Leaching kinetics of calcium molybdate with hydrochloric acid in presence of phosphoric acid

Calcium molybdate (CaMoO4) is the main component of powellite and is a predominant intermediate in the pyrometallurgical and hydrometallurgical process of molybdenum. The extraction of Mo from CaMoO4 by a combination of phosphoric acid and hydrochloric acid was investigated. For further understanding of the leaching mechanism, the effects of five key factors were studied to describe the leaching kinetics. The results indicated that the dissolution rate of CaMoO4 was independent of the stirring speed. Mo extraction significantly increased with increasing HCl concentration and temperature, but decreased with increasing particle size. A shrinking core model with surface chemical reaction was found to withstand the dissolution of CaMoO4. The apparent activation energy was calculated to be 70.879 kJ/mol, and a semi-empirical equation was derived for the rate of reaction.