Process for the removal of heavy metals from a phosphoric acid containing composition using an ionic polymeric surfactant and use of said surfactant in the precipitation of heavy metals in a phosphoric acid containing composition

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 and a surfactant having a molecular weight of 4×106 Dalton to 8×106 Dalton, to the composition of step (a), at a pH of 1.6 to 2.2, 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;
• and
• (c) separating the heavy metal precipitate from the phosphoric acid containing composition of step (b),
• wherein the surfactant is a cationic polymeric surfactant wherein from 20% to 80% of the moieties making up the cationic polymeric surfactant are cationic charged moieties, an anionic polymeric surfactant wherein from 1% to 10% of the moieties making up the anionic polymeric surfactant are anionic charged moieties, or a mixture thereof, and
• 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, with wt % based on the total weight of the composition.