| 摘要 |
<p>Titanium dioxide-bearing slag containing as an impurity at least one of the elements chromium or vanadium is leached with sulphuric acid containing ferric ions resulting in a titanium dioxide residue low in chromium and vanadium. Ferric ions can be introduced in various ways such as by pre-oxidation of the slag or by addition of oxidants such as air or an oxidizing chemical compound during leaching. The ferric ions may also be introduced by mixing ilmenite with the slag or by using an acid solution containing ferric ions as, for example, by adding ferric sulphate or by using acid previously used for leaching ilmenite. The slag and the ilmenite may be commonly ground so that about 90% by weight will pass a 325-mesh Tyler screen. Sulphuric acid waste acids as from the manufacture of TiO2 pigments may be used, the strength of which may be increased by evaporation or fortification. The acid strength may be from 15-60% and the temperature from 100 DEG to 250 DEG C. at pressures up to 500 p.s.i. The acid may be in, say 20%, excess. Lower temperatures require longer times or higher acid concentrations. For example at 200 DEG C. using 30/40% sulphuric acid the appropriate time is two hours.</p> |
