Chiyoda Chemical Engineering Construction Co., Ltd.

Takashi Sendo

Sachio Asaoka

Munekazu Nakamura

An improved method of preparing alumina, including a first stage in which an alumina hydrogel is formed from seed aluminum hydroxide, and a second stage in which the alumina hydrogel is processed for conversion into alumina. The improvement is in the first stage, comprising the steps of: (a) providing an aqueous slurry containing seed aluminum hydroxide and (b) mixing a pH controlling agent with the aqueous slurry to adjust the pH of the aqueous slurry to a value less than 5 or more than 11 and to dissolve fine crystallites of aluminum hydroxide contained in the aqueous slurry, the pH controlling agent being substantially free of ions which can form a precipitate during the first step, and then (c) then mixing an alumina compound with the aqueous slurry to adjust the pH of the aqueous slurry to a value in the range of from 6 to 11 and to cause the seed aluminum hydroxide to grow, the steps (b) and (c) being repeated in sequence more than once so that the seed aluminum hydroxide is caused to grow into the alumina hydrogel.

Method of preparing alumina

An improved process for the preparation of alumina, including forming an alumina hydrogel from aluminum hydroxide, and processing the alumina hydrogel into alumina. The improvement involves the alumina hydrogel forming step which is connected in the presence of sulfate ion and which comprises providing, in a reaction zone, an aqueous slurry containing seed aluminum hydroxide and having a pH of 6-11, and feeding to the reaction zone an aluminum compound and a pH controlling agent for mixing with the aqueous slurry while maintaining the aqueous slurry at a temperature of at least about 50.degree. C. at feed rates so that the pH of the aqueous slurry is maintained within the range of 6-11 and that 0.2-5 mols/hour of aluminum components, in terms of elemental aluminum, are fed to the reaction zone per mole of the seed aluminum hydroxide originally contained in the aqueous slurry, whereby the seed aluminum hydroxide is caused to grow to the aluminum hydrogel.

Growing community of inventors

Machida, Japan

Takashi Sendo