Process for the removal of heavy metals from a phosphoric acid containing composition using a flocculating agent

A process for the removal of heavy metals from a phosphoric acid containing composition, comprising the steps of

• (a) providing a phosphoric acid containing composition comprising dissolved heavy metals;
• (b) precipitating the dissolved heavy metals by adding a heavy metal precipitating agent to the composition of step (a), at a pH of 1.6 to 2.2 measured after a 13-fold dilution by volume using water, thereby obtaining a heavy metal precipitate in a phosphoric acid containing composition, wherein the heavy metal precipitating agent comprises a diorgano-dithiophosphinic acid or an alkali metal or ammonia salt thereof, represented by Formula 1
• wherein R is a linear or branched hydrocarbon group selected from alkyl, aryl, alkylaryl, or aralkyl, and wherein the hydrocarbon group contains 3 to 20 carbon atoms, and M is H, alkali metal or ammonia;
• (c) adding a first flocculating agent having a molecular weight of 4×106 Dalton to 8×106 Dalton, to the composition obtained in step (b), wherein said first flocculating agent is a cationic polymer wherein 20% to 80% of the moieties making up the cationic polymer are cationic charged moieties, an anionic polymer wherein 10% to 50% of the moieties making up the anionic polymer are anionic charged moieties, or a mixture thereof, thereby obtaining agglomerates comprising the heavy metal precipitate in a phosphoric acid containing composition;
• and
• (d) separating the agglomerates comprising the heavy metal precipitate from the phosphoric acid containing composition, and wherein
• the phosphoric acid containing composition is an acidic aqueous composition comprising from 6-21 wt % nitric acid, from 25 to 33 wt % phosphoric acid, from 3.5 to 5 wt % calcium and dissolved heavy metals, where the wt % is based on the total weight of the composition.