| abstract |
Disclosed is a process for recovering chromium, vanadium, molybdenum, and tungsten from secondary resources such as alloy scrap comprising a refractory metal and base metals such as cobalt, nickel, iron, and copper. The scrap is calcined with sodium carbonate in air to convert the refractory metal values to MoO4=, VO4=, WO4=, and CrO4= and the base metals to water insoluble oxides. A leach of the calcined materials produces a pregnant liquor rich in refractory metals which, after separation of the vanadium, molybdenum and tungsten values, is treated with CO, CHOO-CH3OH, or HCHO to reduce Cr+6 to CR+3. The carbonate and bicarbonate salts produced as a byproduct of the reduction are recycled to the calcination stage. As a result of the V, W, and Mo partition, a mixed solid comprising CaO.nV2O5, CaMoO4, and CaWO4 is produced. This is treated with carbonated water or formic acid to selectively dissolve vanadium values which are subsequently recovered by precipitation or extraction. The remaining mixed CaWO4 and CaMoO4 solid is treated with H2O2 and sulfuric acid to reject a Mo and W-free CaSO4 precipitate, and to produce a concentrated solution of tungsten and molybdenum. The W values are selectively precipitated from this solution by decomposing the peroxy complexes. The process has the advantages that a wide variety of different feed materials can be treated, no energy intensive pyrometallurgy is involved, reagent comsumption is minimized, and no aqueous effluents are produced. |