GB402977A - Improvements in process for the treatment of silicates with acids in order to obtaintheir soluble salts - Google Patents

Abstract

In a process of decomposing silicates, chiefly those containing the alkali metals sodium, potassium and lithium, by acid vapours such as of hydrochloric or nitric acids, the silicate and an aqueous solution of the acid are placed in the higher and lower parts respectively of a closed container; the liquid is heated to produce a vapour which condenses over the silicate, the condensate with the dissolved substances falling into the solution. The silicate may be admixed with substances capable of facilitating the reaction, e.g. kaolinised leucite. In an example, ground or granulated leucite is placed in a perforated container which is introduced into the top of a vertical tubular pressure-resisting autoclave which may be lined with grit sandstone. Slightly less than the theoretical quantity of nitric acid is used. Electric resistance, steam or direct fire heating is employed. The top of the autoclave may be slightly cooled, and the silicate may be periodically sprayed with liquid acid. The temperature should be maintained above 100 DEG C. to obviate the production of gelatinous silica, and preferably between the decomposition temperatures of iron and aluminium nitrates, viz. 125--140 DEG C. Any iron in the solution is precipitated under pressure by, say, potassium ferrocyanide, and removed, preferably by passage through the exhausted leucite. This is replaced by a fresh batch, and the hot solution in the autoclave evaporated to the desired extent by releasing the pressure, any residual acid vapours being removed by the fresh leucite. The potassium and aluminium nitrates are separated in known manner. Specification 401,567 is referred to.