Patent GB-353160-A (GB)
Title: Improvements in and relating to the treatment of phosphate material
IPC: C05B11/06
Filed: 1930-05-27
Abstract: Ammonium nitrate and phosphates; calcium nitrate and phosphates; alkali nitrates.--Rock phosphate is dissolved in nitric acid, a substantial part of the calcium is crystallized from the solution as calcium nitrate and the resulting mother liquor is treated with ammonia and/or ammonium carbonate to precipitate calcium phosphates which are returned directly or after further treatment to be acted upon, in addition to fresh rock phosphate, with nitric acid, the remaining solution containing ammonium phosphate and/or ammonium nitrate being worked up for the production of fertilizers &c.  Excess of ammonia and/or ammonium carbonate may be employed, the excess being subsequently removed by distillation for further use.  The precipitation of calcium phosphates is preferably carried out in a closed vessel under pressure.  According to one example the mother liquor after the removal of some calcium nitrate is treated with sufficient ammonia to precipitate tricalcium phosphate which is removed and returned to the process, a solution of ammonium nitrate and ammonium phosphate remaining which is evaporated with or without the addition of potash salts to form mixed fertilizers. In a second example, the calcium is precipitated as dicalcium phosphate the remaining solution being treated as in the previous example and the dicalcium phosphate being either returned to the process as before, treated with ammonia to produce a precipitate of tricalcium phosphate which is returned to the process and a solution of diammonium phosphate or with ammonium carbonate to produce a mixed precipitate of calcium carbonate and dicalcium phosphate which is returned to the process and a solution of diammonium phosphate.  In a third example the crystallization as calcium nitrate is limited so that upon subsequent treatment with ammonia the whole of the calcium and phosphoric acid is precipitated as dicalcium phosphate, a solution of ammonium nitrate remaining, the dicalcium phosphate being treated as in the second example.  In a fourth example, the mother liquor after crystallization of calcium nitrate is distilled whereby nitric acid is removed, the remaining solution of mono-calcium phosphate being treated with ammonia with or without ammonium carbonate, a precipitate of calcium phosphates with or without carbonate and a solution of diammonium phosphate being produced.  When tricalcium phosphate is precipitated it may be treated with hydrochloric acid to convert it to dicalcium phosphate which is returned into the process, a saving of nitric acid resulting. Specifications 339,340 and 339,969, [both in Class 1 (ii), Inorganic compounds other than &c.], are referred to.  The Specification as open to inspection under Sect. 91 (3) (a) comprises also the use of lime, calcium carbonates, or alkali carbonate as precipitants instead of ammonia, calcium nitrate or alkali nitrates being formed.  The subject-matter does not appear in the Specification as accepted.ALSO:Rock phosphate is dissolved in nitric acid, a substantial part of the calcium is crystallized from the solution as calcium nitrate and the resulting mother liquor is treated with ammonia and/or ammonium carbonate to precipitate calcium phosphates which are returned directly or after further treatment to be acted upon, in addition to fresh rock phosphate, with nitric acid, the remaining solution containing ammonium phosphate with or without ammonium nitrate being worked up for the production of fertilizers &c.  Excess of ammonia and/or ammonium carbonate may be employed, the excess being subsequently removed by distillation for further use. The precipitation of calcium phosphate is preferably carried out in a closed vessel under pressure. According to one example the mother liquor after the removal of some calcium nitrate is treated with sufficient ammonia to precipitate tri-calcium phosphate which is removed and returned to the process, a solution of ammonium nitrate and ammonium phosphate remaining which is evaporated with or without the addition of potash salts to form mixed fertilizers.  In a second example, the calcium is precipitated as dicalcium phosphate the remaining solution being treated as in the previous example and the dicalcium phosphate being either returned to the process as before, treated with ammonia to produce a precipitate of tri-calcium phosphate which is returned to the process and a solution of diammonium phosphate or with ammonium carbonate to produce a mixed precipitate of calcium carbonate and di-calcium phosphate which is returned to the process and a solution of di-ammonium phosphate. Specifications 339340 and 339,969, [both in Class 111, Sewage &c.], are referred to.  The Specification as open to inspection under Sect. 91 (3) (a) comprises also the use of lime, calcium carbonates or alkali carbonate as precipitants instead of ammonia, calcium nitrate or alkali nitrates being formed.  The subject-matter does not appear in the Specification as accepted.