Solvent extraction of nickel(II) by 2-ethylhexanal oxime from various aqueous solutions

The extraction of nickel(II) from various aqueous solutions by 2-ethylhexanal oxime (EHO) in dodecane has been studied as a function of total concentrations of extractant, metal and salts and of the equilibrium pH. In the absence of salts, as well as in the presence of ammonium and sodium nitrates, the extracted complex, is: Ni(EHO)(5)(H2O). In the complexing chloride medium, two different species exist, depending on acidity: for pH lower than 4, Ni(EHO)(3) Cl-2(H2O) and pH above 4, Ni(EHO)(4)Cl(H2O). 2-ethylhexanal oxime forms multimers. In dodecane The knowledge of these association degrees is very important when EHO is used as an extracting reagent. The EHO aggregation numbers have been determined by the VPO method (Vapour Pressure Osmometry) at three temperatures (24, 29 and 34 degreesC) in a wide concentration range (0.03-0.77 mol.kg(-1)). EHO forms monomers, dimers and trimers. The formation constants of these aggregates have been estimated by numerical analysis.