Patent GB-716566-A (GB)
Title: Improved process for manufacturing fertilisers
IPC: C05B11/06
Filed: 1952-01-17
Abstract: Citrate soluble phosphate fertilizers are prepared by attacking a natural phosphate which may or may not contain magnesium compounds with a mineral acid followed by neutralization of the resulting product, there being added to the product resulting from the acid attack, before it is dried, a magnesium compound decomposable in the acid attacked phosphate, to introduce magnesium ions representing from 0.1 to 2 per cent. of the weight of the finished fertilizer. The invention is particularly concerned with the attack by nitric acid, in which case it is preferred that the magnesium compound be introduced before neutralization and also that with the magnesium compound, sulphate ions in a quantity equal to the magnesium ion are introduced in proportion of 20 Mg ions and 20 SO4 for each hundred P2O5 ions.  50 per cent. strength nitric acid is preferred and the magnesium ions may be added in the form of oxides or salts such as carbonates, silicates, phosphates or naturally occurring substances containing these compounds.  The sulphate ion may be introduced as sulphuric acid or as an alkali or alkaline earth metal sulphate. Neutralization is preferably effected with ammonia which may be added until the pH of the liquid phase is about 10.  According to Examples (1) phosphate is attacked by 50 per cent. nitric acid and the paste obtained is treated with gaseous ammonia, to convert all the P2O5 into dicalcium phosphate; ammonia bicarbonate is then added to the mass to transform the calcium nitrate into calcium carbonate.  To the paste obtained dry product resulting from a previous operation and hydrated magnesium sulphate is added and the mixture granulated and dried.  (2) phosphate is attacked with nitric acid of 54 per cent. strength and to the product of the attack is added magnesium nitrate and calcium sulphate; ammonia is then injected and the paste cooled, after which carbon dioxide is introduced. Substantially all the phosphoric acid is soluble in ammonium citrate.  (3) phosphate is attacked with nitric acid of 54 per cent. strength, magnesium sulphate is added and ammonia introduced; after cooling carbon dioxide is injected and the mass is dried.  Before drying a potassium salt may be added to the p  fertilizer if desired.ALSO:Citrate soluble phosphate fertilizers are prepared by attacking a natural phosphate which may or may not contain magnesium compounds with a mineral acid followed by neutralization of the resulting product, there being added to the product resulting from the acid attack, before it is dried, a magnesium compound decomposable in the acid attacked phosphate, to introduce magnesium ions representing from 0.1 to 2 per cent of the weight of the finished fertilizer.  The invention is particularly concerned with the attack by nitric acid, in which case it is preferred that the magnesium compound be introduced before neutralization and also that with the magnesium compound, sulphate ions in a quantity equal to the magnesium ion are introduced in proportion of 20 Mg ions and 20 SO4 for each P2O5 ions. Fifty per cent nitric acid is preferred and the magnesium ions may be added in the form of oxides or salt such as carbonates, silicates, phosphates, or naturally occurring substances containing these compounds.  The sulphate ion may be introduced as sulphuric acid or as an alkali or alkaline earth metal sulphate.  Neutralization is preferably effected with ammonia which may be added until the pH of the liquid phase is about 10.  According to Examples, (1) phosphate is attacked by 50 per cent nitric acid and the paste obtained is treated with gaseous ammonia, to convert all the P2O5 into dicalcium phosphate; ammonia bicarbonate is then added to the mass to transform the calcium nitrate into calcium carbonate.  To the paste obtained dry product resulting from a previous operation and hydrated magnesium sulphate is added and the mixture granulated and dried. (2) phosphate is attacked with nitric acid of 54 per cent strength and to the product of the attack is added magnesium nitrate and calcium sulphate; ammonia is then injected and the paste cooled, after which carbon dioxide is introduced. Substantially all the phosphoric acid is soluble in ammonium citrate.  (3) phosphate is attacked with nitric acid of 54 per cent strength, magnesium sulphate is added and ammonia introduced; after cooling carbon dioxide is injected and the mass is dried. Before drying a potassium salt may be added to the fertilizer if desired.