Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 5Operational dataSee description.ApplicabilityFor specific applications, e.g. for feed- or food phosphates or for pharmaceutical applications, ause of this technique could be possibly recommended [50, German UBA, 2002].For separation of arsenic, an Na 2 S solution is added to the crude acid, and the precipitatedarsenic sulphide is removed by filtration.The separation of cadmium by means of a complexing agent such as alkyldithiophosphoric acidalkyl ester can also be classified as a precipitation reaction because the precipitated cadmiumcomplex is separated in solid form either directly or after addition of a filter aid or absorbent.Such a process is operated on a commercial scale by Tessenderlo Chemie, Belgium.Further purification of wet phosphoric acid by precipitation of cationic impurities, especially Fe,Al, Mg, and Ca, is possible by neutralising the acid with caustic soda. The precipitated metalphosphates are filtered under pressure from the resulting sodium phosphate solution, whichcontains 18 – 20 % P 2 O 5 . In order to decrease P 2 O 5 losses in the filter cake from >10 % to