GB1050448A - - Google Patents

Abstract

1,050,448. Silica sol, gel and powder; metal silicates; Ca phosphate and sulphate. NIPPON CHEMICAL INDUSTRIAL CO. Ltd. June 27, 1963, No. 25651/63. Heading C1A. A silica sol containing less than 8% SiO 2 is obtained by reacting siliceous slag containing more than 5% SiO 2 with acid, in an acid concentration of up to 4M and in an amount approximately equivalent to the Ca content of the slag. The acid may be HCI, HNO 3 , H 2 SO 4 , H 3 PO 4 , formic, acetic, oxalic or. citric acid, or by-product waste acids, NaHSO 4 or SO 2 . A temperature below 40‹ C. may be used. The sol is separated from the solid residue, and may be treated to give:- (a) Pure sol by treating with (a) an alkaline earth metal oxide, hydroxide, carbonate to pH 4-5 (Example 7), (including lime, dolomite or magnesite), preferably after adding H 3 PO 4 or phosphate to remove Ca as Ca phosphate, (b) an ion exchange resin, e.g. strong or weak acid cationic, or weak basic anionic (Example 8), or (c) organic solvents. (b) Finely divided silica by adding proteins, e.g. gelatine, glue or albumen, or anionic, cationic, or non-ionic surface active agents. (Examples 9-11). After filtration, Ca(OH) 2 may be added to the filtrate to precipitate Ca 2 HPO 4 . (c) Finely divided silicate (i) by adding alkali metal or alkaline earth metal hydroxide or carbonate or alkali metal silicate to give Ca silicate (Examples 12, 21) or (ii) when the slag was treated with H 2 SO 4 , by adding alkali and a soluble metal salt, e.g. of Ca, Mg, Ba, Sr, Zn. Pb, Cd, Cu (Example 13). (d) Silica gel by (a) adjusting the pH and allowing to stand, (b) heating gently, (c) ageing and dropping into aqueous NH 3 , (d) dispersing in oil, or (e) gelling in the presence of alkali metal salts (Examples 14-17). (e) Silica-alumina gel by gelling in the presence of soluble Al salts, e.g. sulphate, chloride, or kalum, which may remain from a slag of high Al content, or may be added to the slag-acid mixture or to the sol. The sol is then (a) heated and alkali added, (b) neutralized with alkali and Na aluminate added, or (c) gelled in an inert organic solvent. Alternatively, the silica gel may be immersed in an Al salt solution (Examples 18, 19). Ca phosphate is precipitated from the crude sol by removing S04, e.g. with BaCO 3 , then adding a suspension of Ca(OH) 2 (Examples 7, 20). Gypsum is precipitated from the crude sol obtained when slag was treated with HCl or HNO 3 , by adding H 2 SO 4 or sulphate; or, when H 2 SO 4 was used to treat the slag, gypsum is separated from the solid residue.