Equilibrium data for the solvent extraction of nickel from amraoniacal solutions by LIX 64N (10 vol%) dissolved in kerosene (15% aromatic content) are reported. The effect of NH3/aq) concentration, LIX 64N concentration, pH and temperature are shown. The stoichiometry of the Ni-active oxime in LIX 64N complex was ascertained by spectrophotometry studies. A mathematical mechanistic model was developed for the prediction of extraction distribution coefficients as a function of pH. The model predicts more accurate results at high pH values, as could be expected taking into consideration the assumptions made in developing the model.