Oxidation Mechanism of Molybdenite Concentrate

The oxidation mechanism of a commercial molybdenum concentrate was investigated up to 650 °C using thermal analysis. Upon introduction of air, the molybdenite concentrate started to lose mass due to the oxidation of MoS₂ to form molybdenum oxide and SO₂. After a rapid mass loss, this was followed by a period of mass gain due to the oxidation of MoO₂ to MoO₃. The solid-state reaction between MoS₂ and MoO₃ to form MoO₂ was also found to take place. Initially, as air is introduced, the rate is controlled by gas-phase diffusion of oxygen to the reaction surface. With time, as the surfaces of the MoS₂ particles become oxidized and the rates start to slow, MoO₃ starts to form. This generally leads to a mass gain as well as a slow down in oxidation rate due to the formation of a fairly dense MoO₃ product layer. The timing of the various reactions was very dependent on the actual experimental conditions such as sample mass, gas flow rate, and heating rates.