GB172087A - Improvements in the extraction of alumina - Google Patents

Abstract

Alkali metal compounds, obtaining from complex silicates Aluminium ores or aluminous material such as clay, slag or ashes are mixed with lime or equivalent calcium or magnesium compound in such quantity that there are at least 2 molecules of lime &c. for every molecule of silica and in addition, at least one molecule of lime &c. for every molecule of alumina. Allowance is made for any base that may be present in the ore &c. The materials are ground and calcined, a flux such as fluospar being added if desired. After cooling the product is treated with a solution of an alkali salt such as sodium carbonate to give alkali aluminate and an insoluble calcium or magnesium salt. The former is then treated for the production of alumina and alkali hydrate or carbonate by known processes. e.g. by the Bayer process or by passing lime-kiln gases. Any potash present in the raw material is rendered soluble and is recovered from the alkali left after precipitation of the alumina. Specification 9662/15, [Class 1 (iii), Oxides &c., Metallic], is referred to.ALSO:Aluminium ores or aluminous materials such as clay, slags, or ashes are mixed with lime or equivalent calcium or magnesium compound in such quantity that there are at least two molecules of lime &c. for every molecule of silica, and in addition at least one molecule of lime &c. for every molecule of alumina. Allowance is made for any base that may be present. The materials are finely ground and then calcined, a flux such as fluorspar being added if desired. After cooling and grinding, the product is treated with a solution of an alkali salt such as sodium carbonate in order to give alkali aluminate and an insoluble calcium or magnesium salt. The former is then treated for the production of alumina by known processes, e.g. by the Bayer process or by passing lime-kiln gases. The alkali-carbonate resulting from the latter method can be used for extracting further quantities of the calcined mass and the calcium silicate which is left after the extraction is particularly suitable in cement manufacture since it is free from insoluble alkali salts, no alkalis having been used in the calcination. Any potash present in the raw material is rendered soluble and is recovered from the alkali left after the precipitation of the alumina. In an example a blast-furnace slag containing principally alumina, silica and lime, but also magnesia, potash, and oxides of iron and manganese, is ground with limestone and 2 per cent of calcium fluoride added as a flux. The mixture is calcined and the cooled product boiled with sodium carbonate. The liquor is filtered and carbon dioxide passed into the hot filtrate to give alumina and sodium carbonate. Specification 9662/15 is referred to.