GB355637A - Improvements in or relating to the manufacture and production of fertilizers - Google Patents

Abstract

In the production of fertilizers by reacting phosphate rock with nitric acid and treating the decomposed phosphate with ammonia, the gases evolved during the acid treatment, comprising carbon dioxide, fluorine compounds, and nitrogen oxides, are used, wholly or in part, in conjunction with ammonia during the subsequent treatment. 3-6 mols. nitric acid may be employed for each mol. of phosphoric acid in the rock, together with sufficient to decompose impurities present, such as calcium carbonate and fluoride. For instance the intermediate product may contain water-soluble calcium phosphate, calcium nitrate and some free acid, and it may be treated with sufficient ammonia to neutralize the free acid and to convert part or all of the phosphate to the citrate-soluble form. All or part of the calcium nitrate present may be converted to ammonium nitrate, or enough ammonia may even be used to yield a product containing mono-or di-ammonium phosphate and some reverted tricalcium phosphate. Anhydrous gaseous or liquid ammonia is preferably employed, but aqueous ammonia may be used, and partial ammoniation may be effected before the introduction of the previously evolved gases. The invention is particularly applicable to the treatment of low-grade phosphates containing more than one mol. of calcium carbonate and fluoride taken together to each mol. of phosphoric acid, but it may be applied to high grade materials, in which case additional carbon dioxide may be added to the evolved gases. Fluorine compounds may be separated from the gases before their return to the process.ALSO:In the production of fertilizers by reacting phosphate rock with nitric acid and treating the decomposed phosphate with ammonia, the gases evolved during the acid treatment, comprising carbon dioxide, fluorine compounds, and nitrogen oxides, are used, wholly or in part, in conjunction with ammonia during the subsequent treatment. 3-6 mols. nitric acid may be employed for each mol. of phosphoric acid in the rock, together with sufficient to decompose impurities present such as calcium carbonate and fluoride. For instance the intermediate product may contain water-soluble calcium phosphate, calcium nitrate and some free acid, and it may be treated with sufficient ammonia to neutralize the free acid and to convert part or all of the phosphate to the citrate-soluble form. All or part of the calcium nitrate present may be converted to ammonium nitrate, or enough ammonia may even be used to yield a product containing mono, or di-ammonium phosphate and some reverted tricalcium phosphate. Anhydrous gaseous or liquid ammonia is preferably used, but aqueous ammonia may be employed, and partial ammoniation may be effected before the introduction of the previously evolved gases. The invention is particularly applicable to the treatment of low grade phosphates containing more than one mol. of calcium carbonate and fluoride taken together to each mol. of phosphoric acid, but it may be applied to high grade materials, in which case additional carbon dioxide may be added to the evolved gases. Fluorine compounds may be separated from the gases before their return to the process.