Abstract: The extraction of Ni(Ⅱ) from 0.100 mol/L CH₃COO(H,Na) with HDEHP in different diluents, such as benzene,toluene,n-hexane, cyclohexane, CCl₄ and chloroform, has been studied. The species formed in the extraction and the extraction machanism have been examined by means of IR spectra. It shows that the complex formed in chloroform is different from that formed in other diluents. The effect of diluents is discussed. The extraction equilibrium constants and the extraction distribution are correlated with the physical constants and(or) experimental parameters of diluents, respectively. The effect of temperature has also been investigated, and the thermodynamic constants △G⁰, △H⁰ and △S⁰ at 298 K are obtained.

Key words: HDEHP, diluent, extraction equilibrium