Process for the production of alumina hydrate, capable of forming with water, a colloidal solution, containing a high proportion of aluminum oxide and a very low proportion of acid radicals

摘要

Aluminium hydroxide containing basic aluminium salts of strong acids is rendered colloidally soluble in water by treating, preferably in the dry state, with steam at superatmospheric pressure. The initial material is prepared from an alkali metal aluminate solution by precipitation with a strong mineral acid or from an aluminium salt of a strong mineral acid, e.g. from aluminium chloride by reaction with caustic acid. In an illustrated embodiment, nitric acid is used to precipitate alumina from sodium aluminate the temperature being maintained at 40-50 DEG C. and the pH at 7.0-7.3; Bohmite is formed, which may be filtered, dried and ground and then treated with steam at 5-12 excess atmospheres whilst spread on stainless steel plates arranged on gratings in a pressure-tight chamber. If desired the chamber may subsequently be evacuated to facilitate removal of moisture from the alumina, and the product may be ground. A prior art statement refers to the preparation of colloidally soluble alumina by (1) peptizing precipitated aluminium hydroxide with an acid and evaporating the so-formed sol to dryness; (2) reacting a dilute aluminium amalgam with an aluminium salt solution or dilute monobasic mineral acid; (3) decomposing aluminium alcoholates with dilute acids; (4) electrolysing aluminium chloride solution; and (5) passing ethylene oxide into aluminium chloride solutions, distilling off the ethylene chlorhydrin and evaporating to dryness.