A Mineralogical Investigation of Sintering in Cu-Rich Polymetallic Concentrates During Roasting in Inert Atmosphere
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INTRODUCTION
CU-RICH polymetallic concentrates most commonly belong to the Cu-Fe-Pb-Zn-S system. They can additionally have elements such as Ag, Au, As, Sb and Bi in minor quantities. The Group 15 elements such as As and Sb are of concern as these impurity elements are difficult to remove in the conventional smelting-converting copper extraction process. The acceptable limits for these elements in the concentrates are generally very low (As < 0.2 wt pct, Sb-nil), and their concentrations above these limits may lead to smelter penalties.[1] Several experimental investigations have been performed aiming towards volatilization of impurity elements during roasting. Since As and Sb have tendencies to form non-volatile oxides at very low oxidation potential [As2O4(s) forms at pO2 ¼105.35 bar and Sb2O4(s) forms at pO2 ¼1010 bar, 700 C[2]], the gas atmosphere during these experiments is maintained at either low oxidation potential[3–6] or inert.[7–10]
PANDE NISHANT PRASAD, ANDREAS LENNARTSSON and CAISA SAMUELSSON are with Lulea˚ Tekniska Universitet, 97187 Lulea˚, Sweden. Contact e-mail: [email protected] Manuscript submitted November 2, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Removal efficiency of As has been found to be much better compared with that of Sb while roasting in inert conditions up to 700 C.[4,9,11] Haga et al.[11] reported that only above 700 C did the Sb volatilization in inert atmosphere improve appreciably and up to 90 pct removal could be achieved at 1200 C. However, the problem of incipient sintering of the calcines has been frequently reported[7,9,10] when the temperature of 700 C is approached while heating the polymetallic concentrates in inert atmosphere. Sintering is therefore a major problem to be resolved for a feasible volatilization of impurity elements during roasting. There have been limited studies related to sintering of concentrates during roasting. With some studies on zinc concentrates during oxidative roasting,[12–14] sintering has been only occasionally discussed for copper-rich concentrates,[10] lacking a detailed mineralogical investigation. Typical mineral phases in polymetallic sulphide concentrates include sulphides, sulphosalts[4,15–19] and metallic minerals lacking sulphur, e.g., silver antimonides.[16] A list of these minerals and their abbreviations referred to in this article are presented in Table I. Major minerals in the polymetallic concentrates are commonly chalcopyrite, sphalerite, galena and pyrite. In the context of mineral assemblage and metamorphism in sulphide ore deposits, high-temperature transformations in sulphide systems in inert atmosphere have been widely investigated. Kojima et al.[20,21] determined
Table I. Mineral Chalcopyrite Sphalerite Galena Pyrite Pyrrhotite Arsenopyrite Tetrahedrite Skinnerite Bournonite Meneghinite Gudmundite Dyscrasite
List of Mineral Abbreviations
Abbreviation
Stoichiometric Formula
Ccp Sph Gn Py Po Asy Ttr Skn Bour Mene Gud Dys
CuFeS2 (Zn,Fe)S PbS FeS2 Fe1-xS FeAsS (Cu,Ag,Fe,Zn)12(Sb,As)4S13 Cu3SbS
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