The effects of reductant and additive on the magnesium extraction from calcined dolomite via metallothermic reduction under vacuum condition

Abstract

The extraction of magnesium from calcined dolomite via vacuum metallothermic reduction process has been evaluated thermodynamically and investigated experimentally. The equilibrium phases formed during the metallothermic reduction as a function of pressure, reductant, temperature, and additive combination were thermodynamically analyzed. The experimental work consisted of calcination of dolomite – (Ca,Mg)CO3 and metallothermic reduction of the calcined dolomite/dolime – (Ca,Mg)O. The metallothermic reductions of the dolime with different reductants and additives were carried out in a laboratory scale vertical retort at a final holding temperature of 1200 °C and pressure lower than 10−4 atm using different reductant types (ferrosilicon or aluminum) and different additive combinations (CaF2 and B2O3). Magnesium metal was extracted from the dolime through metallothermic reduction by either ferrosilicon or aluminum. The residue from reduction with ferrosilicon disintegrated into fine powder, while the residue from reduction with aluminum remained as briquette. The physical degradation of the residue from reduction with ferrosilicon was found to be minimized by the B2O3 addition. The CaF2 addition increased the magnesium extraction, while the B2O3 addition decreased the magnesium extraction.