Energy saving during alum production from kaolin with coproduction of alumina-silica composites from process silica wastes

Abstract

Egypt is among few countries producing aluminum sulphate alum for water purification from domestic kaolin (35% A12O3) as bauxite, the conventional raw material for alum production with 60% A12O3 is not available. The technologies applied are energy intensive require calcination prior to sulphuric acid leaching or direct leaching under high pressure and high temperature. In view of energy crises, direct leaching of kaolin with sulphuric acid in presence of fluosilicic acid disposed from phosphatic fertilizers industry was tried and the optimum conditions of producing drinking water alum were determined, thus the energy intensive calcination or pressure leaching steps could be canalled leading to improvement of production economics. Silica disposed after the leaching process is used to produce alumina- silica composites such as mullite 2 A12O3. 3 SiO2 through alkaline dissolution of silica and mixing of the produced sodium silicate with sodium aluminate produced from sodium carbonate thermal treatment with aluminum dross disposed from aluminum smelters. Controlled co-precipitation of the composite from mixture of the two solutions was achieved and X-ray investigation proved the formation of mullite phase. The Project has great impact on energy saving and economization of water treatment technology in addition to converting the industrial wastes to value added products—Waste to Wealth W2W.