Abstract: The kinetics of antisynergic extraction of cadmium with D2EHDTPA（di-(2-ethylhexyl)-dithiophosp-horic acid） -TOA（trioctylamine） under the condition of interfacial reaction controlling model was investigated by using an improved constant interfacial area stirred cell. The extraction course was composed of several interphase transfer processes (transfer between bulk phase and interfacial phase (or boundary phase)) and several chemical reactions. The extraction rate equation was : r=1.42*10^-7[Cd²⁺]^0.42[BHA]^0.47/[B]^0.85[H⁺]^0.21 （mol•m^-2•s^-1） The interfacial concentration was associated with the bulk concentration by using Freundlich adsorption equation. The concentration exponents in the extraction rate equation were decided by the two factors of the interfacial chemical reactions and the interphase transfer processes.The physical meaning of the fractional reaction order in the rate equation was analyzed. The bigger the Freundlich power n of a reactant, the more the repulsion exerted by the interfacial layer. The apparent extraction activation energy E=44.2 kJ•mol－1,the extraction enthalpy ΔH=72.9 kJ•mol－1. The inconsistency in extraction mechanism due to different interface models was also discussed.

Key words: Rate equation, Dynamics, Interphase transfer, Thio-substituted organophosphoric acid, Antisynergic extraction