| 摘要 |
<p>In the preparation of solutions of silica, for subsequent precipitation of silica in light form, from siliceous residues obtained by the decomposition of naturally-occurring silicates with suitable mineral acids, with concurrent production of concentrates of titanic acid when titanium oxide is present in the residues, the said residues are treated with hot solutions of alkali monocarbonate in a ratio of alkali monocarbonate to silica of, or equivalent to, not less than about 5Na2CO3: SiO2, whereby the solution of the decomposed silicate silica is effected with no or only negligible loss of carbonic acid and the subsequent precipitation of the greater part of the dissolved silica can be effected, under regulated conditions of cooling and agitation, without the addition of alkali carbonate or carbonic acid. The precipitated silica may be washed with water for partial removal of alkali, and may be freed from fixed or combined alkali by treatment with a suitable mineral acid and finally washing with water. In an example, a washed, dried, and ignited residue from the treatment of a natural silicate with sulphuric acid is treated with sodium carbonate solution at 90 DEG C. and the solution, after separation of insoluble matter, is agitated and cooled causing precipitation of silica, which is washed with wash liquors and then with water, treated with dilute sulphuric acid and again washed with water. Specification 294,681, [Class 1 (ii), Inorganic compounds, other than &c.], is referred to.</p> |
