Patent GB-343701-A (GB)
Title: Method of treating solutions obtained in leaching phosphate rock with nitric acid and ammonium sulphate
IPC: C05B11/06
Filed: 1930-01-21
Abstract: The solution obtained by leaching phosphate rock with nitric acid and ammonium sulphate and removing the calcium sulphate and insoluble impurities, is neutralized with ammonia to a point at which either all mono- or all diammonium phosphate is formed, concentrated by evaporation, and cooled to crystallize the chief portion of said ammonium phosphate, mixed or not with varying proportions of ammonium nitrate, dependent on the degree of evaporation, and the mother liquor, containing chiefly ammonium nitrate, is purified by precipitation of the remaining phosphate, and evaporated to obtain the pure nitrate.  If diammonium phosphate is required the solution is first neutralized to give the mono salt, or a mixture thereof with the diammonium salt, and the further quantity of ammonia only added after the solution has been filtered from the precipitated phosphates of calcium, aluminium, iron, and other impurities, and concentrated by evaporation.  The mother liquor after crystallization of the phosphate may be treated, preferably at a temperature above 80 DEG C., with a calcium compound such as the nitrate, a little ammonia also being added if mono-ammonium phosphate is present, to precipitate calcium phosphate which may be returned to the leaching process.  The ammonium sulphate used in the leaching may be produced from calcium sulphate obtained in the process, by treatment with ammonium carbonate or ammonia and carbon dioxide, and the calcium carbonate formed added to the ammonium nitrate for use as a fertilizer, or part of it converted into calcium nitrate for precipitating the phosphates.ALSO:The solution obtained by leaching phosphate rock with nitric acid and ammonium sulphate, and removing the calcium sulphate and insoluble impurities, is neutralized with ammonia to a point at which either all mono- or all diammonium phosphate is formed, concentrated by evaporation, and cooled to crystallize the chief portion of said ammonium phosphate, mixed or not with varying proportions of ammonium nitrate, dependent on the degree of evaporation, and the mother liquor, containing chiefly ammonium nitrate, is purified by precipitation of the remaining phosphate, and evaporated to obtain the pure nitrate.  If diammonium phosphate is required the solution is first neutralized to give the mono salt, or a mixture thereof with the diammonium salt, and the further quantity of ammonia only added after the solution has been filtered from the precipitated phosphates of calcium, aluminium, iron, and other impurities, and concentrated by evaporation.  The mother liquor after crystallization of the phosphate may be treated, preferably at a temperature above 80 DEG  C., with a calcium compound such as the nitrate, a little ammonia also being added if monoammonium phosphate is present, to precipitate calcium phosphate which may be returned to the leaching process.  The ammonium sulphate used in the leaching may be produced from calcium sulphate obtained in the process, by treatment with ammonium carbonate or ammonia and carbon dioxide, and the calcium carbonate formed added to the ammonium nitrate for use as a fertilizer, or part of it converted into calcium nitrate for precipitating the phosphates.