The invention concerns a method for treating ferrous sulphate for the preparation of ferrous sulphate hydrate usable for chromium reduction in cement manufacture. According to the invention, sulphuric acid containing ferrous sulphate obtained as a side product from titanium dioxide production and which contains at the most appr. 30 % by weight of sulphuric acid, is neutralized with a CaO-containing material, preferably cement, in an amount sufficient to give a pH-value to the end product which is 1.5 to 5, whereby the reaction temperature is allowed to increase to at the most 120 °C.