GB796860A - Improvements in or relating to the production of mixed fertilisers - Google Patents

Abstract

<PICT:0796860/III/1> Granulated crude phosphate or superphosphate is treated simultaneously or successively with continuous agitation in a dish granulator with dilute sulphuric acid and aqueous ammonia to yield an ammoniated superphosphate containing excess acid which is then treated with concentrated aqueous ammonia or a solution of ammonium nitrate in aqueous ammonia to yield a granulated mixed fertilizer. The sulphuric acid is in a quantity at least sufficient to convert the initial phosphate into monocalcium phosphate (unless this has already been done) and to neutralize any excess ammonia, whilst the ammonia is supplied in an amount at least sufficient to convert the mono-calcium phosphate from the starting material into dicalcium phosphate by the formation of the ammonium salt of the attacking acid. At a 20 to 25 per cent ammonia solution is employed. The dish granulator employed consists of a disc provided with a peripheral wall, the disc being rotatable about a central axis perpendicular to to the disc and having means for adjusting the inclination of the axis of rotation. The dish granulator is preferably that described in Specification 796,861, and shown in the Figure. The disc 10 mounted on a pinion and ring gear indicated by 11, can be inclined at any desired angle about axis 12. The disc 10 is provided with annular channels formed by vertical walls 13. In operaton the granular phosphate to be treated is fed to the centre of the disc and the reactant solutions are supplied by lines 151, 152 to the central dish and by lines 153 and 154 to the outer and outermost annuli respectively. Pipes 151 and 152 may be employed to spray the phosphate with dilute sulphuric acid and aqueous ammonia or alternatively they may be employed to spray the material initially with water or with sulphuric, phosphoric or nitric acid where the starting material is finely powdered crude phosphate, in order to affect pre-granulation and decomposition of the crude phosphate. The pipes 153 and 154 are supplied with aqueous ammonia or an aqueous ammoniacal solution of ammonium nitrate to neutralize the acid ammoniated superphosphate falling into the outermost annuli from the central portion of the disc. The nozzles of the sprays 15 are arranged a short distance above the disc 10 in a direction substantially parallel with the surface of the disc. An adjustable scraper 19 on arm 20 is provided. Water escaping as steam is removed through a hood 16 and a pump 18 and the finished product falls over the outermost wall of the granulator for collection. According to examples: (1) granular superphosphate is treated with sulphuric acid and ammonia in the central space of a dish granulator provided with a single annular outer channel. The slightly acid granules pass over the inner wall into the annular channel where they are sprayed with an ammoniacal solution of ammonium nitrate. A product containing 7.5 per cent N and 12 per cent P2O5 was obtained; (2) a granular crude phosphate together with 50 per cent by weight of a potash fertilizer was fed in to the dish granulator and treated with sulphuric acid and ammonia and then subsequently with an aqueous ammoniating solution containing 41 per cent of nitrogen to produce a product containing 9 per cent N, 9 per cent P2O5 and 9 per cent K2O. Specification 709,613 is referred to.