GB721876A - Phosphate fertilisers and a process for their preparation - Google Patents

Abstract

<PICT:0721876/III/1> A fertilizer essentially comprising calcium phosphate is produced by melting a phosphate, and quenching and granulating the molten mass so that the resulting particles have to an extent of 95 per cent by weight a size of 0.05-1 mm. and a greater energy content that silico-carnotite. (The expression "greater energy content than silico-carnotite" is explained.) The particles have a vitreous structure. If larger grains are produced they are broken down; the 5 per cent by weight smaller than 0.05 mm. may be left in the product. The higher the ratio P2O5:other acids (SiO2, B2O3, Al2O3 &c.) in the product, the smaller should be the particles. Chilling may be effected with water or steam, except that in this case, the vitreous form is obtained only when there are present with the phosphates equivalent or even larger quantities of metasilicates, borates, aluminates, &c. Irrespective of the proportions of these substances present, chilling may be effected with air or other gas in the absence of water or steam; or by contact with cool surfaces e.g. water cooled metal sheets. Fig. 2 shows a device for granulating the molten phosphate, air under pressure being supplied via tubes 6, 7 annulus 5 and radial distribution tubes 8 to an annular slot 11. In another construction, air is supplied tangentially to an annular chamber communicating directly with the annular slot surrounding the nozzle. The surface of the molten phosphate, e.g. Thomas slag, to be quenched may be enlarged with an inflating or foaming agent, e.g. coal tar, &c. Thus, tar or other gas-evolving substance may be spread on the surface of the metal sheets; or air charged with coke dust is used to blow the slag out of the converter, or is directed against the slag flowing therefrom. Atomized oil may alternatively be used. In most instances, other than in the case of Thomas slag, the phosphates are melted in shaft furnaces, which may be fired under oxidizing conditions by oil or gas burners. When coke is used, producing reducing conditions, loss of phosphorus is minimized by adding iron, iron ore, or a phosphate rich in iron, or by melting the raw phosphate with blast furnace slag, or other vitrifying additives, e.g. magnesia-containing minerals and slags, aluminates, borates, silicates, alkali metal compounds and fluorides.