Reductive precipitation of molybdenum oxides for recovery of molybdenum from hypochlorite leach solutions

The feasibility of reductive precipitation of molybdenum oxides as the molybdenum recovery stage of a hypochlorite leach of Cu-Mo rougher concentrates has been investigated. Hydrogen gas at elevated temperature and pressure and hydrazine at moderate temperature and atmospheric pressure were used as reductants. Reduction was performed on solutions containing 5 to 17 g/l Mo as sodium molybdate. Hydrogen reduction was successful only in the presence of a Pt catalyst, temperature = 200°C, pressure = 30 atm of H₂, and initial acidification to pH = 2. Ten hours was required to obtain 90% recovery of molybdenum as MoO₂. Reduction with hydrazine yielded an MoO(OH)₃ precipitate with 90% recovery obtained in 40 minutes at 50°C, pH = 4.5, and initial mole ratio of hydrazine to molybdenum of 4:1. Precipitation under the same conditions in the presence of 3 M NaCl gave only 70% recovery in 4 hours and the precipitate contained 3.3% sodium. The effect of NaCl is explained in terms of stabilization of mixed valent ionic molybdenum species in the presence of NaCl.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat