Abstract: The extraction behavior of Co(Ⅱ) and Ni(Ⅱ) by a series of dialkylphosphoric acids,mono-esters of alkylphosphonic acids, and dialkylphosphini? acids was investigated. Thepolar and the steric effects of the substituents in extractant molecule on the extraction pro-perties were studied by means of a correlation analysis method. The extractability of Ni ismore dependent on the extractants' structure than that of Co, As the number of C-P bondsand the steric hindrance of the substituents increase, consequently, their separation abilityincreases, Ni extraction decreases more significantly than Co. This difference of Co andNi in extraction is explained in terms of the steric configuration of their complexes formedduring the extraction.

Key words: Acidic organophosphorus extractant, Co(Ⅱ), Ni(Ⅱ), Extraction