Abstract: A process for the recovery of molybdenum values from leach muds of molybdenite concentrates which have been roasted in air to convert molybdenum sulfide to molybdenum trioxide and subsequently leached with an aqueous alkaline solution for the recovery of soluble molybdenum salts. Leach mud is treated by the process of this invention by repulping the leach mud with aqueous ammonium hydroxide under pressure, at a temperature in the range of about 50 to 150.degree. C. for a period of 2 or more hours after which undissolved solid material is separated from the ammoniacal leach solution and repulped with an aqueous caustic leach solution at a temperature in the range of 50.degree. to 150.degree. C. for a period of 2 to 4 hours. Undissolved solid material is separated from the caustic leach solution and both the ammoniacal and the caustic leach solutions processed for the recovery of molybdenum salts therefrom.

Abstract: A process for recovering tungsten values in the form of ammonium paratungstate from tungsten ores and ore concentrates, particularly wolframite ores and ore concentrates, incorporating a plurality of steps for necessary removal of impurities and formation of the product ammonium paratungstate. The steps of the process include grinding, caustic leaching, filtrations, chemical treatment including acidification particularly for the removal of silica impurities, further filtration, solvent extraction of the tungsten values, stripping of the tungsten values from the solvent solution in the form of ammonium paratungstate, and recovery of the ammonium paratungstate product. The caustic leaching step may be carried out in the substantial absence of oxygen.