GB982098A - Improvements in production of alumina - Google Patents

Abstract

Substantially iron-free alumina is obtained from clay containing iron and aluminium by leaching the calcined clay with hydrochloric acid, converting iron in the leach liquor to a complex anionic ferric chloride [FeCl4-], contacting the liquor with a basic anion exchange polymer, thus separating iron from aluminium, and recovering alumina from aluminium chloride remaining in the liquor. In an example, clay is calcined at 1200 DEG F. for 1 1/2 hours, ground and leached by stirring with 20% w./w. aqueous HCl at a temperature of at least 160 DEG F. for one hour. Silica is separated and the solution containing chlorides of iron and aluminium is oxidized to an E.M.F. of 600 mV. at room temperature either electrically or using a suitable oxidizing agent. The solution is then contacted with a basic anion exchange polymer, which may be solid, e.g. a granular quaternary ammonium resin, or which may be liquid, e.g. a 0.1 molar solution of a secondary amine in kerosene containing an emulsion-preventing agent, e.g. n-decyl alcohol. In the latter case, mixer-settler extraction equipment may be used to effect contact. The iron-free aluminium chloride solution is evaporated and the residue is roasted in a kiln to give alumina, containing less than 0.05% Fe2O3 and less than 0.04% SiO2. Condensate from the evaporation stage and the roaster gases may be processed to obtain hydrochloric acid for re-use. Adsorbed complex ferric chloride anions may be eluted from the polymers with water or 0.5% w./w. aqueous HCl after entrained leach liquor has been displaced with 20% w./w. aqueous HCl. The eluate may be evaporated to give a concentrated ferric chloride solution or further processed for conversion of chloride to hydrochloric acid for re-use and for production of pure ferric oxide.