STUDIES OF THE CE(III)/CE(IV) COUPLE IN MULTIPHASE SYSTEMS CONTAINING A PHASE-TRANSFER REAGENT .1. CONDITIONS FOR THE EXTRACTION OF CE(IV) AND ELECTRODE-KINETICS

The factors influencing the transfer of Ce(IV) from aqueous solutions to organic solvents using either tetrabutylammonium ion or tributylphosphate as the extractant are investigated. It is shown that extraction is efficient from acidic nitrate solutions but that other anions, particularly sulphate, decrease the extent of transfer; in contrast, Ce(III) always extracts only very poorly, if at all. Cyclic voltammetry has been used to study the Ce(III)/Ce(IV) couple. In acidic aqueous nitrate, the formal potential is independent of both proton and nitrate concentrations while the standard rate constant increases with added proton but is independent of nitrate concentration. Added sulphate causes a shift in formal potential to less positive values and a marked deceleration in the rate of electron transfer.