Production of di-calcium or di-magnesium phosphate and of mixed fertilisers containing the same

摘要

In obtaining dicalcium or dimagnesium phosphate by dissolving raw phosphate in hydrochloric or nitric acid, part of the solvent acid is driven off by adding the phosphate solution to a boiling solution of the calcium or magnesium salt of the respective solvent acid, the said solution having a higher boiling point than the acid. Precipitated dicalcium or dimagnesium phosphate and the newly-formed salt solution are removed, the phosphate then separated, and residual acid in the solution is neutralized by calcium carbonate present in fresh raw phosphate. By this means also, acid is saved in future lixiviation. Calcium chloride or nitrate may be recovered from the solution, say by evaporation. Alternatively, when nitric acid is employed, a mixed fertilizer may be obtained by drying together the dicalcium phosphate and newly-formed calcium nitrate. In another modification, potassium sulphate may be added to the phosphate solution, calcium sulphate separated, and a fertilizer consisting of dicalcium phosphate and potassium nitrate obtained by evaporating to dryness. The process may be worked continuously, for example, by mixing the phosphate solution and the boiling salt solution at the top of a separating column, while the acid solution containing the suspended phosphate flows off at the bottom. The Specification as open to inspection under Sect. 91 (3) (a) discloses also neutralization of the separated solution with lime or calcium carbonate. Claim is also made for the production of mixed fertilizers containing dimagnesium phosphate. This subject-matter does not appear in the Specification as accepted.ALSO:Fertilizers are obtained by dissolving raw phosphate in hydrochloric or nitric acid, and driving off part of the solvent acid by adding the phosphate solution to a boiling solution of the calcium or magnesium salt of the respective solvent acid; dicalcium or dimagnesium phosphate is precipitated. When nitric acid and a solution of calcium nitrate are employed, a mixed fertilizer may be obtained by drying together the dicalcium phosphate precipitated and the newly formed calcium nitrate. In a modification, potassium sulphate may be added to the phosphate solution, calcium sulphate separated, and a fertilizer consisting of dicalcium phosphate and potassium nitrate obtained by evaporating to dryness. In the Specification as open to inspection under Sect. 91 (3) (a) claim is made for the production of similar mixed fertilizers containing dimagnesium phosphate. This subject-matter does not appear in the Specification as accepted.