Patent GB-735308-A (GB)
Title: Improvements in the manufacture of phosphated fertilisers
IPC: C05B11/04
Filed: 1952-06-20
Abstract: In a process for manufacturing phosphate fertilizer by attacking phosphates with a mineral acid followed by the addition of a neutralizing agent, aluminium ions in a proportion of at least 20 gram ions of aluminium per 100 gram molecules of P2O5 are introduced after the addition of the mineral acid but before the addition of the neutralizing agent.  The aluminium may be introduced as silicate, silicoaluminate, phosphate, oxide, sulphate or nitrate, and after the addition thereof the acid attacked mass may be treated with a large excess of neutralizing agent without forming citrate insoluble phosphate.  The final pH may reach the value of 10.  The preferred mineral acid is nitric acid and neutralization may be effected by lime, calcium carbonate or ammonia.  In order to eliminate calcium nitrate from the final product, after the acid attack and the introduction of aluminium ions, sulphate or phosphate radicals may be added in the form of the acids which are introduced at the same time as the ammonia in such proportions as will combine with the calcium not combined as dicalcium phosphate with the simultaneous production of ammonium nitrate.  Alternatively carbon-dioxide gas may be employed to fix the lime as carbonate, in which case before neutralization a quantity of sulphuric ions stoichiometrically equivalent to the introduced aluminium ions are added in the form of sulphuric acid or as a sulphate such as gypsum.  According to examples (i) phosphate is attacked with hydrochloric acid of a density of 1.16 and after stirring for 2 hours hydrated aluminium oxide is added followed by slaked lime in the form of lime wash; the dicalcium phosphate is filtered, washed and dried: 99.6 per cent of the phosphate content is citrate soluble; (ii) phosphate is attacked with nitric acid and hydrated aluminium sulphate is added to the paste obtained followed, whilst stirring, by the addition of gaseous ammonia.  After the ammonia addition, carbon dioxide gas is introduced into the paste and the mass dried to obtain a fertilizer containing 8.45 per cent each of nitric and ammoniacal nitrogen and 12.7 per cent of phosphoric acid of which 99.3 per cent was citrate soluble.  If the aluminium were introduced in a form other than the sulphate, sulphate ions should be added.ALSO:In a process for manufacturing phosphate fertilizer by attacking phosphates with a mineral acid followed by the addition of a neutralizing agent, aluminium ions in a proportion of at least 20 gram ions of aluminium per 100 gram molecules of P2O5 are introduced after the addition of the mineral acid but before the addition of the neutralizing agent. The aluminium may be introduced as silicate, silico-aluminate, phosphate, oxide, sulphate or nitrate, and after the addition thereof the acid attacked mass may be treated with a large excess of neutralizing agent without forming citrate insoluble phosphate.  The final pH may reach the value of 10.  The preferred mineral acid is nitric acid and neutralization may be effected by lime, calcium carbonate or ammonia.  In order to eliminate calcium nitrate from the final product, after the acid attack and the introduction of aluminium ions, sulphate or phosphate radicals may be added in the form of the acids which are introduced at the same time as the ammonia in such proportions as will combine with the calcium not combined as dicalcium phosphate with the simultaneous production of ammonium nitrate.  Alternatively carbon-dioxide gas may be employed to fix the lime as carbonate, in which case before neutralization a quantity of sulphuric ions stoichiometrically equivalent to the introduced aluminium ions are added in the form of sulphuric acid or as a sulphate such as gypsum.  According to examples (i) phosphate is attacked with hydrochloric acid of a density of 1.16 and after stirring for two hours hydrated aluminium oxide is added followed by slaked lime in the form of lime wash; the dicalcium phosphate is filtered, washed and dried.  99.6 per cent of the phosphate content is citrate soluble.  (ii) Phosphate is attacked with nitric acid and hydrated aluminium sulphate is added to the paste obtained followed, whilst stirring, by the addition of gaseous ammonia.  After the ammonia addition, carbon dioxide gas is introduced into the paste and the mass dried to obtain a fertilizer containing 8.45 per cent each of nitric and ammoniacal nitrogen and 12.7 per cent of phosphoric acid of which 99.3 per cent was citrate soluble.  If the aluminium were introduced in a form other than the sulphate, sulphate ions should be added.