Preparation of sodium molybdate from molybdenum concentrate by microwave roasting and alkali leaching

The preparation process of sodium molybdate has the disadvantages of high energy consumption, low thermal efficiency, and high raw material requirement of molybdenum trioxide, in order to realize the green and efficient development of molybdenum concentrate resources, this paper proposes a new process for efficient recovery of molybdenum from molybdenum concentrate and preparation of sodium molybdate by microwave-enhanced roasting and alkali leaching. Thermodynamic analysis indicated the feasibility of oxidation roasting of molybdenum concentrate. The effects of roasting temperature, holding time, and power-to-mass ratio on the oxidation product and leaching product sodium molybdate (Na₂MoO₄·2H₂O) were investigated. Under the optimal process conditions: roasting temperature of 700°C, holding time of 110 min, and power-to-mass ratio of 110 W/g, the molybdenum state of existence was converted from MoS₂ to MoO₃. The process of preparing sodium molybdate by alkali leaching of molybdenum calcine was investigated, the optimal leaching conditions include a solution concentration of 2.5 mol/L, a liquid-to-solid ratio of 2 mL/g, a leaching temperature of 60°C, and leaching solution termination at pH 8. The optimum conditions result in a leaching rate of sodium molybdate of 96.24%. Meanwhile, the content of sodium molybdate reaches 94.08wt% after leaching and removing impurities. Iron and aluminum impurities can be effectively separated by adjusting the pH of the leaching solution with sodium carbonate solution. This research avoids the shortcomings of the traditional process and utilizes the advantages of microwave metallurgy to prepare high-quality sodium molybdate, which provides a new idea for the high-value utilization of molybdenum concentrate.