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25Journal of Siberian Federal University. Chemistry 3 (2011 4) 207-215
УДК 541.183 : 543.426
Kinetics of Simultaneous Recovery of Platinum (II,IV) and Rhodium (III) from Sulfate-Chloride Solutions on some Anion Exchangers
Alexey M. Melnikov and Olga N. Kononova*
Siberian Federal University 79 Svobodny, Krasnoyarsk, 660041 Russia 1
Received 2.09.2011, received in revised form 9.09.2011, accepted 16.09.2011
The paper is devoted to the kinetics of sorption concentration of platinum (II,IV) and rhodium (III) in their simultaneous presence in freshly prepared or stored sulfate-chloride solutions on some macroporous anion exchangers with different chemical structure.
It was shown that the process rate is high, although it is slightly reduced in case of stored solutions. The rate of platinum sorption concentration in the presence of rhodium on investigated resins is higher than of rhodium in the presence ofplatinum. The sorption process was controlled by gel diffusion for all the anion exchangers studied.
Keywords: platinum, rhodium, sorption, kinetics of sorption.
Introduction
To date, the growing demand for platinum group metals (PGM) stipulated their intensive mining and expansion of supplies of secondary raw materials (spent automobile catalysts, catalysts from chemical industry, electronic scrap and wastes of ore-dressing plants on noble metal-containing deposits). Low concentrations of PGM in solutions obtained after breakdown of such raw materials cause the application of sorption methods, known not only for their efficiency and selectivity, but also for environmental safety [1,2]. The successful industrial application of ion exchangers requires not only investigating their sorption properties, but also their kinetic behavior, as the satisfactory rate is one of the essential factors for resins' technological use.
The recovery of PGM from products of processing of secondary raw materials occurs often by means of sulfuric acid and sulfate solutions. In these solutions, platinum and rhodium exist in the form of sulfate complexes, which are more kinetically inert, compared to corresponding chloride complexes, especially of rhodium [1,3]. The sulfate complexes of platinum and rhodium are hardly sorbed and,
* Corresponding author E-mail address: cm2@bk.ru
1 © Siberian Federal University. All rights reserved
therefore, the sulfate solutions of PGM are needed to be activated before the sorption. Basically, the dopes of sodium chloride or autoclave-cured chlorination are used for this purpose [4-7]. However, the addition of hydrochloric acid to sulfate solutions of PGM facilitates the activation of these solutions without any additional expenses. The investigations [1,6,8] have shown that the sulfate complexes of PGM are absent in these systems. Based on that, we considered the recovery of platinum and rhodium from sulfate-chloride solutions as an important matter of scientific and practical interest.
Our previous investigations [6,8] were focused on rhodium recovery from sulfate-chloride systems, however, we did not covered the kinetics of its recovery in the presence of platinum. The present work is devoted to investigation of kinetics of simultaneous sorption concentration of platinum and rhodium from sulfate-chloride solutions on anion exchangers with different chemical structure.
Experimental
For the purpose of investigation, we selected several anion exchangers: AM-2B (Russia), Purolite S 985 and A 500 (Purolite Ltd, U.K.). These sorbents revealed the best sorption properties to PGM in our previous investigations [8,9]. The functional groups of Purolite A 500 are quaternary ammonia base (QAB), Purolite S 985 contains the polyamine groups, whereas the functionality of AM-2B is based on tertiary amino groups (~ 75 %) and of QAB (~ 25 %). The anion exchangers AM-2B and Purolite A 500 are synthesized on the basis of styrene and divinylbenzene (DVB). Purolite S 985 possesses the matrix on the basis of polyacrylate and DVB.
The initial rhodium stocksolutionwithconce ntration 9.709 mmol/L in 6 M HCl was prepared by sintering of metallic rhodium quantity (0.25 g) with 5-fold excess (in mass) of BaO2 [3]. The content of rhodium in the solutionobtained was determined bya gravimetric methodusingsulfuric acidand thiourea [3]. The luitialplaticum stock colution with noiiceiitiat(nn9.6U9mmol/L io6M/fC7wag prepared by dissolution of accurately weighed quantity of H2PtCl6 in concentrated hydrochloric acid [3].
The sulfate-chloride solution wat prepared by addition of sulfuric acid to chloride solution of platinum and rhodlrm. Uheiuitialconconttations of HCl and/d^U indie rolutinur ugteined wsgc equal to each eilaer.
Before uto, anlnu exuheugers wete prepnset aurotdiug lotranCauhmethoUe [10] oettlondcdwiUU 1 M NaCl aiming to convert the resins into the chloride form.
The sorption of noble metals was carried out from sulfate-chloride solutions with different acids concentrations(0.0u - 2.0 moee,). Tlie radio of hycfrechkme aod cdfuric ncinlu was 1 : 1. The iiutca) concentration oCplatinum and ehochom m tlihoesolutiani heat 0.25 macul...
The kimetlc behavior ef fiiinn eeahangeot towaeds phaemuin and rhodium was inve stigaled as follows. The resin auunltele 100.1 g) were mixed with 10.0 mL oV PtlRh ohlaride or sulfatf-chlfride solution, and then the suspensions were intensively stirred at > 800 rev/min. The saturation times were 0.5; 1; 2; 3; 5; 15; 30; 45; 60; 180; 360 and 1440 min. After a certain time period, the resins were quickly filtered off and the concentrations of noble metals in solution were determined spectrophotometrically with tin (II) ehkmde an°poiessiuin b^.e p]. Ucmg Che resTh2obleined,thedtgreeof saturation (F) of the resins ae weCl as 10i prorct) estf(oln mmol/g-s)were calculatedasfollows:
F = Q, (1)
a.
y= f, (2)
where Qt and q0( are the; aaaounts(inmmol)of ptatinum orrhodium sorbed to time f and at equilibrium, respectively; a,- is quantity (in mmol) of platinum or rhodium sorbed lotime U (in s) pei l_gof ttL^ resin.
Then the kinetic curoesweoe plotlsdonthe coor/lnolesF 0 /(b and v = /(,). A/ter that, the halfexchange times (am, (n n) waaertedf rmiinsd at F= t) .5.
The interpretation of oaaultt tn kinsoica wds c^a^ri^d adt usm= theBoad-Adams' melhod [llbd], according tow-idi the Ootmal ltsiFie^oii; soeldtcieai (si, tvas calcotaSed from:
B (i.06)2 • F2
* = —-• (3)
If the process; is;ror^l^ootl(^d byoolOiffus)on,the funcSson Bt ,/(0) sbould be linnso. Thedifbesion
coefficients (Sf, la) om2Sst core catculsied acaondrng tsr olie e/uation: r i
D = —T-, (4)
4tt ■ tVi
where r is radius ofaesin gram din cm).
The results obtained in ths present work were subjected to slstiitiralpaoasscing accordcng to procedures il4,lS]. Thy rverage oppecimvntal error was less than mi %.
Resutte andi discussion
It; lis known[l,3] ihnt sitilf^t^ contain the oarsed ionir fortt^ !=> of pletinum and rbrdium.
Teereare oery stable ^Ocmeaic aqdabadnobn-complexos as well ae palynurienr aic^uialiib'di"t^?to-!5ulf^t(;^,
smchas ep/^mns^caorjj10, mor^o^ed0^]01 [mA-niorbioxtrsij'l^ en .
TT^i^ presanco 0):' nGM rulfate aamplexro in solutincs oausea ete yconoanced compCication durtno s-^t^cje^^^ oi Chese matnlSi givsn tisat Oiie mcjoaitp ot analytic! mktiirds fon oodOn mebaSs sseoju^raLt^yDJ-are dovelopoi 9oo chloride snirrmo. dbs, cannot 0e usod for sulfuric acidmedta, Ceccusethekinekic inerteesc of PGM sulfate compleaea in hftiher ehfn tvertneis of chlorideones. nortCCsreasoc, these softiooh ohoudl be aetivelsd bo eddmg eodiem cttilorriiil^ or tsy auiodavf-corecC chCorinat-on. Howeves, nfw it n founo than suhfaCescManide roiutionk supvrsrdf tae actiantion of sulfate sohstions, a:ndl(i£;!siLi[;l.t:;!t, Ohlsprocere is rathei rfr'i:01].
Baesd on 3hc hOectcon oboorptlon spnbden of intiat it) t nut nnifarc-cUkmda iolotionn onU oei tile data fvam sefereece 21) have nUOenmmfd thatboI.li freshly prepared solutions and solutio ns stored o^^ci:^ 1 moethn oil not coolaen pullfatc nonrniexas ^zf4ehese mtta(s. ^^^ ^:ti(or:id^ compiront, rncX bt [d/CCUt [RhCl6 ]3", [Pt(OH)Cl5]2i, [Pt{OH)6f-, [Rh(H]O)2Cl4]- etc., are pre sent in the system. During a storage of tiiose selotione, the aquachloro- and hydroxocomplexes of platinum and rhodium, for example, [Pt(H2O)nCl6_nr\ [nr(C0rf)sC76_J2-, [Rh(WH)nCl6 nY 3, SRh(r0rO)tCS6_„r3 , where n = 1-6, arrivein Ithi^se mediaasaresultofhydrolysisandaquation(the so-called"ageing"processes)[1].
We J:i£rs^ie studied in our previous work [9] the ion exchange equilibria and kinetics of simultaneous sorption concentration of platinum (II,IV) and rhodium (Ill) from freshly prepared and stored chloride solutions on some anion exchangers. We have determined that the resins possessed good kinetic
propertiSSgjVil TiSSrHgRereraTyiRlgRTption of noble metals
from sulfate-c^^^^^^^^^g^^^^^^^^^l^i^^ gpeEaHfljSSiE' Pt /Rh sorption from chloride systems, proving the selectivity oftheusedresins.
The data on kinetic investigation of platinum and rhodium sorption from sulfate-chloride freshly prepared solutions on example of anion exchanger Purolite A 5200 are presented in Fig. 1. The kinetic dependencies for the other resins are similar to these curves. It can be seen from these data that the anion exchanger studied possess good kinetic properties, since the process rate is high. For instance, over a period of 20 min, the resins are saturated on average with platinum complexes to (59 - 79 % and with rhodrumions to 57 - 76 % Orom their total exchaoge capacity. For comparison, these resins are saturated in 20 min to 53 - 80 % and 38 - 77 % with platinum and rhodium, respectively, while their sorption proceeds from chloride media.
u-105, mmol/g s
12 n
10 -
a)
4 -
2 -
0
0 200
ti>105, mmol/g s
8
400
600
800
1000
1200 t,S
b)
200
400
600
800
1000
120 t, s
Fig. 1. Kinetic dependences of rates of sorption concentration of platinum in the presence of rhodium (a) and of rhodium in the presence of platinum (b) on anion exchanger Purolite A 500 from freshly prepared sulfatechloride solutions with different acidity 1 - 0.01 M HCl / H2SO4; 2 - 0.1 M HCl / H2SO4; 3 - 2.0 M HCl / H2SO4 (C(Pt) = C(Rh)) = 0.25 mmol/L)
Alexey lei. Melnikov and OlguN. Kononova. ICineititts of Simu ltaneocp Recovery of Platinum (II, IV) and Rhodium ( III)...
The rvte of sorption concentration in weat acidvoluttons is iiighao than in strong acid ones. Such yehavior of strong txusic aruon exchomger murolitn A 50y aax be tcplainedlny competition bntween cxmpleo aniynr o0 Sldlum anci peiat^oiaisiyio and cMOTado dons during ion cxchange froness. ^ooi")"«:e>s50ie<ilinoo^;ii^ <ov ktseo tiop conecnOration of Cl~ - ionn i( in tolntion, the weatee r in laii^re eompetinr entiryct^. As a resit, an iteci^^^p<p in Pe/R0 sosoeiic^n iisi obsetved.
Ac for nhe wook baskc r^sitn Inurx)i^V(( <5 98e end mtermediate anitrn AM-0)Ee they bbhuve
slmclarha, r.y iticoir vocption aXctlVy tdo-^ixurdis PiiRO vompioxet ^liows^ with alc^elvei^^^^iii^n^cidity of tontecaing soiutinn. This effect can Os expMned Ih^^xhtelnt^stns^e in deprotonation of the nitrogen atom in fnacllonai amixn gapup,wXieO inl;reacec tXe compiuxation xbiiity of thesesorbents [16].
It should tie also noted that the recovery of platinum and rhodium from strong acid solutions proceeds with high process rate. Thy lower rete ofrhorium (HS rorfrtian tin eUie present of ^aiieum (njVt cpo be vnpMned bx ]-LlegJnr^r kmetio iinis^li^ciis clf tis ehkiaide ^^mja^^etet:^ esneeie[ly m wnul oeid t nlationS] I^ti^ls. nown liiXi tliattiie honera° led ehvlgid aqua onmplxxnr SRh(HrO)3Ce3] 0,[CO (HlO)2Cl4]", IR^H 20 )C/5]2ixie ^ene! ]p such ootutioxs.
Thl ntudy oti kioetlcs of Pt /Rh sorption from stored sulfate-chloride solutions is of special inteeest, because these solutirnn are often usod iy tHr^e iiic]usnhr dudmia ]:><lj[ttrrecor^^igLLTli]ig^r^ ou^n^ne<r (Tablel) show that theratv o. sounieoie ironi eoiut<ona,stoeea ovey2 megthc< decrea seum rompariroe wilh fresMyprepRred one u Tina coin be i^ei^ji^LEiaLin^cl Tony focmation ne lo^ie^itli]^llie- hy0roxo- and aqua eroi^{i<e?iee ofnlatinnmofd alodium. However, atc the wiolu, tlie; rete of Pt/Rh recovery from stored solutions remains on a high level. Thus, over of 20 min, the anion exchangers investigated are saturated from their total exchange capacity on the average to 51 - 60 % and to 35 - 46 % by platinum and rhodium, respectively. These values correlate with the results, which we have obtained earlier for pdloride ttoied no lutionc (45 - 59 % anrl P4 - 55 % fof Pt end Rh, respectively).
Ii Ran be xivo hrom the dita precofted en Ta°]e Pahat rde sorption concentration process proceeds with the rate of order of 10-5 mmol/g-s. The half-exchange time in the case of Pt recovery is much shorter than for Rh sorption. Therefore, the kinrtic parameters are in agneement with our insight into ip9 sdeltioity xfmvestigated anionexchangevs.
Ii oanbc ake isen leom pnbla gfhat tpe aaerefila^sriitg eoebint Purolite S 985 reveals the best kinetic fRopextiet among the studkd rescti owing to tns £it»i1:is^;>i nfoi: simolteneous iil oeelvnge asid comploe SnanaeSivid ix wv ak cclilris; metiei .
Wirhthe sPieene oC FsiPti soiutions, the sorption rate decreases, the half-exchange time is longer OPcm casa oi brcii^Stlytni-^caeceb tc^lulic^iss. e*Sc c onsiber ilt ttiebos pteee beoatsse of formation of kinetically ipert comeleoei rf aoble cos^aCe.
it shouip See nvtvd ihat soes>tivn of piatlnem unV riiodlum fiiom stored suifatevchloriUe roiueione proceeds with higher rate than the rerooeey of t2ese meSs^lis fsomlfored cgloridemedf whereat in freshly prepared systems the ratei oit fhese frocesyes alt afmoai ecjetol. Probebly -hlr pdiinmeooci ean be tvplomad bylesserexposure tohydrolysis in sulfate--chloride solutions than in chloride systems.
Thv kmetios tyj> e firing sc^riit^oi^sob^bti9tis)n op platinumanp rftedmmfrom freshly prepared an° stored! sutfaie-fhkmilesolutione ^as delernunod ucitlll ties das eilid Bo^iAdamt' modelwiie ihe te rt^es^^vi^^idgh rltu]^ia[l1-:leCC• aigg the dependencies Bt = fti goo ecl(^n
Purolite A 500, which are consisted wish UlC^e ct)tl^l^i^lc^^lfben ¿«l iain(eiier i^f iog ^j^l^lrfiii^is.
These dependencies for the other sorbentl inf^st^il^^is^ el^o ainn;^r. Teserel'ore, Ide Pt /Rh sorption
Table 1. Kinetic parameters of simultaneous sorption concentration of Pt (II, IV) and Rh (III) from freshly prepared and stored chloride and sulfate-chloride solutions (C(Pt) = C(Rh) =0.25 mmol/L, C(HCl) = C(H2S04) =0.01 mol/L)
Trade name Kinetic parameters Chloride solutions Sulfate-chloride solutions
Freshly prepared Stored Freshly prepared Stored
Rt Rh Rt Rh Rt Rh Rt Rh
Purolite A 500 A/2 ' S 306 658 1270 1364 159 189 583 1055
D-Nf,cm1 Is 5.18 2.41 1.25 1.16 9.97 8.38 2.72 1.50
v-105 mmol / g ■ s 2.80 1.23 0.72 0.54 5.07 3.66 1.08 0.81
Purolite S 985 h/2 > s 174 182 572 639 157 185 289 945
D-10s, cm1 / s 9.11 8.71 2.77 2.48 10.09 8.57 5.48 1.68
v-105 mmol / g ■ s 6.41 3.76 1.63 1.34 7.31 3.92 2.28 1.11
AM-2B Kn ' s 307 488 1.62 1340 162 246 496 1264
D-I0s,cm2/s 13.21 8.31 3.21 3.03 14.09 9.28 8.18 3.21
v-105 mmol / g ■ s 2.98 2.02 0.74 0.59 5.46 2.99 1.32 0.78
Bt
0 10 20 30 40 50 &0
t, min
¡¡eH .gHgBSgHfflHpOf UmRHgfli ^^¡^^^¡^^ESP-^^^^m^lBi diffusion kinetics of Pt / Rh sorption from sulfate-chloride solutions on anion exchanger Purolite A 500 1 - Pt in the presence of Rh (freshly prepared solution); 2 -Rh in the presence of Pt (freshly prepared solution); 3 -Pt in the presence of Rh (stored solution); ?l w!lfflffBffilliuBKm ElSffSlJlffffWTO (SUeBEhlligl BOMBl(WSB C(HSO4) =0.01 mol/L)
n
-ft
Fio .3. Dependences of saturaeion degree ton V/during Ptietie sorption feomsulfahe-chloridesolutions on anion exchanger Purolite A 500 1 - Pt in the presence of Rh (freshly prepared solution); 2 - Rh in the presence of Pt (freshfy prejrared solution); 3! - Pt in thepresance of nh fstoredaoletion)^ _ Rhm 1;he presence of Pt (stored
¡¡hgeiiSiUd-^ I
is conrroUedby ^ chiffuikm f.d. inPer-dtffuskjnofkmeexchap^id inaoesm benp).The dependencies
aesnj^
aren-t o i ^asECSB n^n^e^aSCndt,liSp lOdfPEiSCDirHsEEEEOePlPEOnPwEBUS fusion
mme
Ih fhnuld ire noted idai kinetira typn during Pt /Rh sorption from sulfate-chloride freshly prepared and "aged" solutions on anion exchangers investigated is in agreement with gel kinetics during sorption of thesemetal complexesfrom chloride solutions,whichwe have studied inourprevious work [9].
- 213 -
The main kinetic parameters of simultaneous Pt / Rh sorption are summarized in Table 1. The average diffusion coefficients are of the order of 10-8 cm2/s. Their values are higher for platinum sorption in the presence of rhodium, than for rhodium sorption in the presence of platinum under the same conditions. Such order of diffusion coefficients is in agreement with the data obtained for kinetics on selective ion exchangers [11,12,16].
Conclusions
The simultaneous sorption concentration of platinum (II,IV) and rhodium (III) from freshly prepared and stored sulfate-chloride solutions was investigated in dependence on initial concentrations of hydrochloric and sulfuric acids. The high rate of this process revealed in freshly prepared solutions, is decreased slightly in stored solutions. The rates of platinum sorption in presence of rhodium on the anion exchangers investigated are greater than the rates of rhodium sorption in presence of platinum under the same conditions. The whole ion exchange is controlled by gel diffusion for all the studied resins.
The results allow recommending the anion exchangers Purolite S 985 and A 500 as well as AM-2B for application in improved technological schemes for utilization of spent platinum-rhodium catalysts.
References
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Кинетика совместного извлечения платины (ПДУ) и родия (III) из сульфатно-хлоридных растворов на некоторых анионитах
А.М. Мельников, О.Н. Кононова
Сибирский федеральный университет, Россия 660041, Красноярск, пр. Свободный, 79
Изучена кинетика сорбционного концентрирования платины (II,IV) и родия (III) при совместном присутствии из свежеприготовленных и выдержанных сульфатно-хлоридных растворов некоторыми макропористыми анионитами различной химической структуры. Показана высокая скорость протекания этого процесса, которая несколько снижается при выдерживании растворов. Скорость сорбционного концентрирования платины в присутствии родия на исследуемых сорбентах превышает таковую для родия в присутствии платины. Сорбционный процесс контролируется гелевой диффузией для всех изученных анионитов.
Ключевые слова: платина, родий, сорбция, кинетика сорбции.
