GB1153176A - Fertilizers - Google Patents

Abstract

1,153,176. Phosphoric acid; phosphates; fertilizers. FISONS FERTILIZERS Ltd. 26 Sept., 1966 [13 Aug., 1965], No. 34850/65. Heading C1A. A continuous process for the production of a phosphate containing material comprises (i) acidulating phosphate rock with nitric acid (or a mixture thereof with e.g. sulphuric and/or phosphoric acid), (ii) simultaneously or subsequently adding (NH 4 ) 2 SO 4 , NH 4 HSO 4 or KHSO 4 to the reaction mixture in an amount of not less than 0À5 mole per mole of P 2 O 5 in the rock and at a rate such that dissolved sulphate concentration in the liquid phase is maintained in the range 0À5-4À0 wt. per cent, the addition being effected at above 60‹ C., and (iii) continuously removing the resulting acidic slurry containing precipitated calcium sulphate from the reaction system. This slurry is desirably neutralized (with or without prior removal by filtration of the calcium sulphate) e.g. with ammonia, an ammoniating solution, potassium carbonate or potassium hydroxide, and the product dried and/or granulated to produce a solid neutral fertilizer. The acidulation and sulphate addition may be performed in a multiple tank reaction system (cf. Specification 954,424). In the sulphate addition stage the calcium sulphate precipitates as gypsum between 60 and 90‹ C. and as hemihydrate or anhydrite at higher temperatures. In the preparation of fertilizers by the above method wherein the precipitated calcium sulphate is filtered off, sulphuric acid may be added to the reaction mixture prior to filtration and/or additional nitric acid or phosphoric acid after the filtration.