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UBC Theses and Dissertations

Reductive precipitation of molybdenum oxides for recovery of molybdenum from hypochlorite leach solutions Reid, Duncan Craig


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.

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