Effect of Slag Composition on the Distribution Behavior of Pb between Fe t O-SiO 2 (-CaO, Al 2 O 3 ) Slag and Molten Cop
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INTRODUCTION
IT is very important in copper smelting and refining processes to remove several minor elements such as Pb, Bi, Sb, As, and Te.[1,2] Specifically, Pb is a troublesome impurity that increases the amount of slime in the electrorefining process. Also, from the viewpoint of copper smelting and refining processes, Pb is a detrimental element that is always present in sulfide concentrates and must be eliminated. Therefore, the content of Pb in molten copper should be lowered within an appropriate concentration range during plant operation; thus, we need specific knowledge of the effect of slag composition on the thermodynamic behavior of Pb in molten slag. Kim and Sohn[3] examined the effects of CaO, Al2O3, and MgO additions on the distribution behavior of Pb between an iron silicate slag and liquid copper under a pO2 ¼ 1012 106 atm at CO-CO2 atmosphere 1523 K (1250 C), and they found that the distribution ratio of Pb and the activity coefficient of PbO were not
JUNG HO HEO, Graduate Student, and JOO HYUN PARK, Professor, are with the School of Materials Science and Engineering, University of Ulsan, Ulsan 680-749, Korea. Contact e-mail: [email protected] SOO-SANG PARK, Research Engineer, is with the Metals and Materials Research Department, LS-Nikko Copper, Ulsan 70, Korea. Manuscript submitted January 1, 2012. Article published online August 7, 2012. 1098—VOLUME 43B, OCTOBER 2012
significantly affected by the additives. The governing factors affecting Pb solubility in iron silicate slag were proposed as the oxygen potential ðpO2 Þ and the ratio of FetO/SiO2 (or SiO2 content). Matsuzaki et al.[4] calculated the activity coefficient of PbO (cPbO) with the regular solution model and plotted the iso-cPbO contours for the CaO-SiO2-Al2O3 ternary slag at 1623 K (1350 C). The value of cPbO decreased as CaO was replaced with SiO2 at any fixed concentration of Al2O3, indicating the basic character of PbO in the slag. A similar tendency of the effect of CaO/SiO2 ratio on the cPbO was also reported by Kudo et al.[5] using the FetO-CaO-SiO2 system in equilibrium with metallic iron at 1573 K (1300 C). In that study,[5] the changes in temperature from 1473 K to 1573 K (1200 C to 1300 C) did not have a significant effect on cPbO in the slag. Decterov and Pelton[6] computed the distribution behavior of Pb among matte, slag, and liquid copper at 1523 K (1250 C) and pO2 ¼ 1012 105 atm under conditions from silica saturation to magnetite saturation. The distribution ratio of Pb decreased with increasing Fe/SiO2 ratio from silica to magnetite saturation. The small addition of CaO (3 mass pct) also decreased the Pb distribution ratio. Kashima et al.[7] observed that Pb was distributed among crude copper, white metal, and silica-saturated iron silicate slag in rather similar concentrations at 1573 K (1300 C) under controlled SO2 partial pressure. Furthermore, Acuna and Yazawa[8] found that the Pb distribution ratio was in the order of iron silicate > barium ferrite ‡ calcium ferrite slag when the copper content in the
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