GB464370A - Improvements in and relating to processes for the purification of crude phosphoric acid - Google Patents

Abstract

Pure phosphoric acid is obtained from an aqueous solution of the crude acid, which may also contain other acids such as sulphuric acid, by dissolving the crude aqueous acid in a water-miscible organic solvent in the presence of small quantities of an alkali metal or ammonium compound, freeing the resulting solution from precipitated impurities and removing the solvent from the phosphoric acid. Suitable organic solvents are 92 per cent ethyl alcohol, methylated spirit or acetone. Suitable alkali metal or ammonium compounds are sulphates, oxalates, phosphates, carbonates, chlorides or nitrates of potassium, sodium or ammonium, alkaline lyes or combinations of the above compounds. The above additions may be introduced during the preparation of the crude phosphoric acid from crude phosphate or its decomposition products or as a concentrated solution or in a finely pulverized state before or after the addition of the solvent. The precipitated residue may be treated with water, the impurities remaining undissolved or being converted into insoluble basic salts while the alkaline compounds and the phosphoric acid are dissolved. The resulting solution may then be used for the repeated purification of phosphoric acid. The phosphoric acid after the removal of the solvent by distillation may be further purified by treatment with activated carbon.