Synthesis of alumina based on industrial waste material

Abstract

A hazardous waste generated in slag milling process by the aluminium industry was used as a raw material for the synthesis of alumina, α-Al2O3. This waste is considered as hazardous material in the European legislation due to the release of toxic gases (hydrogen, ammonia, methane and hydrogen sulphide) in the presence of water. The process developed in this work allows to obtaining 1 ton of alumina from 4 tons of hazardous waste and generates an inert solid residue consisting principally of spinel, corundum and quartz with possible uses in cements or glass industry. This process consisted of two steps: in the first one, nearly 90% of aluminium present in the waste is recovered as a nanocrystalline boehmite, γ-AlOOH by hydrothermal treatment of the waste. In the second step, the alumina is obtained by calcination of the boehmite at 1400ºC in air. The chemical composition of the alumina obtained consisted of 95% Al2O3, 3.3% Fe2O3, 0.8% SiO2 and other minor oxides to balance.