Procédé de traitement des acides d'hydrolyse se formant dans la fabrication du dioxyde de titane par le procédé d'attaque à l'acide sulfurique

Hydrolysis acids, obtained in the production of titanium dioxide by the sulphuric acid decomposition process, are worked up by (1) pre-concentrating the hydrolysis acids with immersion heaters, (2) adding thick sludge from the concentrated acid produced in a previous cycle, (3) filtering off the separated salts from the acid which contains less than 70% H2SO4, (4) separating again the filtrate to a H2SO4 content of 93.5-95.0%, (5) decanting the concentrated acid from the freshly separated salts, (6) returning the thick sludge to the preconcentrated salt suspension, (7) granulating the sulphuric acid-containing filter cake with the addition of roasting residue, obtained from a sulphate decomposition furnace, and (8) transforming the granules into oxides and sulphur dioxide in an oil, tar, coal, coke, and/or sulphur-heated sulphate decomposition furnace. The hydrolysis acids may be briefly heated, preferably in the presence of titanium dioxide hydrate crystal seeds, to 140-180 DEG C. under an appropriate pressure prior to evaporation. The heat of the exhaust gases from the immersion heater may be used for a preliminary concentration of hydrolysis acids by means of indirectly heated heat exchangers under a vacuum or by sprinkling the heat exchanger with acid under normal pressure. An oxidizing agent, preferably nitric acid, a nitrate, a nitrite or a nitrosyl-sulphuric acid may be added to the pre-concentrated acid to convert any ferrous sulphate present to ferric, phosphoric acid or a phosphate may be added to the hydrolysis acids, prior to pre-concentration, in order to precipitate the titanium ions dissolved therein, the precipitate being separated. Ferrous sulphate heptahydrate may be added to the hydrolysis acids prior to preconcentration. The preheating of the acids may be done with expanded steam. Examples illustrate the process.