GB411575A - Improvements in the manufacture and production of mixed fertilisers - Google Patents

Abstract

Mixed fertilizers are obtained by decomposing crude calcium phosphate with sufficient nitric acid to produce free phosphoric acid and calcium nitrate, dividing the decomposition solution into two parts, precipitating the lime in one part by the addition of ammonium sulphate, separating the precipitate, treating the mother liquor with excess of ammonia to precipitate tri-ammonium phosphate leaving a solution of ammonium nitrate and finally separating the tri-ammonium phosphate and adding it to the other part of the decomposition solution. Alternatively, the crude phosphate is divided into two parts, one part being decomposed with nitric acid and the other with nitric acid and ammonium sulphate. Ammonium nitrate solution, ammonia and/or nitric acid with or without potassium salts such as potassium chloride may be added to the mixture of tri-ammonium phosphate and the other part of the decomposition solution, or to one of the components. The tri-ammonium phosphate may be heated to drive off some of its ammonia before it is added to the other part of the decomposition solution. The tri-ammonium phosphate may be precipated, say at -5 to -10 DEG C., by means of gaseous ammonia obtained by evaporating liquid ammonia, the cold produced in the evaporation being utilized. The precipitated calcium sulphate may be reacted with ammonia and carbon dioxide to reform ammonium sulphate for reuse in the process and calcium carbonate which may be worked up with the ammonium nitrate solution withdrawn from the process to produce a mixed fertilizer consisting of calcium carbonate and ammonium nitrate. According to the Provisional Specification, the lime may be precipitated by means of alkali metal sulphates or mixtures thereof instead of ammonium sulphate; when employing potassium sulphate, it is preferable to separate potassium nitrate from the acid solution before the treatment with ammonia. Examples are given.ALSO:Mixed fertilizers are obtained by decomposing crude calcium phosphate with sufficient nitric acid to produce free phosphoric acid and calcium nitrate, dividing the decomposition solution into two parts, precipitating the lime in one part by the addition of ammonium sulphate, separating the precipitate, treating the mother liquor with excess of ammonia to precipitate tri-ammonium phosphate leaving a solution of ammonium nitrate and finally separating the tri-ammonium phosphate and adding it to the other part of the decomposition solution. Alternatively, the crude phosphate is divided into two parts, one part being decomposed with nitric acid and the other with nitric acid and-ammonium sulphate. Ammonium nitrate solution, ammonia and/or nitric acid with or with out potassium salts such as potassium chloride may be added to the mixture of tri-ammonium phosphate and the other part of the decomposition solution, or to one of the components. The tri-ammonium phosphate may be heated to drive off some of its ammonia before it is added to the other part of the decomposition solution. The tri-ammonium phosphate may be precipated, say at -5 to-10 DEG C., by means of gaseous ammonia obtained by evaporating liquid ammonia, the cold produced in the evaporation being utilized. The precipitated calcium sulphate may be reacted with ammonia and carbon dioxide to reform ammonium sulphate for reuse in the process and calcium carbonate which may be worked up with the ammonium nitrate solution withdrawn from the process to produce a mixed fertilizer consisting of calcium carbonate and ammonium nitrate. According to the Provisional Specification, the lime may be precipitated by means of alkali metal sulphates or mixtures thereof instead of ammonium sulphate; when employing potassium sulphate, it is preferable to separate potassium nitrate from the acid solution before the treatment with ammonia. Examples are given.