Japan As Represented by Director General of Agency of Industrial Science

Shuji Tsunematsu

Eiichi Abe

Kozo Inoue

Hideo Yamada

Disclosed is an improvement in the process for the preparation of amorphous silicic acid particles useful, for example, as a filtration aid comprising the steps of a hydrothermal reaction to prepare calcium silicate particles and decalcification of the calcium silicate particles, after or without undertaking carbonation by the reaction of carbon dioxide, with an acid to form particles of amorphous silicic acid followed by drying of the amorphous silicic acid particles. Different from the conventional methods in which great shrinkage of the amorphous silicic acid cakes wet with water is unavoidable in the drying step to adversely affect the quality of the product, the final step of treatment preceding drying of the wet cake is undertaken in a liquid medium which is a mixture of water and a water-miscible organic solvent such as ethyl alcohol in a specified proportion so that the drying of the wet cake is performed without the disadvantage due to the large surface tension of water responsible to the drying shrinkage of wet cakes.

Method for the preparation of a high-quality powder of amorphous silicic

A novel method is proposed for the preparation of a calcium silicate powder particularly useful as a filter aid in the filtration of an acidic aqueous liquid by virtue of the extremely high acid resistance of the calcium silicate powder. The inventive method comprises a hydrothermal reaction of a blend of a silica-containing material and calcium oxide or hydroxide in a specified molar ratio under specified reaction conditions to form calcium silicate, which is then subjected to a heat treatment at 800.degree.-1200.degree. C. for 0.5-2 hours. An improvement can be obtained in the clarity of the filtrate obtained by the filtration using the calcium silicate powder prepared by the inventive method as a filter aid when the hydrothermal reaction for the preparation thereof is conducted in an aqueous solution of potassium hydroxide in a specified concentration.

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Tosu, Japan

Shuji Tsunematsu