Selective extraction of molybdenum and vanadium from spent catalysts by oxidative leaching with sodium aluminate and caustic

The process for treating an oily, spent hydrodesulfurization catalyst containing aluminum, at least one metal from the group consisting of molybdenum, vanadium and tungsten, at least one metal from the group consisting of nickel and cobalt, and sulfur which comprises forming an aqueous slurry by mixing said catalyst with an aqueous solution containing an amount of a base from the group consisting of sodium hydroxide and sodium aluminate stoichiometrically at least equivalent to convert in the presence of oxygen, the molybdenum, tungsten, vanadium and sulfur contents of said spent catalyst to sodium molybdate, sodium tungstate, sodium vanadate and sodium sulfate, oxygen pressure leaching the resulting slurry at a temperature of at least about 350.degree. F. for a time sufficient to oxidize to carbon dioxide substantially all the oil in said spent catalyst to oxidize to sodium sulfate substantially all the sulfur in said spent catalyst, and to dissolve molybdenum, tungsten and vanadium while producing a solid containing the aluminum, nickel and cobalt, discharging the products of said oxygen pressure leach at a pH not exceeding about pH 9 and separating the liquid containing said metal from the group consisting of molybdenum, tungsten, and vanadium and said sulfur but less than 100 ppm aluminum from said solid.