Enhancement of CaMoO4 calcine decomposition and recovery of calcium resource by HCl cycle leaching

The thermodynamic equilibrium diagrams of CaMoO4–CaSO4–H2SO4–H2O, CaMoO4–HCl–H2O and CaSO4–CaCl2–HCl–H2O systems at 298 K were established. The calculation results demonstrated that HCl displays a much higher solubility of CaSO4 than H2SO4. The leaching mechanism of Mo from CaMoO4 calcine was systematically investigated from the perspective of the micro particle properties variation. HCl exhibits an excellent leaching performance for Mo from CaMoO4 calcine due to the elimination of surface coating and the dissolution of a mass of Mo embedded in CaSO4 matrix. Excellent Mo leaching efficiency of 99.7% was achieved under the optimal conditions of decomposing CaMoO4 calcine by 2.4 mol/L HCl with a liquid/solid ratio of 10:1 at 50 °C for 60 min. Based on the experimental results, a highly efficient and green cycle leaching process of molybdenum from molybdenite was proposed, which eliminated surface coating and physical entraining, and converted most of the calcium from CaMoO4 calcine into high purity gypsum by-product.