Method of recovering molybdenum oxide

A method of producing molybdenum oxide which comprises the steps of:

• (a) forming an aqueous suspension of a molybdenum sulfide impurity-containing concentrate having a particle size of substantially 70 microns;
• (b) subjecting the suspension produced in step (a) to an elevated oxygen partial pressure and an elevated temperature in an autoclave to oxidize the molybdenum sulfide to molybdenum oxide and produce another suspension, and maintaining the suspension density during oxidation within a range between 100 and 150 g of solids per liter;
• (c) filtering said other suspension to recover molybdenum oxide therefrom and produce a first filtrate containing sulfuric acid;
• (d) neutralizing said first filtrate at least partially by adding lime or limestone thereto to produce a third suspension containing calcium sulfate;
• (e) filtering said third suspension to recover calcium sulfate and produce a second filtrate;
• (f) recirculating said second filtrate to step (a) as the sole recirculated liquid and at a rate sufficient to maintain the suspension density of the suspension entering step (b) between substantially 100 and 150 g of solids per liter;
• and
• (g) controlling the temperature in said autoclave to maintain it between 230.degree. C. and 245.degree. C. and maintaining the pressure in said autoclave by varying said suspension density within said range.