Study on the effect of Si and silicide on leaching Al2O3 from magnesium smelting reduction slag

Abstract

The main phases of the reduction slag from magnesium production by vacuum aluminothermic reduction using dolomite and magnesite as materials and using Al-Si alloy as reductant are CaO · 2Al2O3 and 2CaO · SiO2. It also has amount of unreacted Si. The Al2O3 content of reduction slag is about 55% and SiO2 is about 10%. When leaching Al2O3 with a mixture solution of sodium hydroxide and sodium carbonate, Si and SiO2 would enter into leaching solution and has a negative effect on Al2O3 leaching. The effect of Si and silicide on leaching Al2O3 from magnesium smelting reduction slag was studied in laboratory. The results show that total Si and partial SiO2 would enter into leaching solution and react with NaAl(OH)4 to form (Na2O · Al2O3 · SiO2)6 · 27H2O which is present in leaching residue and makes a loss of Al2O3.