GB1013950A - Process for the preparation of granulated phosphate fertilizers - Google Patents

Abstract

<PICT:1013950/C1/1> A granulated phosphate fertilizer, having a base of triple superphosphate, is prepared by mixing a substantially pulverulent triple superphosphate formed by treatment of phosphate mineral with concentrated phosphoric acid containing 46 to 55% by weight of P2O5, with a wet fluid superphosphate mass formed by treatment of phosphate mineral with dilute phosphoric acid containing 25 to 33% by weight of P2O5, and then granulating and drying the mixture. Part of this final mixture, preferably that left after removing the granules of the desired size by a screening operation, may be recycled. The fluid superphosphate preferably forms at least 20%, and the triple superphosphate in powdered form 70 to 85%, by weight of the final dry granulated triple superphosphate produced. A supplementary fertilizing compound, e.g. a potassium salt, may be added to the mixture prior to granulation. The process may be carried out continuously by controlling the rate of flow of the reactants. In relation to Fig. 1, previously ground phosphate mineral is fed into mixer 4, from hopper 1 via feed conveyer 2. Concentrated phosphoric acid at a controlled rate is fed into mixer 4. The mixture passes into rotatory drum 5, containing a scraper 6, and solidifies and is converted into powder form, and then passes into granulating drum 7. Phosphate mineral and dilute phosphoric acid are introduced into vat 11, and the thus-produced fluid superphosphate mass overflows into drum 7, where it mixes with the powdered triple superphosphate from drum 5. This mixture is dried in 13, and screened at 16. The granulated product of desired size is removed through 18, and the remaining particles are recycled to drum 7. Fig. 2 (not shown) includes a modification whereby a supplementary fertilizing compound may be introduced into drum 7.