The Complex Chemical Treatment of Alumina–Silica-Containing Materials

Abstract

The results of a study of the complex treatment of alumina–silica-containing materials (fly ash, low-duality bauxites, clays, kaolins, nephelines) by chemical enrichment are presented. The de-siliconization of aluminum-containing raw materials with a high silica content is based on the property of hydroaluminum silicates (which are basic silica-containing minerals) to undergo intramolecular phase changes by thermal treatment, resulting in the formation of amorphous alkali-soluble silica. Dissolution of silica is effected by leaching the heat-treated raw material with sodium hydroxide solution, whereby the alumina remains in the solid state in the form of γ-Al₂O₃, or α-Al₂O₃. The use of chemical enrichment methods enables reduction of the silica content in the raw material and utilization of the resulting material for alumina production. The effectiveness of the chemical enrichment of alumina–silica-containing material depends in large measure on the possibility of the complete and economic utilization of all valuable components of the raw material. The possible methods of utilizing silica solutions for the production of valuable materials and methods of regenerating alkali from the silica solution are also considered.