Mechanism and Kinetics of Stibnite Chloridizing with Calcium Chloride-Oxygen at 500 °C to 650 °C

Abstract

Copper concentrates with high levels of toxic impurity elements such as As, Sb Bi, must be pretreated before processing in the current smelting/converting refineries. The classical method for the pretreatment of dirty copper concentrates is partial oxidizing roasting, where the impurities are eliminated through the gas phase. However, volatilization of antimony and bismuth in conventional roasting processes using air or oxygen-deficient air is hardly achieved since antimony and bismuth remain in the calcine as non-volatile oxides. The chloridizing of stibnite with calcium chloride was studied as an alternative to volatilize antimony from impure copper concentrates because the vapor pressure of antimony chloride is higher than the vapor pressures of antimony oxide or sulfide at low temperatures. Thus, in the present work, the kinetic study of chloridizing of antimony from stibnite using calcium chloride as the chloridizing agent was studied at roasting temperatures 500 °C to 650 °C. The salient aspects determined in this study are that the chloridizing of stibnite starts with the formation of Sb₂O₃ followed by the chloridizing of this oxide by chlorine gas. The formation of antimony oxide Sb₆O₁₃ deters the complete elimination of antimony from stibnite. By using the unreacted shrinking core model 1 − (1 − α)^1/3 = k_rt, the chloridizing rate of stibnite with CaCl₂ and oxygen was found to be of 0.6 order with respect to the oxygen partial pressure, and the calculated energy of activation is 62 kJ mol⁻¹ in the range from 500 °C to 650 °C.