Reaction mechanisms of low-grade molybdenum concentrate during calcification roasting process

The effects of Ca-based additives on roasting properties of low-grade molybdenum concentrate were studied. The results show that calcium-based additives can react with molybdenum concentrate to form CaSO4 and CaMoO4. The initial oxidation temperature of MoS2 is 450 degrees C, while the formation of CaMoO4 and CaSO4 occurs above 500 degrees C. The whole calcification reactions are nearly completed between 600 and 650 degrees C. However, raising the temperature further helps for the formation of CaMoO4 but is disadvantageous to sulfur fixing rate and molybdenum retention rate. Calcification efficiency of Ca-based additives follows the order: Ca(OH)(2)>CaO>CaCO3. With increasing the dosage of Ca(OH)(2), the molybdenum retention rate and sulfur-fixing rate rise, but excessive dosages would consume more acid during leaching process. The appropriate mass ratio of Ca(OH)(2) to molybdenum concentrate is 1:1. When roasted at 650 degrees C for 90 min, the molybdenum retention rate and the sulfur-fixing rate of low-grade molybdenum concentrate reach 100% and 92.92%, respectively, and the dissolution rate of molybdenum achieves 99.12% with calcines being leached by sulphuric acid.