Rotating stabilised cell: a new tool for the investigation of interfacial extraction kinetics between liquid phases

New experiments performed with an improved version of the rotating stabilised cell are presented. In this technique the aqueous phase is immobilised: it is found that a gel of polyacrylamide is a good stabilising medium for this purpose. The gel is placed in a cylindrical cell of small dimensions which can be set to rotate. A pure diffusion of the species to be extracted occurs in the aqueous phase. A flat interface is created for the contact with the organic extractant solution. A rotating-disc flow is promoted in this phase, which permits the control of the diffusive layer. The system investigated is the cobalt(II) ion at the interface water (+ buffer solution and supporting electrolyte)/DEHPA [bis(2-ethylhexyl)hydrogenphosphate] 0.2 mol dm–3 in dodecane, for two values of the pH of the aqueous phase: pH 3 and pH 5. A mathematical expression is derived for the amount of matter transferred, and the validity of the formula is examined mathematically. The influence of the rotation speed of the cell and the influence of its length are studied in the case where the pH is 3. The values of the aqueous-toward-organic rate constants found at pH 3 and pH 5 are in reasonable agreement with the results of other workers.