| 摘要 |
<p>Finely divided silicic acid is prepared from an alkali metal silicate solution with a molar ratio SiO2:M2O (where M is alkali) in the range 2.5:1 to 4.5:1 and a maximum concentration increasing with the above ratios but below 165 g. of SiO2 per litre, by heating said solution to over 100 DEG C. under pressure and separating ppted. silicic acid from the alkali metal silicate solution of reduced SiO2 content. The preferred concn. of SiO2 is 10-125 g./litre and the preferred temperature of reaction is 130-200 DEG C. Solid alkali metal silicate may be added to the resulting silicate solution to produce a fresh starting solution. The SiO2:M2O ratio may be lowered by adding MOH solution. The process may be carried out in a continuous manner, e.g. in an externally heated flow-tube, or in a multi-stage manner. The process may be used for purifying alkali metal silicate solutions since impurities, e.g. Fe, Al and Ti ions, are ppted. from the solution with the silicic acid.</p> |
