Rapid and efficient recovery of molybdenum from spent mandrel dissolving acid solution

The method of quickly and efficiently recovering molybdenum from a mixed sulfuric acid-nitric acid aqueous solution having substantial quantities of molybdenum dissolved therein, said mixed acid solution having been used to dissolve molybdenum mandrels from coiled tungsten filaments, which method comprises:

• diluting said mixed acid solution with water to a predetermined acid-water volume ratio, adding anhydrous ammonia to said diluted solution at a predetermined rate with the predetermined acid-water ratio of said diluted solution and the predetermined rate of anhydrous ammonia addition thereto causing the solution temperature to rise to at least about 90.degree. C., maintaining the solution temperature at less than its boiling temperature, and continuing the controlled anhydrous ammonia addition to said solution until the solution pH is from about 1.5 to about 3.5;
• seeding the partially neutralized solution with a small predetermined amount of ammonium molybdate solid particles;
• maintaining the seeded and heated solution at a temperature of at least about 90.degree. C. but less than the solution boiling temperature for a period of from about one hour to about four hours to precipitate substantially all molybdenum therefrom as ammonium molybdate;
• and
• separating the resulting precipitated ammonium molybdate from the residual solution.