Effect of Microwave Roasting Pretreatment for Chromite on Its Oxidative Leaching Kinetics

To further improve the leaching behavior of chromite in the submolten salt medium of NaOH-H₂O, a microwave roasting pretreatment for chromite is proposed in the present work. Effects of the roasting pretreatment modes and reaction parameters on the leaching rate of Cr were systematically investigated. The results showed that the leaching rate of Cr from the chromite ore could be greatly boosted after microwave roasting. For chromite with microwave roasting pretreatment at 800 °C for 10 min followed by manual grinding, a Cr leaching rate of 98% was obtained within 120 min under the following reaction conditions: a reaction temperature of 240 °C, an oxygen pressure of 2.6 MPa, an NaOH-to-ore ratio of 4:1, a stirring speed of 800 rpm, and an NaOH concentration of 60 wt %. Moreover, kinetics analysis confirmed that the interface chemical reaction was the rate-determining step for the leaching of chromite. And the apparent activation energy of Cr extraction was calculated to be 26.7 kJ/mol, which was lower than that of 34.4 kJ/mol without microwave pretreatment. The enhanced leaching behavior of chromite with microwave roasting and subsequent grinding resulted from combined effects of the lattice distortion of spinel crystalline phases and refinement of mineral powder. Therefore, microwave roasting pretreatment has broad application prospects in improving the leaching kinetics of chromite by liquid-phase oxidation.