Patent ID: 8128903

Claim:
Method for controlling the solubility of granular material, the method comprising following steps: obtaining an amount of a crude precipitate comprising iron(II)sulphate monohydrate and sulphuric acid from titanium dioxide production, mixing the said precipitate and a neutralising agent in a mixing apparatus to obtain a reaction mixture, the temperature during mixing of the reaction mixture being allowed to increase at the most to a temperature of 120° C., characterised in mixing water with the reaction mixture in the said mixing apparatus, and keeping the amount of neutralising agent sufficient to give a pH value from 1.5 to 4 to the end product in order to obtain a granular material having a high soluble iron(II) content or keeping the amount of neutralising agent sufficient to give a pH value ≧9 to the end product in order to obtain a granular material having a low solubility.