Kinetics of Precipitation of Low-Valent Tungsten and Molybdenum Oxides from Solutions by High-Pressure Hydrogen Reduction

摘要

Studies have been made on the kinetics of precipitation of low-valent tungsten and molybdenum oxides by high-pressure hydrogen reduction of ammonium molybdate and ammonium tungstate solutions, respectively. The production of low-valent oxides by the method has a number of advantages over conventional methods, particularly with regard to the higher recovery of metals from the solutions. Precipitation of low-valent tungsten and molybdenum oxides from ammonium tungstate and molybdate solutions by hydrogen reduction under high pressure and temperature with catalyst added is a complex heterogeneous catalytic reaction in which chemical reaction on solid surface may be considered principally as the reaction rate-controlling step. The reduction of blue tungsten oxide produced under low temperature will form Beta-W. By adding Si, Al and K as dopants into the blue oxide followed by two-stage hydrogen reduction, tungsten powder containing K atoms can be obtained.