Kinetics of calcium molybdate leaching with sodium carbonate solution

Calcium molybdate CaMoO4 is the main product in the oxidative roasting of sulphide molybdenum concentrates and molybdenum raw materials with calcium-containing additives. After that, the cinder is processed hydrometallurgically. One of the main methods for extracting molybdenum from cinder is leaching with sodium carbonate solution. In order to determine the optimal parameters of Mo extraction, it is necessary to study the kinetics of CaMoO4 leaching with an aqueous solution of Na2CO3, to determine the dependences of the rate of the process of extracting molybdenum into solution on the main technological parameters: temperature, concentration of reagents, and to establish the limiting stage of the process. As starting materials, we used Reagent grade CaMoO4 and Na2CO3. The dissolution of CaMoO4 in Na2CO3 was studied within the concentration of soda СNa2CO3 = 100, 150, 200, 250, 300 g/dm3, in the temperature range from 20 to 90 °C, the ratio S : L = 1 : 2, 1 : 4, 1 : 6, 1 : 8, 1 : 10, duration from 30 to 300 minutes. The dependence of the CaMoO4 leaching rate on the mixing intensity has been studied. The apparent order of the reaction in the concentration range of Na2CO3 = 100…250 g/dm3 and the apparent activation energy in the temperature range from 60 to 90 °C have been determined. It was found that the optimal parameters of CaMoO4 leaching are: S : L = 1 : 6, T = 90 °C, СNa2CO3 = 200…250 g/dm3, stirring intensity is more than 500 min-1, with these parameters the process proceeds in a kinetic mode. It is shown, that at a Na2CO3 concentration of more than 250 g/dm3, the process proceeds with the formation of sodium-calcium carbonates; in this case, the limiting stage of the process is internal diffusion. In addition, the formation of sodium-calcium carbonates leads to an increase in the consumption of Na2CO3.