Process for purifying phosphoric acid

A method for purifying crude wet-process phosphoric acid containing at least one of vanadium or chromium as anionic metallic complexes which comprises, in combination:

• (A) treating crude wet-process phosphoric acid with sufficient amounts of a sulfide or metallic iron in aqueous medium to convert said anionic complexes of high oxidation levels to cationic forms of lower oxidation levels;
• (B) extracting the treated crude wet-process phosphoric acid of Step (A) with a water-immiscible solvent selected from the group consisting of monoalcohols and ethers having four to eight carbon atoms or mixtures thereof at a temperature of 20.degree. to 60.degree. C.;
• (c) removing cationic impurities from the treated medium of Step (B) by separating phosphoric acid containing anionic impurities in the water-immiscible solvent;
• (D) re-extracting the separated water-immiscible solvent of Step (C) at a temperature of 20.degree. to 60.degree. C. with water to permit the phosphoric acid and anionic impurities to be reextracted into a second aqueous phase;
• (E) contacting the second aqueous phase with a water-immiscible alkaline liquid medium having a poor dissolving power for phosphoric acid and containing from about 5% to 100% of a secondary or tertiary amine having from 18 to 60 carbon atoms so that the anionic impurities are transferred to said alkaline liquid medium;
• and
• (F) physically separating the second aqueous phase containing purified phosphoric acid.