GB1187952A - Improvements in the Manufacture of PhosphonitrogenousFertilisers. - Google Patents

Abstract

1,187,952. Ammonium phosphates. POWERGAS CORP. Ltd. 7 July, 1967 [8 July, 1966], No. 30688/66. Heading C1A. In making a phosphonitrogenous fertilizer, phosphate rock is acidulated with H 2 SO 4 so that a part of the calcium present in the rock is converted to CaSO 4 , the temperature being such as to give a precipitate of gypsum or hemihydrate, this product is then reacted with nitric acid so that substantially all the P 2 O 5 initially present in the rock is converted into H 3 PO 4 , Ca(NO 3 ) 2 also being formed, (NH 4 ) 2 SO 4 is added sufficient to convert the calcium present in solution into CaSO 4 , precipitated as gypsum, the CaSO 4 is removed and the reaction product withdrawn and neutralized with ammonia to convert any free phosphoric acid present into ammonium phosphate. Preferred temperatures for the acidulation with H 2 SO 4 are 60‹ to 90‹ C. or at least 90‹ C. For the addition of (NH 4 ) 2 SO 4 the range 60‹ to 90‹ C. is preferred. In a preferred embodiment the P 2 O 5 in the phosphate rock is converted in part to monocalcium phosphate and part to phosphoric acid during the initial acidulation. A potassium salt or potassium hydroxide may be added to a product solution in which the ammonium phosphate present is monoammonium phosphate to convert some or all of the mono-ammonium phosphate into diammonium phosphate and potassium hydrogen phosphate. The CaSO 4 produced by the acid treatment may be converted to CaCO 3 by reaction with ammonia and carbon dioxide, the (NH 4 ) 2 SO 4 solution produced being used in the process. An example of the process is given using Nauru phosphate rock.