Patent GB-655938-A (GB)
Title: Process for directly obtaining non-hygroscopic fertilizers
IPC: C05B11/06
Filed: 1947-03-04
Abstract: In making non-hygroscopic fertilizers containing water-soluble and citrate-soluble phosphoric acid by reacting crude phosphate with nitric acid, which may contain ammonium nitrate, and precipitating a part or the whole of the calcium by the action of a sulphate, bisulphate or sulphuric acid or any mixture thereof, the paste resulting from these operations is neutralized by tetracalcium phosphate in the form of basic slag.  Sulphates specified are potassium and ammonium sulphates.  The Specification as open to inspection under Sect. 91 comprises also reacting crude phosphate with nitric acid, preferably in a dilute medium such as a solution of ammonium nitrate or calcium nitrate and ammonia, optionally separating the gangue, adding ammonia either in stages to precipitate monocalcium phosphate and then dicalcium phosphate which is separately filtered, and converting the calcium nitrate in solution by carbon dioxide into calcium carbonate, which is filtered or decanted and dried. Instead of carbon dioxide, phosphoric acid may be used to eliminate calcium remaining in solution after precipitation of the dicalcium phosphate, and subsequent neutralization may be effected with bases other than ammonia, e.g. calcium oxide and alkaline earth salts of weak acids, such as calcium carbonate, magnesium carbonate, dicalcium phosphate, tricalcium phosphate, or their derivatives silicocarnotite, Ca3(PO4)2.CaSiO3.CaO and steatite, 3Ca3(PO4)2.CaSiO3.3CaO.  This subject-matter does not appear in the Specification as accepted.ALSO:In making non-hygroscopic fertilizers, which are of granular form before drying and contain water soluble and citrate soluble phosphoric acid, by reacting crude phosphate with nitric acid which may contain ammonium nitrate and precipitating a part of the whole of the calcium by the action of a sulphate, bisulphate or sulphuric acid or any mixture thereof, the paste resulting from these operations is neutralized by tetracalcium phosphate in the form of basic slag.  Sulphates specified are potassium and ammonium sulphates.  Potassium chloride or any other salt may be added to the mixture.  The Specification as open to inspection under Sect. 91 comprises also reacting crude phosphate with nitric acid, preferably in a dilute medium such as a solution of ammonium nitrate or calcium nitrate and ammonia, optionally separating the gangue, adding ammonia either in stages to precipitate monocalcium phosphate and then dicalciumphosphate which may be separately filtered, or in one bath to precipitate dicalciumphosphate, and converting the calcium nitrate in solution by carbon dioxide into calcium carbonate, which is filtered or decanted and dried and may contain up to 10 per cent ammonium nitrate, additional ammonium nitrate being added, if desired, in solid form or in solution.  The final solution containing ammonium nitrate may be concentrated in known manner.  Potassium sulphate may be added to the dicalcium phosphate, after drying, in amount corresponding to the calcium nitrate or calcium and ammonium nitrates retained, to give ternary fertilizers containing respectively (a) Ca2H2(PO4)2, NH4NO3, KNO3, and CaSO4, and (b) Ca2H2(PO4)2, NH4NO3, (NH4)2SO4, KNO3 and CaSO4.  Instead of carbon dioxide, phosphoric acid may be used to eliminate calcium remaining in solution after precipitation of the dicalcium phosphate, and subsequent neutralization may be effected with bases other than ammonia, e.g. calcium oxide and alkaline earth salts of weak acids, such as calcium carbonate, magnesium carbonate, dicalcium phosphate, tricalcium phosphate or their derivatives silico-carnotite Ca3(PO4)2, CaSiO3, CaO. and steatite 3 Ca3(PO4)2, CaSiO3, 3 CaO.  This subject-matter does not appear in the Specification as accepted.