GB1420558A - Process for preparing gypsum - Google Patents

Abstract

1420558 Gypsum ISHIHARA SANGYO KAISHA Ltd 22 March 1974 [23 March 1973] 12929/74 Heading C1A Gypsum is prepared continuously by neutralizing sulphuric acid with a calcium compound by (a) mixing the calcium compound with a slurry of gypsum seed crystals to form a slurry mixture containing as CaO: CaSO 4 , 2H 2 O in the ratio 0À1-0À01 : 1, (b) continuously feeding the above slurry to a first inlet, and the sulphuric acid to a second inlet spaced from the first, of a reaction vessel (or vessels) in which stirring is effected in a horizontal plane to dilute the slurry mixture and sulphuric acid before contact and (c) continuously removing the overflow of the reaction mixture at a point separated from the inlet of the sulphuric acid at a rate to maintain a total residence time of the reaction mixture in the reaction vessel of 0À3-3 hours and removing the gypsum crystals from the reaction mixture so removed. A plurality of reaction vessels may be connected in series with the gypsum seed crystal slurry feed obtained from the reaction mixture of the preceding vessel. The calcium compound may be calcium carbonate, calcium hydroxide or calcium oxide. The sulphuric acid may be a waste sulphuric acid containing iron from a process for preparing titanium dioxide or a waste pickling acid or a dilute waste acid containing 10-400 g./l. of free H 2 SO 4 and 5-300 g./l. of Fe. The pH of the reaction mixture may be maintained in the range 3À5- 8À5.