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

• Understanding the MoS 2 – MoO 2 – MoO 3 relationship and its equilibrium is important. • The MoO 3 conversion of 97–98 % was obtained at 5–10 rpm and 550–600 °C. • Agglomeration is more pronounced without drum rotation and at higher temperatures. • Optimal MoO 3 production requires appropriate drum rotational speeds and temperatures. The effects of the rotational speed (0–10 rpm) and temperature (550–650 °C) of rotary kiln drums on the oxidation roasting of molybdenite (MoS 2 ) concentrate was investigated in this study. Computational predictions indicated that production of MoO 2 was more favorable than that of MoO 3 up to a certain stage of the oxidation roasting process, after which MoO 3 is produced through the consumption of MoO 2 . Thus, understanding the MoS 2 –MoO 2 –MoO 3 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 MoS 2 concentrate exothermic reaction during oxidation roasting. The MoS 2 to Mo x O y (≈ MoO 2 +MoO 3 ) 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 MoO 2 and MoO 3 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 MoO 3 through the oxidation roasting of MoS 2 concentrates in a rotary kiln.