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

The extraction of nickel(II) from various aqueous solutions by 2-ethylhexan al oxime (EHO) in dodecane has been studied as a function of total concentr ations 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 o n 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 as sociation degrees is very important when EHO is used as an extracting reage nt. The EHO aggregation numbers have been determined by the VPO method (Vap our 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, dimer s and trimers. The formation constants of these aggregates have been estima ted by numerical analysis.