PURIFYING METHOD OF WET PROCESS PHOSPHORIC ACID

摘要

Abstract of the DisclosureIt is known to prepare phosphoric acid from the acidic leaching ofphosphate bearing minerals. Such acids generally contain a high fluorinecontent and thus are unsuitable for use in the food industry. The presentinvention seeks to overcome this drawback by providing a process for purifyingand defluorinating an impure phosphoric acid produced by a sulphuric acidtreatment of a phosphate-bearing rock which comprises the counter-currentextraction of the impure aqueous phosphoric acid solution with an organicsolvent having a low miscibility with water, in the presence of concentratedsulfuric acid, washing of the resulting phosphoric acid organic phase withwater or purified phosphoric acid and counter-current re-extracting thephosphoric acid contained in the organic phase with water, separating theresulting dilute aqueous solution of decationised and partially defluorinatedphosphoric acid, and treating said solution with steam, hot gas, or a mixturethereof to obtain a concentrated and defluorinated aqueous phosphoric acidsolution in which the F/P2O5 ratio by weight is lower than 10 ppm.