The EIX Process for Radioactive Waste Treatment

Summary

In Electrochemical Ion-exchange (EIX), the absorption and elution behaviour of ion-exchangers incorporated into an electrode is controlled by an external potential. A negative potential applied to a weak acid cation exchanger electrode causes cations to be absorbed progressively to low concentrations as the feed passes up through the cell — thus giving large decontamination factors, even at high cation loadings. On polarity reversal, the absorbed ions can be eluted into a limited volume to give a concentrated product for subsequent immobilization. By making multiple and complete use of ion-exchange capacity in this way, large volume reduction factors can be achieved for minimal energy expenditure. Both anion and cation systems are available — based on either organic or Inorganic absorbers, although the latter have a higher radiation tolerance.

A number of genuine waste streams have been treated successfully in bench-top trials — including the Harwell site LLW, MTR pond water and PWR wastes — reducing residual activity to low levels at relatively high throughputs. The system has also been scaled-up successfully on a number of these streams, initially by a factor of 11 to a single cell of 0.1 m³/h nominal throughput, and more recently in a multi-modular unit by a further factors of 5.