Optimization of Pt and Pd Displacement Process of Au Reduced Solution

稀有金属990214稀有金属资源系统RARE METALS数字化期刊WANFANG DATA ( CHINAINFO)DIGITIZED PERIODICAL1999年第2期No.2 1999Optimization of Pt and Pd D isplacement Processof Au Reduced SolutionHuJianhui(胡建辉)Guixi Smelter, Jiangxi C opper Corporation, Guixi 335424, ChinaReceived 2June 1998AbstractThe question existed in the displacement of platinum and palladium fromAureduced solution was analyzed. The process optimization schemewas put forward and adoptedto practice and has achieved a good result.Key W ords.: Pt and Pd, Displacement Optimization1. IntroductionIn Guixi Smelter, copper anode slimewas treated by means of technological process ofvolatilizing Sein a rotary kiIn, picking copper in water solution, leaching Tein alkalinesolution,separating Au by chloridizing method and extracting Ag with sodium sulphite. The Pt and Pd incopper anodeslime was almost concentrated in Au rich solution after the Au reduced withNa2SO3 and then recovered by means of traditional displacement with zinc ingot, as seen in Fig.1.The reduced solution with ahigh acid concentration solution contained many foreign ions.The static state displacement wasvery low in efficiency and the reagent consumption wasverygreat. In addition, the displaced solution could not meet the discharged standard and a greatamount ofbase metals(such as bismuth) got into the displaced residue making it more difficult toextract the Pt and Pd. The chemical composition of Au reduced solution is shown in T able1.中国煤化工MHCNM HGfle://E Viy999yji9902/990214.htm (第1/ 8页) 2010-3-23 12:17:16稀有金属990214Au reduced solution↓Zinc ingot displacementDisplaced solution. Pt and Pd concentrateFig.1. Flowsheet of Pt and Pd displaced.2. Process ModificationPt and Pd existed in formofPtCI42- and PdCl42- in Au reducedsolution. The following reactions were proposed in theprocess.Table 1. Static state displacement resultsElementsAu| Pt| PdBiCu | Sb |Hz2SO4Aureduced slution/mgL-1|25.0 6.0 14.04321164 6.0 7200Displaced solution/mgL-1 3.0 1.2 2.5 | 601150<5.0 48000Pt and Pd concentrate/% 1 .50|0.210.75 65 0.55 0.6PrCL2- + Zn= Zn2+ +4C1- + Pt(1)PdCL2- + Zn= Zn2+ +4Cl" + Pd .(2)2AuCL2- + 3Zn= 3Zn2+ +8CI- + 2Au(3)2Bi+ + 3Zn= 3Zn?+ + 2Bi (4)2H*+Zn=Zn2++H2↑(5)P+ H+ + 3C1~ + HCIO= PrCL2-+ H20(6)Pd+ H* + 3C1- + HCIO = PdCL.2-中国煤化工<7)Zn+ HCIO+ H° = Zn2+ + CI~MHCNM HG+ H2O(8)fle://E/ Vy999yji9902/990214.htm (第2/ 8页) 2010-3-23 12:17:16稀有金属990214The reaction (4) not only increased the zinc consumption but also degraded the Pt and Pdconcentration. C omparing the hydrolysis pH values of Bi3+, PtC l42-~ and PdCl42-, Bi3+ can be .separated by hydrolysis from theAu reduced solution before it was displaced when adjusting theacid concentration of the solution[ 1] .PICL2- + 2H20=2H+ + 4CI-+ P(OH)2(9)pH=4.29- 1/21g[ PCL2- ]+ 2lg[Cl- ]PdCL42- + 2H2O= 2H+ +4CI~+ Pd( OH)2(10)pH = 5.18 - 1/21g [ PdCL3- ]+ 2lg[Cl~ ]AuCl4~ + 3H2O= 3H* + 4Cl-+ Au( OH);(11)pH= 7.68- 1/31g[ AuCl4~ ] +4/31g[ C1~ ]Bi++Cl~+H2O=BiOCI+2H°(12)pH= - 1.39- 1/21g[ Bi}* ]- 1/21g[ CI~]Though it is beneficial to the hydrolysis of bismuth and displacement of Ptand Pd byreducing the acid concentration of theAu reduced solution [ 1,2] . Pt and Pd would loss onhydrolysis if thevery low acid concentration was directly adopted. Therefore, bismuth wasseparated firstfrom Au reduced solution by alkalinehydrolysis, followed by adjusting the acid concentration of solution, Pt and Pd were cemented, asshown in Fig.2. Not only could bismuth be separated first from it but also the rates of thereactions(5) ~ (8) and the zinc consumption were reduced. It has also been ableto raise thedisplacement efficiency and achieve quantitative displacement of the Pt and Pd.3. Optimization ofT echnological C onditions3.1. Bi Hydrolysis Precipitation中国煤化工.HCNMHGFig.3 indicates the effect of the acidity on Bi hydrolysis at differentuenprauits.11increase in temperature isDischarge after purified beneficial to Bi precipitation[3] . A reductionfle//E/ Vy/ys9902/990214.htm (第3/ 8页) 2010-3-23 12:17:16稀有金属990214in the acid concentration of the solution is beneficial to the reaction(12) and Bi precipitation.When the concentration of H 2SO4 Was as low as 15 g/L and thereaction temperaturewas above80°C, the precipitation eficiency of Bi was greater than 98%.Au reduced solutionBi hydrolysis precipitationBiOCIBi precipitated solution↓Adjusting acid concentrationCemented with zinc. powderPi and Pd concentrateDisplaced solutionDischarge after purifiedFig.2. Flow sheet of the Pt and Pd displacement optimized.1003\ 2\958515202S中国煤化工Cooentretion d H:SO2 Solutiov/g*l.'FYHCNM HGfle://E Viy999yji9902/990214.htm (第4/ 8页) 2010-3-23 12:17:16稀有金属990214Fig.3. Effect of acidity on precipitation eficiency of Bi.1- -40°C ; 2- 60°C ; 3- 80°CAt 80°C, the process of bismuth hydrolysis affects the Pt, Pd etc, as shown in theTable 2.Only at the solution pH value of above4, PtCl42- would start to be hydrolyzed. Table2 showsthat, when the H 2SO4 concentration of solution was adjusted to 12 ~ 15 g/L during bismuthhydrolysis, AuCl42- and PdCl2- was hardly afected, but PtCI2- has a ltloss and thereasonwas to be studied.T able 2. Effect of acidity on concentrationof Pt et al/mg'L-1No.Au|Pt|Pd| Bi | Cu H2SO410 23.14.716.241121190 800002 23. 14.715.8466 1183 300003 23.04.615.8 167 1146 220004 23.04.315.690 1185 16000「 522.84.015.6 61[1182[ 12000[ 6 22.83.915.3 31 1182| 100007 21.71.713.8 5 1113| 2400①Au reduced solution3.2. Displacement by Zinc PowderIn Au reduced solution, Pt and Pd were displaced with zinc powder very quickly, thereaction equilibriumwould reach for 5 ~ 10 min with agitation. Asseen in Fig.4 and Fig.5.中国煤化工MHCNM HGfle://E Viy999yji9902/990214.htm (第5/ 8页) 2010-3-23 12:17:16稀有金属990214100等805意70H600305070110T'ime t/minFig.4. Effect of time on rateof Pt displacement.1一pH=3;2- 4.9g/L;3- 49 g/L_2写80310790'Time t/min中国煤化工MHCNM HGfle//E Viy999yji9902/990214.htm (第6/ 8页) 2010-3-23 12:17:16稀有金属990214Fig.5. Effect of time on rate of Pd displacement.1一pH=3;2- 4.9g/L;3- 49 g/LIf the acid concentration was toohigh, the redissolution of Pt and Pdwould occur during being displaced lately because the reactions(6), (7) existed. When final pHvalue of the solution was above 3.0, it would be of benefit to restrain the redissolution of Pt andPd. But alot of the hydroxide(such as copper, zinc etc) would be produced at highpH [3],leading to reduction in the gradeof Pt and Pd concentrate and difficult filtration. T he final pHvalue of the solution was recommended to be4.5.Cu(OH)2+ 2H+=Cu2+2H20(13)pH=4.604Zn(OH)2+ 2H+=Zn2+2H2O(14)pH=5.85In aword, adjusting the acid concentration of solution to 12 ~ 15 g/L H 2SO4 at 80°C, theprecipitation eficiency of bismuthwould be above 98% and controlling the final pH valueofsolution at3.0 ~ 4.5, the displacement efficiency of Pt and Pd would be above 98%.4. Commercial PracticePt and Pd displacement achieved a good result after the technological process wasoptimized in commercial practice. Seeing Table3.The practice indicates that owing to optimizing the Pt and Pd displacement process, theconsumption of zinc is as only 15% as that of the former, the by- product BiOCl which contains79% Bi isachieved, the grade of Pt and Pd concentrate rises greatly, the concentration of preciousmetals in the displaced solution is controlled to be 1 mg/L.T able3. Results of Pt and Pd displacement process optimizedElementsAu| Pt| PdBiCu| SbH2SO4Au reduced solution/mgL-1 21.36.0 15.0 43211264 6.0 72000Displaced Bu solution/mgL-121.3 5.5| 14.681 1100 5.014000Displaced solution/mg:L- 1<1<1| <1<5 1090 <5 pH=3.5|BiOCI/%8 g/t90g/t17g/t79.| 中国煤化工Pt and Pd concentration/% 7.0 0.92[3.41[ 30MHCNMHGfle://E/ Viy999yji9902/990214.htm (第7/ 8页) 2010-3-23 12:17:16稀有金属9902145. C onclusionThe process modification and optimization of Au reduced solution in which Bi wasprecipitated prior to Pt and Pd cementation with Zn powder after theacid concentrationadjustment could raise the grade of Pt and Pd concentrate, make the precious metalsconcentration in displacedsolution reach the national dischargedstandard, gain the hy-product BiOCI (contained 97% BiOCl) and save the production costgreatly.References1 Lu Yiyuan, Bing W anda. The Metallurgy of Precious metals, C hangsha: The Press ofC entral South University of T echnology, 1990 (in C hinese).2 Li Dingxing et al. The Extraction and Refinement of Precious metals. Changsha: The Pressof C entral South University ofT echnology, 1991 (in C hinese).3 Zhong Z huqian, Mei Guangui. H ydrometallurgical Processes. Changsha: The Press ofC entral South University ofT echnology, 1988 (in C hinese).中国煤化工MHCNM HGfle://E/ Viy999yji9902/990214.htm (第8/ 8页) 2010-3-23 12:17:16