Sulfate Ion → Molybdenum(4+) disulfate

Technical grade MoO3 was slurried in the leach solution so as to obtain a 2:1 weight ratio of leach to solids. Slurries were heated to 75°-85° C. and maintained at that temperature for two hours. The slurries were stirred vigorously during the digestion. The molybdenum oxide was separated from the leach solution by filtration. Percent of the molybdenum lost to the leach was determined. The molybdic oxide was then washed twice. Washing involved slurrying the oxide in 70°-80° C. water for 10 minutes and filtering to separate it from the wash. Percent of molybdenum lost to washes was determined. Efficiencies are tabulated in Table I. The better efficiency was obtained by the leach containing NH4NO3. The substitution of nitrate ion for sulfate ion is apparently responsible for the better efficiency. Presence of sulfate ion increases molybdenum solubility in acid solution by forming molybdenum sulfate complexes. When some of the sulfate ion is replaced with nitrate ion, molybdenum solubility decreases. Presence of additional nitrate ion increased oxidation of molybdenum IV to molybdenum VI, resulting in less molybdenum in the sludge after NH4OH digestion.