Optimizing rotary kiln operations for molybdenite concentrate oxidation roasting to produce molybdic trioxide

Abstract

The effects of the rotational speed (0–10 rpm) and temperature (550–650 °C) of rotary kiln drums on the oxidation roasting of molybdenite (MoS₂) concentrate was investigated in this study. Computational predictions indicated that production of MoO₂ was more favorable than that of MoO₃ up to a certain stage of the oxidation roasting process, after which MoO₃ is produced through the consumption of MoO₂. Thus, understanding the MoS₂–MoO₂–MoO₃ relationship and its equilibrium is important. A drum rotational speed > 5 rpm significantly increased the S reduction rate and considerably decreased the S content at 60 min to < approx. 5 %. Additionally, the S content at 60 min decreased with decreasing the temperature from 650 to 550 °C due to the MoS₂ concentrate exothermic reaction during oxidation roasting. The MoS₂ to Mo_xO_y (≈ MoO₂+MoO₃) conversion rate (%) was generally proportional to the rotational speed and reaction duration. X-ray diffraction analysis indicated that 5–10 rpm and 550–600 °C yielded a higher experimental conversion rate (97–98 %). Furthermore, the MoO₂ and MoO₃ conversions were separately quantified. Agglomeration was more pronounced without drum rotation and at higher temperatures. Analysis of the reaction kinetics using the unreacted-core model indicated that diffusion through the gas film layer is supported by the 20.9 kJ/mol activation energy obtained from the Arrhenius plot. Consequently, an appropriate drum rotational speed at a relatively low temperature is a prerequisite for producing MoO₃ through the oxidation roasting of MoS₂ concentrates in a rotary kiln.