REVERSIBLE EXTRACTION OF IONIC SPECIES USING ELECTROCHEMICALLY ASSISTED ION-EXCHANGE .1. COBALT(II) USING ALPHA-ZIRCONIUM HYDROGEN PHOSPHATE

In electrochemically assisted ion exchange (EIX), a water splitting reaction is used to promote the ion-exchange properties of materials which are incorporated into electrodes. Thus cobalt(II) may be extracted using alpha-zirconium hydrogen phosphate (ZrP) in a matrix of an unreactive polymer in which a platinised titanium electrode is embedded. Although ZrP is an inefficient ion-exchanger under normal (non-assisted) conditions, EIX promotes the cation exchange behaviour by generation of hydroxyl ions (OH-) at the cathode. There was no observable precipitation of cobalt(II) hydroxide and no plating-out of the cobalt. The process of exchange proceeds entirely by an ion exchange mechanism. There is some base hydrolysis of the ZrP in the vicinity of the cathode, particularly in the first few cycles. Elution may be achieved by reversal of the applied electrical potential in conjunction with a solution pH of less than 2.3. For comparable electrodes, the rate of exchange, using EIX, is significantly greater and the final concentration lower, than is achieved by the use of normal ion exchange.