Recovery of Molybdenum from Sulfide Concentrate by Electro-Oxidation and Precipitation.

Abstract

Leaching of molybdenum concentrate in NaCl aqueous solutions by electro-oxidation has been investigated, and the major process parameters, such as current density, temperature, and pulp density (nominal content of the concentrate in slurry) have been experimentally examined. The leaching rate of the concentrate was found to be proportional to current density, while the molybdenum concentration in the leach solution increased linearly with time. These results show that the concentrate was effectively oxidized by oxidizers produced by electrolysis of the NaCl solution, then dissolved rapidly into the solution. Increase in pulp density results in preferential oxidation of iron and copper in the concentrate, and it reduces the efficiency of molybdenum extraction. With the purpose of examining the feasibility of molybdenum recovery through solubility change, the pH dependence of molybdenum solubility in 10 mass% NaCl solution was investigated at various temperatures between 298 and 353 K. The solubility of molybdenum was found to be lower than 0.05 mol/l in the range of pH from 2 to 3, and increased with increasing temperature and pH of the solution. Precipitation experiments from leach solution were then examined by changing pH of the solution, and solid MoO3·(H2O)x crystals, free of sulfur, were obtained from the leach solution containing large amount of SO42-. Trace rhenium in the concentrate was found dissolve into the leach solution and co-precipitate with molybdenum during this process.