Solvent extraction of nickel(II) by mixture of 2-ethylhexanal oxime and bis(2-ethylhexyl) phosphoric acid

The extraction of nickel(II) from acidic aqueous solutions using a mixture of 2-ethylhexanal oxime (EHO) and bis(2-ethylhexyl) phosphoric acid (D(2)EHPA) in dodecane has been investigated as a function of total concentrations of each extractant, metal and protons. The aqueous salt concentration is proved to have no significant effect for both ammonium. nitrate and chloride. The extracted organic complex is then Ni(Ox)(2)(HOx)(2)(HA)(2) or Ni(HOx)(4)A(2), where HA denotes the organo-phosphoric acid and HOx the oxime. A complementary isomolecular study has been achieved to confirm this stoichiometry. As aggregation plays a crucial role in extraction phenomenon, Vapor Pressure Osmometry (VPO) measurements have been carried out in order to determine the aggregation numbers for either the separate extractants or their mixtures. The bis(2-ethylhexyl) phosphoric acid is mainly under dimer and trimer forms, while no mixed aggregation is observed.