Patent GB-726848-A (GB)
Title: Process for the production of an ammonium-citrate soluble fertilizer containing mainly secondary calcium phosphate
IPC: C05B11/06
Filed: 1953-03-27
Abstract: Secondary calcium phosphate is prepared by precipitation with ammonia from a mineral acid solution of raw phosphate in the presence of 0.5 to 4 per cent. by weight of a magnesium compound soluble in the solution, based on the weight of the raw phosphate. The preferred mineral acid is nitric acid.  The magnesium compound may be added to the phosphate, to the acid or the acid solution, or to the ammonia solution employed for precipitation.  The precipitation may be effected at above 55 DEG  C. to form an anhydrous phosphate, or the phosphate precipitated at lower temperatures may be dried at temperatures rising to 300 DEG  C.  The mother liquor remaining after separation of the secondary calcium phosphate may be treated with ammonia and carbon dioxide or ammonium carbonate to precipitate the calcium and magnesium content, leaving a useful solution of ammonium nitrate.  Alternatively, the latter precipitation may take place at the same time as the precipitation of the phosphate, in which case the solution resulting from the acid attack and containing the magnesium compound is neutralized with ammonia until a pH of 4 has been reached and the precipitation is continued with ammonia gas and carbon dioxide gas until a pH of 7 to 8 has been reached.  The combined precipitate is then filtered off.  Any excess ammonium carbonate remaining in the mother liquor may be neutralized with nitric acid to again obtain ammonium nitrate solution.  The precipitation of the phosphate with or without the remaining calcium may take place in stages in agitator vessels in commercial operation. According to examples (i) phosphate mixed with calcined magnesite is dissolved in nitric acid, and precipitation effected at about 40 DEG C. with an ammoniacal precipitating solution containing ammonium nitrate until a pH of 4 is reached.  Secondary calcium phosphate containing water of crystallisation is precipitated and separated. (ii) As in (i) above except that the magnesite is added to the solution resulting from the acid attack on the phosphate.  (iii) Phosphate is treated with nitric acid at 40 DEG  C. with agitation, and the temperature then raised to 50 DEG  C., whereupon a precipitating solution containing ammonia, ammonium nitrate and magnesium nitrate is added; after precipitation at a pH of 4, the filter cake obtained contains anhydrous secondary calcium phosphate and all the fluorine and other impurities of the raw phosphates.  The mother liquor containing ammonium nitrate, calcium nitrate and magnesium nitrate is precipitated at 60 DEG  C. with ammonium carbonate solution of a pH of 7 to 8 to obtain a precipitate of calcium carbonate containing a small amount of magnesium.  The ammonium nitrate solution remaining may be in part recirculated to prepare the precipitating solution; both the calcium carbonate and the ammonia nitrate solution, after evaporation, are suitable for making calcium ammonium nitrate. (iv) Phosphate is dissolved in nitric acid at 40 DEG  C. and calcined magnesite is then added. Precipitation is effected with ammonia/ammonium nitrate solution of 60 DEG C. at a pH of 4 and the precipitation is thereafter continued at the same temperature with ammonium carbonate solution until a pH of 7 to 8 has been reached.  The mixture is filtered and the precipitate washed and dried at 100 DEG  C.  The ammonium nitrate solution remaining may again be recycled to the process after having been saturated with ammonia gas.ALSO:A fertilizer comprising secondary calcium phosphate is prepared by precipitation with ammonia from a mineral acid solution of raw phosphate in the presence of 0.5 to 4 per cent. by weight of a magnesium compound soluble in the solution, based on the weight of the raw phosphate.  The preferred mineral acid is nitric acid. The magnesium compound may be added to the phosphate, to the acid or the acid solution, or to the ammonia solution employed for precipitation.  The precipitation may be effected at above 55 DEG C. to form an anhydrous phosphate, or the phosphate precipitated at lower temperatures may be dried at temperatures rising to 300 DEG C. The mother liquor remaining after separation of the secondary calcium phosphate may be treated with ammonia and carbon dioxide or ammonium carbonate to precipitate the calcium and magnesium content leaving a useful solution of ammonium nitrate. Alternatively, the latter precipitation may take place at the same time as the precipitation of the phosphate, in which case the solution resulting from the acid attack and containing the magnesium compound is neutralized with ammonia until a pH of 4 has been reached and the precipitation is continued with ammonia gas and carbon dioxide gas until a pH of 7 to 8 has been reached.  The combined precipitate is then filtered off.  Any excess ammonium carbonate remaining in the mother liquor may be neutralized with nitric acid to again obtain ammonium nitrate solution.  The precipitation of the phosphate with or without the remaining calcium may take place in stages in agitator vessels in commercial operation. According to examples, (i) phosphate mixed with calcined magnesite is dissolved in nitric acid, and precipitation effected at about 40 degrees C. with an ammoniacal precipitating solution containing ammonium nitrate until a pH of 4 is reached. Secondary calcium phosphate containing water of crystallisation is precipitated and separated.; (ii) as in (1) above except that the magnesite is added to the solution resulting from the acid attack on the phosphate; (iii) phosphate is treated with nitric acid at 40 DEG C. with agitation, and the temperature then raised to 50 DEG C. whereupon a precipitating solution containing ammonia, ammonium nitrate and magnesium nitrate is added; after precipitation at a pH of 4 the filter cake obtained contains anhydrous secondary calcium phosphate and all the fluorine and other impurities of the raw phosphates.  The mother liquor containing ammonium nitrate, calcium nitrate and magnesium nitrate is precipitated at 60 DEG C. with ammonium carbonate solution at a pH of 7 to 8 to obtain a precipitate of calcium carbonate containing a small amount of magnesium.  The ammonium nitrate solution remaining may be in part recirculated to prepare the precipitating solution, both the calcium carbonate and the ammonium nitrate solution, after evaporation, are suitable for making calcium ammonium nitrate; (iv) phosphate is dissolved in nitric acid at 40 DEG C. and calcined magnesite is then added. Precipitation is effected with ammonia/ammonium nitrate solution of 60 DEG C. at a pH of 4 and the precipitation is thereafter continued at the same temperature with ammonium carbonate solution until a pH of 7 to 8 has been reached.  The mixture is filtered and the precipitate washed and dried at 100 DEG C.  The ammonium nitrate solution remaining may again be recycled to the process after having been saturated with ammonia gas.