Dissolution kinetics of molybdite in KOH media at different temperatures

The dissolution kinetics of synthetic molybdite (MoO3) in a potassium hydroxide (KOH) medium was studied by varying the system temperature, KOH concentration, and particle size. Additionally, the effects of the stirring rate and different reagents such as barium hydroxide (Ba(OH)2), calcium hydroxide (Ca(OH)2), and sodium hydroxide (NaOH) were also evaluated. The experiments were performed in a reactor with controlled temperature and agitation. The results indicated that the dissolution reaction mechanism of molybdite generates potassium molybdate (K2MoO4) without intermediate compounds. Temperature (6-80 °C), KOH concentration (0.0005-0.025 mol/L), and particle size (5-40 μm) positively affected the dissolution of molybdite. The maximum Mo recovery was 67.5% in 0.25 h for 80 °C and 0.01 mol/L KOH. At the lowest temperature (6 °C), which is near the freezing point of water (0 °C), a substantial amount of Mo was recovered (17.8% in 45 min). The kinetics equation describing the molybdite dissolution in a KOH environment indicated that diffusion occurs through the porous layer. The activation energy was calculated to be 47.81 kJ/mol. A reaction order of 1.0 with respect to KOH concentration was obtained and was found to be inversely proportional to the squared particle size. The kinetics equation was obtained. The dissolution of molybdite resulting from the oxidation of a molybdenite concentrate (MoS2) led to a low molybdenum recovery, which was primarily caused by the consumption of KOH by impurities such as CaCO3 and Cr(MO4)3.