Kinetic and Mechanism of Ca Leaching in the Production of High-Purity Magnesia
摘要
To solve the adverse effects of calcium impurities in low-grade magnesite on the purity and properties of the prepared magnesium oxide, the article proposed to use magnesium chloride as a calcium remover to remove calcium impurities from magnesite by a wet process. We found that under the condition of MgCl2 concentration of 0.2 g/mL, leaching temperature of 343 K, and liquid-to-solid ratio of 12 mL/g, the calcium leaching rate could reach 97.02% for 80 min, and the purity of MgO of 99.02% was obtained, which met the purity requirement of high-purity magnesium oxide (ωMgO > 98%). The leaching kinetics of calcium from post-forging magnesite powder (PMP) were analyzed using the homogeneous phase model and heterogeneous reaction model. The calcium leaching process from PMP can be categorized into two distinct stages. The first stage was controlled by chemical reaction, which was in line with the second-order rate model of the homogeneous model, and the second stage was controlled by the synergistic control of product layer diffusion and chemical reaction. The apparent activation energy required in the first stage (10.883 kJ/mol) was lower than that in the second stage (22.215 kJ/mol) because of the presence of the product layer.