Process for the removal of heavy metals from 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 to the composition of step (a), 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;
• wherein the precipitating step (b) is performed at a pH of 1.6 to 2.0 (measured after a 13-fold dilution), wherein
• step (b) comprises the steps of:
• (b1) precipitating the dissolved heavy metals by adding the heavy metal precipitating agent to the composition of step (a), thereby obtaining a heavy metal precipitate in a phosphoric acid containing composition;
• and
• (b2) adding a second flocculating agent to the composition obtained in step (b1), thereby obtaining agglomerates comprising the heavy metal precipitate, wherein said second flocculating agent is an anionic polymer, a cationic polymer or a mixture thereof that is suitable for the agglomeration and flocculation of the composition obtained in step (b1),
• and wherein the heavy metals are selected from cadmium, mercury, zinc, arsenic, manganese and/or lead.