Patent GB-789978-A (GB)
Title: A process for drying moist salt mixtures produced in the manufacture of compound fertilisers and improved salt mixtures prepared by such a process
IPC: C05B19/00
Filed: 1954-07-27
Abstract: In the drying of a moist salt mixture containing 5 to 25 per cent of water, produced in the manufacture of compound fertilizers by attacking phosphate with nitric, sulphuric or phosphoric acids and subsequent neutralization, the mass to be dried contains, prior to the drying, at least 8 per cent calcium sulphate and at least 2 per cent of potassium sulphate, at least one of these substances being added after neutralization.  Calcium sulphate is preferably present in an amount between 8 and 20 per cent, and potassium sulphate in an amount between 2 and 5 per cent, and either of these substances may be present as a result of the manufacturing process itself.  The moisture content of the salt mixture may be reduced to 3 to 7 per cent after the sulphate addition by the addition of already dried material of the same composition and the drying is suitably effected at 50 DEG  to 180 DEG  C. down to a final water content of about 1 per cent.  The joint action of the two sulphates appears to result in the formation of syngenite.  According to examples: (1) Moroccan phosphate was decomposed with nitric acid and thereafter neutralized with gaseous ammonia at 2.5 atmospheres pressure.  The resulting mass containing 20.5 per cent of water was mixed with potassium chloride, potassium sulphate and gypsum and the highly viscous mass was thereafter granulated and dried at 80 DEG  to 120 DEG  C. down to a water content of 1.25 per cent; (2) Moroccan phosphat was attacked with nitric acid and the mixture neutralized with gaseous ammonia under pressure while simultaneously adding sulphuric acid. The resulting paste, already containing calcium sulphate was mixed with potassium chloride and a smaller amount of potassium sulphate and granulated by adding twice the quantity of re-cycled material and thereafter drying at 80 DEG  to 120 DEG  C.; (3) Moroccan phosphate was attacked with phosphoric acid and the mass neutralized with gaseous ammonia and thereafter mixed with potassium chloride, potassium sulphate and gypsum.  The material was then granulated as before; (4) Moroccan phosphate was attacked with nitric acid and neutralized with ammonia under pressure and the neutralized mixture was mixed with potassium sulphate.  Its water content was 13 per cent.  Gypsum was then added and thereafter a quantity of dried re-cycled material; the final mixture with a water content of 5.7 per cent was granulated and dried at 80 DEG  to 120 DEG  C.ALSO:In the drying of a moist salt mixture containing 5 to 25 per cent of water, produced in the manufacture of compound fertilizers by attacking phosphate with nitric, sulphuric or phosphoric acids and subsequent neutralization, the mass to be dried contains, prior to the drying, at least 8 per cent calcium sulphate and at least 2 per cent of potassium sulphate, at least one of these substances being added after neutralization.  Calcium sulphate is preferably present in an amount between 8 and 20 per cent, and potassium sulphate in an amount between 2 and 5 per cent, and either of these substances may be present as a result of the manufacturing process itself.  The moisture content of the salt mixture may be reduced to 3 to 7 per cent after the sulphate addition by the addition of already dried material of the same composition and the drying is suitably effected at 50 DEG  to 180 DEG C. down to a final water content of about 1 per cent.  The joint action of the two sulphates appears to result in the formation of syngenite.  According to examples (1) Moroccan phosphate was decomposed with nitric acid and thereafter neutralized with gaseous ammonia at 2,5 atmospheres pressure.  The resulting mass containing 20,5 per cent of water was mixed with potassium chloride, potassium sulphate and gypsum and the highly viscous mass was thereafter granulated and dried at 80 DEG  to 120 DEG C. down to a water content of 1,25 per cent.  (2) Moroccan phosphate was attacked with nitric acid and the mixture neutralized with gaseous ammonia under pressure while simultaneously adding sulphuric acid.  The resulting paste, already containing calcium sulphate was mixed with potassium chloride and a smaller amount of potassium sulphate and granulated by adding twice the quantity of re-cycled material and thereafter drying at 80 DEG  to 120 DEG C. (3) Moroccan phosphate was attacked with phosphoric acid and the mass neutralized with gaseous ammonia and thereafter mixed with potassium chloride, potassium sulphate and gypsum.  The material was then granulated as before. (4) Moroccan phosphate was attacked with nitric acid and neutralized with ammonia under pressure and the neutralized mixture was mixed with potassium sulphate.  Its water content was 13 per cent.  Gypsum was then added and thereafter a quantity of dried recycled material; the final mixture with a water content of 5,7 per cent was granulated and dried at 80 DEG  to 120 DEG C.