THERMODYNAMICS OF As, Sb AND Bi DISTRIBUTION DURING REVERB FURNACE SMELTING

Transcription

1 Journl of Mining nd Metllurgy, 38 (1 2) B (2002) THERMODYNAMICS OF As, Sb AND Bi DISTRIBUTION DURING REVERB FURNACE SMELTING N.Mitevsk* *RTB BOR, Copper Institute, Bor, Yugoslvi **University of Belgrde, Technicl fculty Bor, Bor, Yugoslvi (Recived 23 Decembr 2001; ccepted 20 April 2002) Abstrct The results of thermodynmic nlysis of rsenic, ntimony nd bismuth distribution between copper mtte nd discrd slg in reverbertory smelting t 1573 K re shown in this pper. On the bsis of chemicl nlysis of the melt smples tken during stble opertion of the reverb furnce No.2 in the Copper Smelter nd Refinery, RTB Bor (Yugoslvi), the distribution coefficients of As, Sb, nd Bi between copper mtte nd slg re clculted. The influence of the mtte grde on the minor element distribution coefficients between copper mtte nd slg is lso nlyzed, s well s rsenic, ntimony nd bismuth distribution in slg. Keywords: thermodynmics, smelting, distribution, rsenic, ntimony, bismuth 1. Introduction Sulfide copper ores contin minor elements such s Au, Ag (noble metls); Co, Ni, Pt, Pd (Group VIII); Zn, Cd, Hg (Group II-B); Sn, Pb (Group IV-A); Mo (Group VI-B); Bi, Sb, As (Group V-A); Se, Te (chlcogens); nd Cl (hlogen). J. Min. Met. 38 (1 2) B (2002) 93

2 N. Mitevsk It is very importnt to determine the behvior of minor elements in regrd to their effects on the qulity of the copper produced s well s their impct on economicl nd environmentl fctors. Minor elements trnsition from copper mtte into slg cn be consider s impurity elimintion or vluble component losses into slg [1]. Arsenic forms Cu 3 As prticles in nneled copper nd cn reduce the electricl conductivity of the metl by 23% t rsenic content of only 0.1 wt.%. Bismuth in copper t concentrtion of wt.% renders the host metl brittle, nd both ntimony nd rsenic rise the recrystlliztion temperture of copper. So, their concentrtion must be limited in the finl product to ensure its commercil vibility. Becuse of tht, it is essentil to elucidte the thermodynmic nture of As, Sb, nd Bi in order to estblish effective wys of eliminting these impurities during smelting. 2. Industril Investigtion The industril investigtion of rsenic, ntimony nd bismuth distribution between copper mtte nd slg long the furnce length is done by deep sonding of the melt from the reverbertory furnce No.2 seling in the Copper Smelter nd Refinery, RTB BOR (Yugoslvi) [2,3]. 3. Results nd Discussion 3.1. Minor Element Distribution between Copper Mtte nd Slg In times pst ll metls present in fylite slg re consider to be in oxidic form, becuse slg is mixture of oxides simply presented by FeO-Fe 2 O 3 -SiO 2 system [4]. But this stnds only for Co, Ni, Pb, Sn, Zn. Investigtions [5,6] showed tht behvior of other elements in slg is different. Depending on nture of the element nd operting conditions, the following mechnisms of chemicl dissolution elements in fylite slg cn be considered [1]: - Oxidic dissolution: Co, Cu, Ni, Pb, Zn; 94 J. Min. Met. 38 (1 2) B (2002)

3 Thermodinmics of As, Sb nd Bi distribution... - Sulfidic dissolution: Co, Cu, Ni, Pb; - Monotomic dissolution: Ag, As, Au, Bi, Sb, Se, Te; - Moleculr dissolution: S, Se, Te; - Hlidic dissolution: Ag, Au, Cu, Pt. The first three dissolution mechnisms cn be confirmed by nlysis of sulfur nd oxygen prtil pressures digrm t 1573K which presents the stbility of metl, sulfide nd oxide of ech element, with presumption tht Me = MeS = MeO, Fig. (1). Figure 1. Sulfur-oxygen potentil for metl-sulfur-oxygen systems t 1573K J. Min. Met. 38 (1 2) B (2002) 95

4 N. Mitevsk Sulfides nd oxides of zinc, coblt, nickel, led nd copper re stble in smelting conditions, so these elements re present in melt in both forms. On the other side, ntimony, rsenic, bismuth nd silver re stble in metllic form. Clculted distribution coefficients of rsenic, ntimony nd bismuth re shown in Fig. (2). Copper hs the highest distribution coefficient, whose concentrtion in the Figure 2. Minor element distribution coefficients copper mtte is 86 times higher thn in the slg. The trnsition of bismuth into the mtte is lmost complete (L>>1). Arsenic hs distribution coefficient little bove one; its concentrtion is higher in copper mtte. But, becuse of the fct tht the slg mss is round 70% of totl furnce melt mss, bigger mount of rsenic is in the slg. And finlly, distribution coefficient of 96 J. Min. Met. 38 (1 2) B (2002)

5 Thermodinmics of As, Sb nd... ntimony is less thn one, so it is concentrting in the slg. This confirms one of the most importnt technologicl functions of discrd slg - refining, for it dissolves unwnted elements from copper mtte. 3.2.Thermodynmic Considertion Thermodynmiclly, the distribution of metl Me between mtte nd slg cn be nlyzed on the bse of its ffinity to sulfur nd oxygen: MeS + FeO = MeO + FeS (1) K 1 = MeO MeS FeS FeO (2) Activities of FeS nd FeO in the copper mtte with verge copper content equl 0.4 [1], thus: K1 = MeO MeS = N N MeO MeS γ γ MeO MeS (3) where re: N MeO - mole frction of MeO in slg; N MeS - mole frction of MeS in copper mtte; γ - ctivity coefficient of MeO or MeS. Therefore, the distribution of metl cn be considered s rtio of mole frction of oxide in slg nd sulfide in copper mtte. The thermodynmic vlues for rsenic, ntimony nd bismuth distribution between slg nd mtte t 1573K is given in Tble 1. Clculted vlues for N MeO / N MeS show tht lmost ll mount of bismuth nd copper re trnsferred into copper mtte, while lmost ll mounts of rsenic nd ntimony re trnsferred into slg. On the bsis of Gibbs free energy vlues t 1573K (Tble 1) it cn be concluded tht the most stble oxides hve rsenic nd ntimony; this mens tht during the smelting process rsenic nd ntimony re oxidized nd J. Min. Met. 38 (1 2) B (2002) 97

6 N. Mitevsk Tble 1: Thermodynmic vlues for minor element distribution between slg nd mtte t 1573K ELEMENT (kj) K γ / γ MeO MeS NMeO / NMeS o G 1573 As Bi Cu Sb trnsferred to slg phse. This mechnism of trnsition into slg is directed by thermodynmic (melting point, boiling point, chemicl equilibrium, distribution coefficient, ctivity, ctivity coefficient, influence of prtil pressure of oxygen nd sulfur), kinetic (density, viscosity, gs nd liquid flow, diffusion coefficient) nd process (temperture, slg composition, furnce construction) prmeters [7]. On the other side, sulfides of rsenic, ntimony nd bismuth hve high vpor pressure (>>1, nd tm, respectively). It is very hrd to remove them by oxidtion ( G o 1573 > 0) nd introduce them into the slg, so they evporte in sulfidic form [8]. Besides, the direct reduction of sulfide to metl vpor is chrcteristic for ntimony nd bismuth. The mechnism of evportion depends on similr prmeters s mechnism of trnsition into the slg [7] Mtte Composition Influence on Minor Element Distribution The influence of copper content in the mtte on rsenic, ntimony nd bismuth distribution coefficients is shown in Fig.(3). The incresing of copper concentrtion in the mtte decrese the vlues of distribution coefficients of ll nlyzed minor elements. 98 J. Min. Met. 38 (1 2) B (2002)

7 Thermodinmics of As, Sb nd Minor Element Distribution in Slg The results of investigtion of minor element distribution in the slg phse long the slg melt depth nd the furnce length re shown in Tble 2 nd Figure 4. The concentrtion of rsenic, ntimony nd bismuth decrese from SL3 to SL6. As mentioned before, sulfides of these elements, s well s Figure 3. Minor element distribution coefficients vs. copper mtte composition metllic ntimony nd bismuth, hve high vpor pressures, so they trverse to gs phse which lowers their concentrtion in the slg. 4. Conclusion On the bsis of chemicl nlysis of the smples tken during stble opertion of the reverb furnce No.2 in Copper Smelter nd Refinery, RTB Bor (Yugoslvi), the distribution coefficients of rsenic, ntimony nd J. Min. Met. 38 (1 2) B (2002) 99

8 N. Mitevsk Tble 2. Minor element content in slg long slg depth nd furnce length SAMPLE ELEMENT As Bi Sb I SL3 II III IV I SL4 II III IV I SL5 II III IV I SL6 II III IV bismuth between copper mtte nd slg re determined. The trnsition of bismuth into the mtte is lmost complete (L>>1). Arsenic hs distribution coefficient little bove one. And finlly, distribution coefficient of ntimony is less thn one, so it is concentrting in the slg. 100 J. Min. Met. 38 (1 2) B (2002)

9 Thermodinmics of As, Sb nd... Figure 4. Minor element distribution in the slg phse J. Min. Met. 38 (1 2) B (2002) 101

10 N. Mitevsk The influence of the mtte grde on the minor element distribution coefficients is lso nlyzed. The incresing of copper concentrtion in the mtte decrese the vlues of distribution coefficients of ll nlyzed minor elements. The distribution of these elements in the slg phse is determined, too. The concentrtion of rsenic, ntimony nd bismuth decrese from SL3 to SL6. Their sulfides, s well s metllic ntimony nd bismuth hve high vpor pressures, so they trverse to gs phse, which lowers their concentrtion in the slg. Acknowledgements The uthors wish to thnk the RTB Bor (Yugoslvi), Copper Institute nd Copper Smelter nd Refinery, for support of this investigtion. The contribution of Petr Šukletovi}, Sš Rdulovi} nd Sš Ivnovi} re grtefully cknowledged. References 1. M.Ngmori, P.J.Mckey, Met.Trns., 9B (1978) N.Mitevsk, Doctorl thesis, University of Belgrde, 2000, p.82. (in Serbin) 3. N.Mitevsk et l., JMM, 3-4 (2000) A.Yzw, Cn.Met.Qurt., 13 (3) (1974) M.Ngmori, P.J.Mckey, P.Trssoff, Met.Trns., 6B (1975) M.Ngmori, P.J.Mckey, Met.Trns., 8B (1977) P.J.Mckey, Cn.Met.Qurt., 21 (3) (1982) M.Devi, A.Lurschi, COPPER 91 Interntionl Symposium, August, Ottw (Cnd), 1991, p J. Min. Met. 38 (1 2) B (2002)