Structure of the extracted complex in the Ni(II)-LIX84I system and the effect of D2EHPA addition

The structure of the Ni(II) complex extracted with the commercial hydroxyoxime, LIX84I, and the effect of adding bis(2-ethylhexyl) phosphoric acid (D2EHPA) to LIX84I on the extraction rate and the coordination of Ni(II) were investigated by solvent extraction and XAFS methods. The XANES spectrum and the curve fits of the EXAFS spectrum of the Ni-LIX84I complex showed that the complex is four-coordinate square-planar with a 1:2 stoichiometry. In the Ni(II)-D2EHPA-LIX84I system, the coordination geometry changes from square-planar to six-coordinate octahedral with an increase in the D2EHPA concentration. Although the rate of Ni(II) extraction from the model spent electroless nickel plating bath with LIX84I is significantly accelerated by adding a small amount of D2EHPA ([LIX84I]: 0.5 M, [D2EHPA]: 0.05 M), most of the Ni(II) complexes extracted with this organic solution remain square-planar. This indicates that the increase in the extraction rate does not depend on the change in the coordination structure of the extracted complex.