Acid process for the extraction of aluminium from argentine weathered basalts

Abstract

An acid process is proposed for the recovery of alumina of over 98.6% purity from aluminous red soils of Argentina. The dissolution variables studied were thermal treatment, reaction time, reactant volume, temperature and acid concentration. Leaching was carried out with hydrochloric acid. The small increase in extraction of aluminium after thermal treatment did not justify the calcination stage. For this reason the raw materials used were not calcined. Under optimum conditions, 84% of the aluminium was extracted. Aluminium to total iron extraction ratio was close to 0.7 and concentrations of 17.4 g/l of aluminium and 26.0 g/l of total iron were achieved. Analysis of iron distribution in the red soils showed that most of the iron was colloidal hematite covering the surface of the aluminous minerals. Taking advantage of this characteristic, tests were performed in order to obtain selective dissolution of iron and aluminium. Under optimal conditions the concentrations achieved were 29.6 g/l of aluminium and 13.1 g/l of total iron, which meant a threefold increase in comparison with the initial ratio of aluminium to total iron. Purification of these solutions was carried out by solvent extraction and then the hydrated aluminium chloride was precipitated by bubbling hydrogen chloride gas. Finally, the crystallised salt was thermally decomposed at 1073 K to yield an alumina having low iron and titanium contents.