In addition to aluminum sulfate to produce sulfuric acid solutions essentially containing titanylsulfate

摘要

An aqueous solution containing water-soluble sulphuric acid salts of aluminium and titanium which may be employed for coating pigments is prepared by dissolving titanium dioxide in excess sulphuric acid of at least 75% H2SO4 concentration and thereafter adding hydrated alumina to the solution at a temperature of at least 100 DEG C. to reduce the excess acidity. The excess acid employed is at least 90% in excess of the amount required to form titanyl sulphate and the alumina addition is such that the amount of such excess is reduced to 0 to 80%. The titanium/aluminium ration, on an oxide basis, is preferably from 1:0,5 to 1:4. Thus titanium dioxide in the form of the finished pigment or as a pigment intermediate product may be dissolved in 95-97% sulphuric acid in the proportion from 2-13 mols. of sulphuric acid per mol of titanium dioxide at a temperature of 140-150 DEG C., the temperature being maintained by steam heating. Hydrated alumina may then be added at a 100-160 DEG C., after which the reaction medium is diluted with water to a concentration of 20-100 grams/litre of TiO2 and the solids residue separated by decanting or filtering. The final solution obtained may be employed to coat other pigments such as titanium dioxide, or titanates, or composite pigments such as titanium dioxide in admixture with barium sulphate or carbonate, or in admixture with zinc oxide. In such a case, after the solution has been mixed with the pigment, an acid binding substance such as the alkali, metal alkaline earth metal, magnesium and ammonium hydroxides, oxides or carbonate or organic bases are added. Alternatively the addition of the solution to the pigment to be treated may be effected in the presence of the acid binding agent.