Improved method of purifying hot spent pickle liquors from steel mills, and the like

摘要

Hot spent pickle liquor containing sulphuric acid and ferrous sulphate has incorporated therein sufficient alkaline-earth metal carbonate to provide an excess of 15-20 per cent over that theoretically required to neutralize the entire free acid content of the liquor and the liquor then agitated until its pH value is between 6,0 and 7,0; the hydrolysis of the ferrous sulphate present is then rendered continuous and complete by having present sufficient carbonate to neutralize the sulphuric acid formed thereby and oxidizing the ferrous hydroxide to ferric hydroxide. The operation is preferably carried out in two stages with removal of the sludge of calcium or like sulphate formed in the first stage, and the oxidation of the ferrous hydroxide is effected by air preferably at temperatures of 100 DEG C. or higher and preferably also under pressure.ALSO:Hot spent pickle liquor from steel mills &c. is freed from sulphuric acid and ferrous sulphate by incorporating therein sufficient alkaline-earth carbonate to provide an excess of 15-20 per cent over that theoretically required to neutralize the entire free acid content of the liquor and then agitating until the pH value is between 6,0 and 7,0; the hydrolysis of the ferrous sulphate is then rendered continuous and complete by having present sufficient carbonate to neutralize the sulphuric acid formed thereby and oxidizing the ferrous hydroxide to ferric hydroxide. The operation is preferably carried out in two stages with removal of the sludge of calcium or like sulphate formed in the first stage, and the oxidation of the ferrous hydroxide is effected by air preferably at temperatures of 100 DEG C. or higher and preferably also under pressure. The purified effluent containing dissolved calcium sulphate may be softened by treatment with soda ash.