A simple process to produce high purity MgO from leach liquor with high Mg/Ca mole ratio obtained by leaching calcined low grade magnesite in ammonium chloride solutions was developed on the basis of modeling the phase equilibria for the system NH4Cl-MgCl2-NH3-H2O with the Mixed Solvent Electrolyte (MSE) model embedded in the OLI platform. Leaching kinetics of calcined low grade magnesite in the ammonium chloride solutions were experimentally investigated. The optimum calcination temperature of low grade magnesite is 650 �C based onrding to the conversion ratio of magnesium and calcium.and solid-to-liquid ratio, on the leaching kinetics of magnesium and the conversion ratio of magnesium and calcium from the leaching experiments. The dissolution of calcined magnesite in NH4Cl was mainly controlled by the diffusion of the fluid through the inert solid layer adjacent to the surface of the unreacted core. An apparent activation energy of Mg extraction was 30.98 kJ/mol, which is a bit lower than that of Ca. In addition, an empirical kinetic model, in terms of most significant and observable variables which agree well with the conversion ratio of magnesium for the first stage of leaching process, was capable of predicting the effect of NH4Cl concentration, particle size of calcined magnesite, solid-to-liquid ratio on the conversion ratio of magnesium. Under the optimal leaching conditions, the leachate with high Mg/Ca mole ratio obtained was finally employed to the production of MgO with purity of 98.9% through the decomposition of intermediate 4MgCO3�Mg(OH)2�4H2O, and the new method was proved feasible.

Thermodynamics and kinetics studies of MgCl2-NH4Cl-NH3-H2O system for production of high purity MgO from calcined low grade magnesite

247th National Meeting (2014)

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