The kinetics of solvent extraction of Co2+and Ni2+with three typical acidic organophosphorus extractants

di-2-ethylhexyl phosphoric acid(P204)

ethylhexyl phosphiric acid mono-2-ethylhexyl ester(P507) and di-2

2

4-trimethyl phosphinic acid (Cyanex 272) was compared by using the data determined by the author and from the literatures. The rate of solvent extraction of Co2+was faster than Ni2+. The extraction of nickel was controlled by chemical reaction in the aqueous layer. Cobalt extraction is under a mixed reaction-diffusion regime and its reaction zone is located at the interface and in the aqueous layer

which could be shifted with the change of the reaction conditions. With regard to the reaction

the rate-controlling one might be the exchange of the inner shell coordinate water with the first substituting extractant molecule

which is in agreement with the Eiger-Willkings rule of coordination compound formation in a homogeneous system. The kinetic activity of the extractants depended on the polarity of the phosphonyl group in the molecule of the extractant

and the activity decreased with the substitution of the oxyalkyl groups with the alkyl groups.The polarity of the phosphonyl also predominates over the acidity

surface activity and the dissolution rate of the extractant from the organic phase to the aqueous. In the present research the extraction rates of both Co2+ and Ni2 decreased in the sequence of P204

P507 and Cyanex 272.