GB791004A - Improvements in or relating to the manufacture of granulated mixed fertilisers - Google Patents

Abstract

A granulated mixed fertilizer with a high nitrogen and potassium content and a low phosphate content is produced by treating an aqueous solution of phosphoric acid with ammonia gas, adding sulphuric acid and ground phosphate rock to the ammoniated acid to form a slurry, adding ammonium sulphate and potassium chloride or sulphate to the slurry and granulating the final product. The sulphuric acid may be admixed with the phosphoric acid prior to ammoniation if the ammoniation is to be carried out to the mono-ammonium phosphate stage only, but if further ammoniation is required the sulphuric acid must be added afterwards. In the latter case the sulphuric acid may be added with the phosphate rock or prior to adding the phosphate rock, or it may be reacted with the phosphate rock and the resulting super phosphate sludge may be added to the ammoniated phosphoric acid. The resulting granular mixed fertilizers contain at least 35 plant food units (i.e., the combined nitrogen, phosphate (as P2O5) and potash (as K2O) totals 35 per cent or over), and the ratios of nitrogen to phosphorus and potassium to phosphorus (calculated as elements) is at least 2,5).