PURIFYING AND DEFLUORINATING IMPURE PHOSPHORIC ACID

摘要

It is known to prepare phosphoric acid from the acidic leaching of phosphate bearing minerals. Such acids generally contain a high fluorine content and thus are unsuitable for use in the food industry. The present invention seeks to overcome this drawback by providing a process for purifying and defluorinating an impure phosphoric acid produced by a sulphuric acid treatment of a phosphate-bearing rock which comprises the counter-current extraction of the impure aqueous phosphoric acid solution with an organic solvent having a low miscibility with water, in the presence of concentrated sulfuric acid, washing of the resulting phosphoric acid organic phase with water or purified phosphoric acid and counter-current re-extracting the phosphoric acid contained in the organic phase with water, separating the resulting dilute aqueous solution of decationised and partially defluorinated phosphoric acid, and treating said solution with steam, hot gas, or a mixture thereof to obtain a concentrated and defluorinated aqueous phosphoric acid solution in which the F/P2O5 ratio by weight is lower than 10 ppm.