 98.1%)
in bro mide me dia from the syn thetic so lu tion of spent auto-
catalyst (Ta ble 5).
The ex tracted Fe(III) from the or ganic phase was stripped
with wa ter. Then Rh(III) was stripped with 1:1 mix ture of
-1
(4.0 mol l HCl + 2.0 mol l-1 HNO3). There af ter Pt(IV) was
CONCLUSION
stripped with 1.0 Na2S2O3 and Pd(II) with 50% NH3. Thus
Rh(III), Pt(IV) and Pd(II) can be com pletely and con ve-
nientlyextracted, separatedandrecoveredwithCyanex-923
Theresultsobtainedshowthatcommerciallyavailable
Table 4. Typical Composition of Collector Metal in the Real Spent Autocatalyst Leach Solution
Component
Conc. in actual Conc. in synthetic Percentage Component Conc. in actual Conc. in synthetic Percentage
sample
%W
sample
recovery
(%R)
sample
%W
sample
recovery
(%R)
mol l-1
mol l-1
Fe(III)
Mo(VI)
Pb(II)
Cu(II)
Ni(II)
66.0
7.0
1.0
0.5
2
75.0
4.5
3.0
5.0
2.0
3.0
2.0
99.9
--
--
--
--
Cr(III)
Si(IV)
Al(III)
P(V)
Rh(III)
Pt(IV)
Pd(II)
0.5
8.0
2.0
4.0
0.1
0.5
1.0
0.6
15.0
5.0
8.0
5.0
--
--
--
--
99.9
98.3
98.3
Co(II)
Mn(II)
2.5
0.5
--
--
1.0
1.5

ExtractionBehaviourofCyanex-923andCyanex-471X
J. Chin. Chem. Soc., Vol. 49, No. 2, 2002 171
Table 5. Tolerance Limit for Rh(III) in the Presence of
Associated Metal Ions Present in Leaching Solution
ex trac tion of Rh(III) from hydrobromic acid me dia. Cyanex-
923 has higher a ca pac ity to ex tract Rh(III) than Cyanex-
471X. This may be at trib uted to the dif fer ence in the sol va-
tion power ex hib ited by the extractants through two dif fer ent
do nors, O and S, to form a com plex spe cies with metal ions.
Though amines4 are ca pa ble of ex tract ing a num ber of
base met als, they can not be used di rectly to ex tract Rh(III) in
pre cious met als re fin ing be cause the acid con cen tra tion is
quite high (4.0 mol l-1). It was found that 8-hydroxy quino-
line8 gives a max i mum of 40% ex trac tion, where as Kelex-
10011 intoluenesuffersfromstrippingproblemsandpyridine
derivatives7 sufferfromstrippingproblemsaswellasserious
coextraction of Fe. Triphenyl phos phine10 gives about 70%
Tolerance limits
1:26
Metal ions
Al+3, Mg+2, Si+4, Mn+2, Co+2,
Cu+2, Ni+2
1:18
1:14
Fe+3, P+5
Cr+6, Pb+2, Fe+3, Mo+6
Aq. phase: 10 cm3.
Org. Phase: 10 cm3
0.15 mol l-1 Cyanex-923 in
toluene.
1.0 mol l-1 HBr + 5.0 mol l-1
Rh(III) + 0.2 mol l-1 SnCl2
phosphineoxide(Cyanex-923)andtriisobutylphosphinesul-
phide (Cyanex-471X) in to lu ene can be ef fec tively used for
Table 6. Ternary Separation of Rh(III) with Cyanex-923 in Toluene from HBr Media
No. Metal
ions
Conc.
m
( g)
Cyanex-923
mol l-1
Extraction condition
mol l-1
Stripping condition
mol l-1
Spectrophotometric
reagent
% R
1.
Pd(II)
Pt(IV)
Rh(III)
Pt(IV)
Rh(III)
Ir(III)
50
100
150
100
100
150
0.10
0.10
--
0.10
0.15
--
5.0 HBr
5.0 HBr
Co-extraction
5.0 HBr
1.0 HBr + 0.2 SnCl2
Co-extraction
2.0 HCl
4.0 HClO4
4.0 HCl + 2.0 HNO3
4.0 HClO4
4.0 HCl + 2.0 HNO3
4.0 HClO4 + 2.0 HNO3
Arsenazo-III (630 nm)22
SnCl2 (403 nm)24
SnCl2 (475 nm)24
SnCl2 (403 nm)24
SnCl2 (475 nm)24
p-nitrosodimethyl aniline
(540 nm)23
99.50
99.40
98.10
99.40
99.20
98.10
2.
3.
4.
Pd(II)
Rh(III)
Ir(III)
50
100
150
0.10
0.15
--
5.0 HBr
1.0 HBr + 0.2 SnCl2
Co-extraction
2.0 HCl
4.0 HCl + 2.0 HNO3
4.0 HClO4 + 2.0 HNO3
Arsenazo-III (630 nm)22
SnCl2 (475 nm)24
p-nitrosodimethyl aniline
(540 nm)23
99.50
99.20
98.10
Au(III)
Rh(III)
Ir(III)
50
100
150
0.10
0.15
--
4.0 HBr
1.0 HBr + 0.2 SnCl2
Co-extraction
2.0 HClO4
4.0 HCl + 2.0 HNO3
4.0 HClO4 + 2.0 HNO3
Rhodamine (555 nm)20
SnCl2 (475 nm)24
p-nitrosodimethyl aniline
(540 nm)23
99.20
99.00
98.10
* Concentrations are in mol l-1.
Table 7. Ternary Separation of Rh(III) with Cyanex-471X in Toluene from HBr Media
No.
Metal
ions
Conc.
m
( g)
Cyanex-471X
mol l-1
Extraction condition
mol l-1
Stripping condition
mol l-1
Spectrophotometric
reagent
% R
1.
Pd(II)
50
100
100
100
100
150
0.10
0.10
--
0.10
0.80
--
6.0 HBr + 0.1 SnCl2
6.0 HBr + 0.1 SnCl2
Co-extraction
6.0 HBr + 0.1 SnCl2
2.0 HBr + 0.4 SnCl2
Co-extraction
50% NH3
Arsenazo-III (630 nm)22
SnCl2 (403 nm)24
SnCl2 (475 nm)24
SnCl2 (403 nm)24
SnCl2 (475 nm)24
100.0
100.0
99.30
100.0
99.30
Pt(IV)
Rh(III)
Pt(VI)
Rh(III)
Ir(III)
1.0 Na2S2O3 pH = 9.0
2.0 H2SO4 + 1.0 KMnO4
1.0 Na2S2O3
2.0 H2SO4 + 1.0 KMnO4
6.0 H2SO4 + 4.0 HCl
2
p-nitrosodimethyl aniline 99.50
(540 nm)23
3.
4.
Pd(II)
Rh(III)
Ir(III)
50
100
150
0.10
0.80
--
6.0 HBr
2.0 HBr + 0.4 SnCl2
Co-extraction
50% NH3
2.0 H2SO4 + 1.0 KMnO4
6.0 H2SO4 + 4.0 HCl
Arsenazo-III (630 nm)22
SnCl2 (475 nm)24
100.0
99.30
p-nitrosodimethyl aniline 99.50
(540 nm)23
Au(III)
Rh(III)
Ir(III)
50
100
150
0.16
0.80
--
3.0 HBr
2.0 HBr + 0.4 SnCl2
Co-extraction
2.0 HClO4
2.0 H2SO4 + 1.0 KMnO4
6.0 H2SO4 + 4.0 HCl
Rhodamine (555 nm)20
SnCl2 (475 nm)24
100.0
99.00
p-nitrosodimethyl aniline 99.50
(540 nm)23

172 J. Chin. Chem. Soc., Vol. 49, No. 2, 2002
Duche et al.
Hydrometallurgy 1996, 40, 135.
extractioninthepresenceofstannouschloride,whilequanti-
tativeextractionwasobservedbyheatingtheaqueoussolu-
tionofRh-Snbeforeextraction.
Proposedextractionmethodsareusedforquantitative
extractionandseparationofRh(III)withotherplatinummet-
als at room tem per a ture with Cyanex-923 and Cyanex-471X
in to lu ene in the pres ence of tin(II) chlo ride; the ear lier most
challengingstrippingproblemofRh(III)canbesuccessfully
solvedbythesemethods.
2. Palmer, D. A.; Har ris, G. M. Inorg. Chem. 1975, 14, 1316.
3. Swaminathan, K.; Har ris, G. M. J. Am. Chem. Soc. 1966, 88,
4411.
4. Dhara, S. C.; Kudryk, I. V.; Cor ri gan, D. A.; Liang, W. W.
(Eds), TMS-AIME. Warrendale. 1984, p 199.
5. Dolgikh, V. I.; Borikov, P. I.; Borbat, V. F.; Kouba, E. F.;
Gindin, L. M. Tsvet Metal. 1967, 40, 30.
6. Work, R. A.; Good, M. L. Inorg. Chem. 1970, 9, 956.
7. Inoue, K.; Yoshizka, K.; Yamauchi, T.; Houdon, M. J. In:
Logdail, D. H.; Slat er, M. J. (Eds.), ISEC’93. Elsevier Ap-
plied Sci ence Pub li ca tions, UK, Vol. 3, p 1287.
8. Benguerel, E.; Demopoulos, G. P.; Cote, G.; Bauer, D. Sol.
Ext. Ion. Exch. 1994, 2, 497.
The meth ods were found to be sim ple for the re cov ery
of these metal ions from the spent autocatalyst sam ples as
it does not re quire use of dif fer ent extractants, nei ther re-
extraction steps nor the use of ion ex change col umns.
9. Fritsch, E.; Gorski, B.; Beer, M. Proc. Int. Conf. Sol. Ext.
1983, Colorado, U.S.A. 199.
10. Mojski, M. Talanta 1980, 27, 7.
11. Shafiqul, A. M.; Katsutoshi, I. Hydrometallurgy 1997, 46,
373.
12. Amer i can Cynamide Com pany, Cyanex-923 Extractant,
1991, Wayne: New Jer sey, USA.
13. Logden, I.; Patel, N. M.; Thornback, J. R. Sol. Ext. Ion.
Exch. 1986, 4, 421.
ACKNOWLEDGEMENT
The au thors are thank ful to Cytec In dus tries, Inc. Can-
ada for sup ply ing Cyanex-923 and Cyanex-471X gift sam-
ples.
14. Martinez, S.; Sastre, A.; Miralles, N.; Alguacil, F. J.
Hydrometallurgy. 1996, 40, 77.
Received September 3, 2001.
15. Mojski, M. Talanta 1978, 25, 163.
16. Dreher, T. M.; Demopoulos, G. P. InternationalPrecious
MetalsInstitute 1998, 22nd, 3.
17. Shetker, P. B.; Gaud, J. S.; Shinde, V. M. Sep. Sci. and Tech.
1997, 32, 1937.
Key Words
Rhodium(III); Cyanex-471X; Cyanex-923;
Separation; Recovery; Spent autocatalyst.
Nomenclature:
18. Rickelton, R.; Boyle, J. Sep. Sci. and Tech. 1988, 23, 1227.
19. Vogel, A. I. ATextBookofQuantitativeInorganicAnalysis;
Longman: Lon don, 1975; 3rd ed., 55.
[ ]=Concentration[moll -1].
[R]=Reagentconcentration.
D=Distributionratio.
%E=Percentageextraction.
%R=Percentagerecovery.
aq. = Aque ous phase.
org. = Or ganic phase.
<Subscripts>
20. Marczenko, Z. SpectrophotometricDeterminationofEle-
ments; Ellis Horwood Ltd.: Eng land, 1976.
21. Tertipis, G. G.; Beamish F. E. Anal. Chem. 1962, 34, 623.
22. Gupta, San J. Anal. Chem. 1967, 39, 18.
23. Westahd, A. D.; Beamish, F. E. Anal. Chem. 1955, 27, 1776.
24. For rester, J. S. Anal. Chem 1955, 27, 1742.
25. Nowottny, Halwachs W.; Schugerl, K. Sep. Purif. Technol.
1997, 12, 135.
26. Mhaske, A. A.; Dhadke, P. M. Hydrometallurgy, 2001, 61,
145.
REFERENCES
1. Benguerel, E.; Demopoulos, G. P.; Harris, G. B.