ON THE DISSOLUTION BEHAVIOR OF RHODIUM IN THE Na 2. O-SiO 2

Transcription

1 J Min Metall Sect BMetall 49 () B (013) Jurnal f Mining and Metallurgy, Sectin B: Metallurgy EFFECT OF Al, MgO AND CuO X ON THE DISSOLUTION BEHAVIOR OF RHODIUM IN THE SLAGS C Wiraseranee a,*, T Yshikawa b, TH Okabe b, K Mrita b a Central Research Institute, Mitsubishi Materials Crpratin, Japan b The University f Tky, Institute f Industrial Science, Tky, Japan Abstract (Received 1 December 01; accepted 17 June 013) Aiming t ptimize rhdium recvery in the high temperature recycling prcess by minimizing rhdium lss int slags in an xidizing atmsphere by cntrlling slag cmpsitin, the effects f representative slag cmpnents, such as Al, MgO, and, n the disslutin behavir f rhdium int the slags was investigated The slubility f rhdium was measured by equilibrating the sdium silicate based slags with pure slid rhdium at 1473 K in air Cnsidering that rhdium disslved int slags as 15, the effect f the xide additin n the activity cefficient f 15 in slags was determined The disslutin f rhdium in slags was suppressed by the additin f Al and MgO, where Al behaved as an acidic xide and MgO behaved as a diluent f slag basicity at a fixed O/SiO rati f 097 The cntent f cpper in slid rhdium equilibrated with the bearing slags slightly increased with increasing cntent f, and was fund t slightly enhance the disslutin f rhdium Rhdate capacity f all slag systems increased with increasing ptical basicity, suggesting that the crrelatin between rhdate capacity and the ptical basicity enables the estimatin f the cntent f rhdium in slags f which thermdynamic prperties f rhdium are nt clarified Key wrds: Rhdium; Platinum grup metals; Slubility; Mlten slag; Thermdynamics; Recycling Intrductin Rhdium is extensively used as a key material in varius specialized applicatins, such as catalysts in autmbiles, high crrsin resistance cntainers fr mlten glass, and high electrical cnductive layers in electrnic devices In recent decades, the wrldwide scarcity and high price f rhdium make the recycling f rhdium essential [1] Because rhdium is chemically inert, the recvery f rhdium frm scrap using liquid cpper r liquid irn as a cllectr metal has been ne f the majr recvery methds [4] In the prcess, rhdium in scrap is cllected int the cllectr metal after melting the scrap with fluxes and the cllectr metal in a reducing atmsphere Then, a rhdiumrich ally is btained as a prduct when the cllectr metal is partly remved int slags by xidatin Theretically, rhdium is rather stable as a metal at high temperature Hwever, lss f rhdium int slags during xidatin in a highly xidizing atmsphere can be critical Thus, the prcess cnditins must be carefully cntrlled in rder t minimize the lss f rhdium int slags Previusly, it was fund that the disslutin f rhdium int slags was apparently influenced by slag * Crrespnding authr: cwira@mmccjp DOI:1098/JMMB111018W cmpsitin [5] This suggests the minimizatin f rhdium lss int slags by cntrlling slag cmpsitin can be viable In rder t effectively cntrl slag cmpsitin, the effects f xide cmpnents in slags n the disslutin behavir f rhdium in an xidizing atmsphere is needed t be clearly understd In the recycling prcess, the cmpsitin f recycling slag varies with the cmpsitin f scrap materials, fluxes, and xides f the cllectr metal Spent autmbile catalysts have been the majr surce fr rhdium; hence, MgO, Al, and SiO frm the hneycmb structure (crdierite, MgO Al SiO ) can be the majr cmpnents f the recycling slag Mrever, by the xidatin f liquid cpper (ie the cllectr metal), bth Cu O and CuO are likely t cexist, and the cntent f a mixture f cpper xides ( ) in slags can be relatively high The effects f Al and additin t slags n the disslutin behavir f ther platinum grup metals were investigated in previus studies The slubility f platinum in the CaO SiO slag (at a fixed CaO/SiO mle rati f 107) was fund t increase with increasing cntent f Al at 1873 K [6] The slubility f ruthenium in the 50 O 40SiO 10Al slag was higher than that in the MOLTEN1 Cnference Special Issue Ninth Internatinal Cnference n Mlten Slags, Fluxes and Salts

2 13 C Wiraseranee et al / JMM 49 () B (013) O50SiO slag at the same xygen partial pressure at 1473 K [7] Furthermre, when the CuRh r CuPt binary allys were equilibrated with the Ca Fe slag at 1573 K in air, it was fund that the cntent f either rhdium r platinum increased significantly with increasing cntent f cpper in slags [8] In the present study, in rder t design slag cmpsitin fr the recvery f rhdium using cpper as the cllectr metal in an xidizing atmsphere, the effects f Al, MgO, and additin n the disslutin behavir f rhdium in slags was examined Experimental Slag samples were prepared by melting the mixtures f reagent grade C, SiO, Al, MgO, and Cu O in a pure platinum crucible in air at 1573 K Experiments were carried ut by equilibrating 4 g f mlten slags, such as the, the MgO, and the systems, in a pure rhdium crucible (18 mm ID, 0 mm OD, 0 mm in depth) in an electrical resistance (SiC) furnace The schematic diagram f the experimental setup is shwn in Figure 1 When the slags was melted, the slight disslutin f cpper int slid rhdium was bserved In rder t determine the cntent f cpper in slid rhdium in equilibrium with the slags, a piece f rhdium sheet (thickness 15 μm, purity 999 %) was added int the slags The xygen partial pressure in the system was cntrlled by flwing dried air The gas flw rate was cntrlled at 100 ml/min Misture and CO in the dried air was remved by passing the gas thrugh silica gel, sda lime, and magnesium perchlrate, respectively The temperature was cntrlled within an accuracy f ±1 K using a prprtinalintegralderivative (PID) cntrller with a Pt/6%RhPt/30%Rh thermcuple After equilibratin, samples were remved frm the furnace and quenched at rm temperature by flushing Ar gas The slag cmpsitin in quenched samples and the cntent f cpper in slid rhdium equilibrated with the slag were determined by wet chemical analysis The cntent f rhdium, sdium, aluminum, magnesium, and cpper were determined by inductively cupled plasmaatmic emissin spectrmetry (ICPAES) The cntent f silicn in slags was determined by the gravimetric methd 3 Results and Discussin Experimental results f the disslutin f rhdium in slags were summarized in Table 1, and the cntent f cpper in slid rhdium equilibrated with the slag was summarized in Table 31 Equilibrium attainment Equilibratin time fr the disslutin f rhdium Figure 1 Schematic diagram f the experimental apparatus

3 C Wiraseranee et al / JMM 49 () B (013) Table 1 Experimental results f the disslutin f rhdium in slags ( O/SiO = 097) at 1473 K and = 01 atm 1 Sample N Slag cmpsitin/ mass pct Slubility f Rh / C X Time / h AlO 15 3 mass ppm O SiO Al R R Sample N Slag cmpsitin/ mass pct Slubility f Rh/ X MgO Time/ h 1 5 mass ppm O SiO MgO R Slag cmpsitin/ mass pct Slubility f Rh/ C Sample N X Cu Time/ h 15 mass ppm O SiO R nd nd nd nd nd nd nd: nt determined Table The cntent f cpper in slid rhdium in equilibrium with the slag at 1473 K and Sample N Slag cmpsitin/ mass pct O SiO X Cu in slag Time / h X Cu in ally p O p O C = 01 atm X Rh in ally int slags was firstly determined Accrding t the timedependence plt (Figure ), the slubility f rhdium in each slag system increased with time and became steady after 18 h In case f the slag, the disslutin f cpper frm the slags int slid rhdium was bserved Frm the measurement, the cntent f cpper in slid rhdium after 18 h was steady (Figure 3) Therefre, the equilibratin time fr the, the MgO, and the slag systems was assigned t be 18 h 3 The slubility f rhdium in Al, MgO and bearing slags The slubility f rhdium in the, the MgO, and the slags was measured at 1473 K and p O = 01 atm by varying the cntents f Al, MgO and in slags at a fixed O/SiO ml rati f 097 It was fund that

4 134 C Wiraseranee et al / JMM 49 () B (013) Figure Dependence f the slubility f rhdium in the, the MgO, and the slags ( O/SiO = 097) n experimental times at 1473 K in air ( p O = 01 atm) Figure 4 Dependence f the slubility f rhdium n the cntents f Al, MgO and in slags at a fixed O/SiO ml rati f 097 at 1473 K in air ( p O = 01 atm) Figure 3 Dependence f the cntent f cpper in slid rhdium equilibrated with the 38 O38SiO 4 slag (0 mass pct Cu) n experimental times at 1473 K in air ( p O = 01 atm) the slubility f rhdium drastically decreased when the cntents f Al and MgO in slags increased, but was fairly cnstant when the cntent f cpper in slags increased (Figure 4) In the bearing slags, the disslutin f cpper int slid rhdium was bserved The cntent f cpper in slid rhdium increased with increasing cntent f cpper in the slags (Figure 5) The disslutin f cpper int slid rhdium causes the decrease in the activity f slid rhdium frm unity Thus, the effect f additin n the disslutin f rhdium int slags cannt be Figure 5 Dependence f the cntent f cpper in the Cu Rh allys n the cntent f cpper in the O SiO slags in air ( p O = 01 atm) at 1473 K determined slely by the dependence f the slubility f rhdium n the cntent f in slags Cnsequently, the cmparisn f the effect f xide additin n the disslutin f rhdium int slags was made by using the activity cefficient f rhdium and rhdate capacity in slags as discussed in the fllwing sectins 33 The activity cefficient f 15 in Al, MgO and bearing slags The activity cefficient f rhdium in slags were determined by cnsidering that rhdium disslved int slags as 15 (Eq (1)) as prpsed in the

5 C Wiraseranee et al / JMM 49 () B (013) previus study [5] The activity cefficient f 15 in slags was calculated by the fllwing equatins, referring t pure slid 15 as a standard state Rh s 3/4O (1) g 15 s G f, Rh O T J / ml 15 () X Gf, RTln (3) / RhXRh po The activity f slid rhdium in equilibrium with the Na G Al 8 and the MgO slags was assigned t unity Meanwhile, because cpper in the slag slightly disslved int slid rhdium, it was assumed that rhdium in the RhCu slid allys beys Rault s law Hence, the activity f slid rhdium in equilibrium with the slag was assigned t the cntent f rhdium in the slid allys Dependence f the activity cefficient f 15 n the cntents f Al, MgO, and in slags was determined in Figure 6 decreased with increasing cntent f Al [10] The activity f O in the slags at 1400 K reprted in the previus study was determined by referring t the 40(ml pct) O60SiO melt The activity f O in the slags which is used fr the discussin in this study was recalculated by changing the standard state t pure liquid O Frm Figure 7, the disslutin f rhdium int slags as an acidic xide was supprted by the increasing trend f the slubility f rhdium when the activity f O in the slags increased Figure 7 Dependence f the slubility f rhdium in the slags at 1473 K n the activity f O Figure 6 Dependence f the activity cefficient f 15 n the cntents f (u) Al, (p) MgO, and (l) at a fixed O/SiO ml rati f 097 at 1473 K and p O = 01 atm The activity cefficient f 15 slightly decreased with increasing cntent f Cnsidering that 15 behaves as an acidic xide in the melts [5], it is deduced that behaved as a basic xide and enhanced the disslutin f rhdium int the slags It is generally knwn that Al is amphteric In this study, the drastic increment f the activity cefficient f 15 with increasing cntent f Al indicated that Al behaved as an acidic xide in the slags and suppressed the disslutin f rhdium Furthermre, it was reprted that, at a fixed O/SiO rati f 1, the activity f O in the slags at 1400 K drastically In case f the effect f MgO additin, the activity cefficient f 15 gradually increased with increasing cntent f MgO Since MgO is cmmnly cnsidered as a weak basic xide, especially when cmpared t O, it was suggested that at a fixed O/SiO rati f 1, MgO in the MgO slags behaved as a diluent f the slag basicity and suppressed the disslutin f rhdium in the slags The ptical basicity, prpsed by Duffy and Ingram [11], is defined as the pwer f an xide t dnate a negative charge Table 3 shws ptical basicity (Λ) f varius xides Table 3 Optical basicity f varius xides Pure xides Optical basicity, Λ Ref O 115 [1] CaO 100 [1] MgO 078 [1] Al 06 [1] SiO 048 [1] Cu O 097 [13] CuO 090 [14]

6 136 C Wiraseranee et al / JMM 49 () B (013) By the use f the calculated ptical basicity (Λ th ), the effect f the change in slag basicity due t the additin f Al, MgO, and n the activity cefficient f 15 in slags was determined (Figure 8) It is nted that the crrectin n the calculated ptical basicity f the slag was made cnsidering the charge cmpensatin; namely the fact that Na + was cnsumed fr the charge 5 balancing in AlO 4 tetrahedral [15] Additinally, the ptical basicity f the slags was calculated by cnsidering the slags as the Cu OCuO quaternary system The cntent f Cu O and CuO in the slags was calculated by assuming that the ml rati f Cu + /Cu + in the sdium metasilicate was 11 [16] t pure slid CuO 05 and pure slid CuO as standard states, respectively) culd be determined frm the fllwing equatins Cu(s)+1/4O (4) (g)=cuo 05(s) T ( J / ml) [9] (5) G f, CuO 05 G CuO05 f, CuO RTln 05 (s) 14 / Cu XCu po Cu(s)+1/O (g)=cuo(s) G T ( J/ml) G f, CuO 05 RT ln CuO f, CuO 05 (s) / CuXCu p 1 O (6) (7) [9] (8) (9) The activity f CuO 05 in the slags measured 3 in air ( p O = 01 atm) cnsiderably decreased R frm that in the Cu O slags in equilibrium with liquid cpper measured at 1573 K in the Ar atmsphere (Figure 9) [18] Figure 8 Dependence f the activity cefficient f 15 n the calculated ptical basicity at 1473 K and p O = 01 atm The activity cefficient f 15 in the O SiO and the MgO slags sharply increased with decreasing ptical basicity after the additin f Al and MgO, indicating that Al and MgO suppressed the disslutin f rhdium in slags Meanwhile, the ptical basicity f the slags increased with increasing cntent f in the slags, suggesting that the decrease in the activity cefficient f 15 in the slags was resulted frm the increase in the slag basicity by the additin f 34 The activities f CuO 05 and CuO in the slags The activity f cpper in slid rhdium (referred t pure slid cpper as a standard state) in equilibrium with the slag was derived frm the cntent f cpper in slid rhdium and the activitiescmpsitins relatin in the CuRh system at 1473 K [17] Thus, the activities f CuO 05 and CuO (referred Figure 9Dependence f the activities f CuO 05 and CuO in the slag at 1473 K ( p O = 01 atm), and the activity CuO 05 f in the Cu O slag at 1573 K in equilibrium with liquid cpper, n the cntent f cpper in slags at the O/SiO rati f 097 CuO 05 in the Cu O slags exhibited the psitive deviatin frm ideality [18], whereas that in the slags was likely t exhibit the Raultian behavir Meanwhile, CuO in the O SiO Cu O slags exhibited the slight negative deviatin frm ideality It was hypthesized that the existence f CuO in the slags results in the decrease in the activity f CuO 05 in the slags 35 Rhdate capacity f Al, MgO and bearing slags C Rhdate capacity f slags ( ) is defined as the capacity f a rhdate in ( ) in slags [5] It was

7 C Wiraseranee et al / JMM 49 () B (013) prpsed by referring that rhdium disslved int slags in the frm f a rhdate in by the fllwing reactin 3 1 Rh(s) + O (g)+ O (in slag) = 4 = (in slag) [5] (10) Rhdate capacity f a slag system at a particular temperature is determined frm the slubility f rhdium in slags, the activity f rhdium, and xygen partial pressure as fllws 1 ( mass pct in slag) ( a ) / O C K (11) 34 / ( 10) ( arh )( po ) f Frm Eq (8), K (10) is the equilibrium cnstant f O Eq (10), a is the activity f xide in (O O ) in slags, and f is the activity cefficient f the rhdate in in slags As 4a basicity index f slags, the ptical basicity was emplyed t investigate the relatinship between slag basicity and rhdate capacity f slags Figure 10 illustrates the relatinship between rhdate capacity in the, the MgO, and the slags and the calculated ptical basicity pssible rhdate capacity f varius slag systems, the use f the crrelatin between the rhdate capacity and the calculated ptical basicity was prpsed 4 Cnclusins With the aim t minimize the rhdium lss int slags in the recvery f rhdium in an xidizing atmsphere, the effects f Al, MgO, and additin n the disslutin behavir f rhdium in the p O slags in air ( = 01 atm) at 1473 K was investigated The fllwing findings were revealed At a fixed O/SiO rati f 097, the slubility f rhdium sharply increased with increasing cntents f Al and MgO in slags, but rather maintained cnstant with increasing cntent f Cpper in the slag was fund t disslve int slid rhdium and decreased the activity f slid rhdium in the system Al behaved as acidic substance in slags and drastically suppress the disslutin f rhdium Since MgO is less basic than O, it behaved as a diluent f slag basicity, resulted in the increment f the activity cefficient f 15 when the cntent f MgO increased The activity cefficient f 15 in the bearing slags decreased with increasing cntent f ; therefre, it was deduced that cpper xides behaved as basic substances and enhanced the disslutin f rhdium int slags Rhdate capacity was fund t increase with increasing ptical basicity f slags The linear relatinship was fund t be the bestfit crrelatin between rhdate capacity and the calculated ptical basicity The crrelatin prvides a pssibility fr the estimatin f rhdate capacity in the multicmpnents recycling slag Acknwledgement Figure 10 The crrelatin between rhdate capacity and the calculated ptical basicity Rhdate capacity f slags increased with increasing ptical basicity in all slag systems The best fit f the crrelatin was fund t be a linear relatinship in Eq (1) It is nted that the ptical basicity f the and the slags was calculated by the apprach which described in the sectin 33 lg C (1) th, crr 414 In the recvery f rhdium in an xidizing atmsphere, p it is expected that the recycling slag cntains varius xide cmpnents where thermdynamic prperties f rhdium in thse slag systems are nt clarified In rder t estimate the This research was supprted by the New Energy and Industrial Technlgy Develpment Organizatin (NEDO), Japan The authrs wuld like t thank Mr Yuzuru Nakamura, Dwa Metals & Mining C, Ltd, Japan, fr the fruitful advices and discussins References [1] J Butler, Platinum 01, Jhnsn Matthey Plc, Hertfrdshire, 01 [] M Bensn, CR Bennett, JE Harry, MK Patel, and M Crss, Resur, Cnserv Recycl, 31 (000) 1 7 [3] C Hagelüken, Wrld MetallErzmet, 59 (006) [4] TH Okabe, H Nakada, and K Mrita, J Surf Sci Sc Jpn, 9 (10) (008) (in Japanese with English abstract) [5] C Wiraseranee, TH Okabe, and K Mrita, Metall

8 138 C Wiraseranee et al / JMM 49 () B (013) Mater Trans, 44B (013) [6] S Nakamura and N San, Metall Mater Trans, 8B (1997) [7] H Shut, TH Okabe, and K Mrita, Mater Trans, 5 (10) (011) [8] K Yamaguchi, 4 nd Rare Metals Wrkshp, Octber 010, Tky, Japan, 010 (in Japanese) [9] I Barin, in Thermchemical Data f Pure Substances, VCH Verlagsgesellschaft, mbh, Weinheim, 1989 [10] H Ith and T Ykkawa, Trans Jpn Inst Met, 5 (1) (1984) [11] JA Duffy and MD Ingram, J NnCryst Slids, 1 (1976) [1] JA Duffy, Gechim Csmchim Acta, 57 (1993) [13] E BrdesRichard and P Curtine, in Metal Oxides: Chemistry and Applicatins (JLG Fierr Editr), CRC Press, Bca Ratn, FL, 006, p 36 [14] KC Mills, in Slag Atlas, nd ed (Verein Deutscher Eisenhüttenleute Editr), Verlag Stahleisen GmbH, Düsseldrf, 1995, p 11 [15] KC Mills, ISIJ Int, 33 (1) (1993) [16] S Nakamura and N San, Metall Mater Trans, B (1991) [17] C Wiraseranee, Thermdynamics f Rhdium and Platinum in Mlten Slag, The University f Tky, 01 (Dctral thesis) [18] Y Takeda, G Rivers, Y Park, and A Yazawa, Trans Jpn Inst Met, 7 (8) (1986)