Recovery of chromium and magnesium from spent magnesia-chrome refractories by acid leaching combined with alkali precipitation and evaporation

In this study, recovery of chromium and magnesium from spent magnesia-chrome refractories was developed by acid leaching combined with alkali precipitation and evaporation. The optimized conditions for leaching were found to be particle size of -74 + 38 mu m, hydrochloric acid solution of 5.0 mol/L, liquid-solid ratio of 5:1, leaching temperature of 343 K, leaching time of 90 min and agitation speed of 400 rpm. Under these conditions, 95.14% Cr was remained in the residual in the form of chromite, which could be directly used for metallurgy. Subsequently, more than 90% Cu, Pb, Bi and Si can be removed from the leachate through adjusting the pH to 7.0 by magnesium hydroxide. Then, magnesium chloride hexahydrate can be obtained from the final solution by evaporation. Detection analyses showed that the production of chromite and magnesium chloride hexahydrate could be used as industrial raw material. What's more, kinetics of magnesium leaching was also studied, and the results revealed that leaching magnesium from the spent magnesia-chrome refractories was in accordance with pseudo-second-order model and the corresponding apparent activation energy was 68.75 kJ/mol.