Ion-Exchange Considerations in Dilute Chemical Decontamination Processes Operated in the Regenerative Mode

Dilute chemical decontamination processes use ion-exchange resins for collecting the metal ions, radioactive contaminants, and formulation chemicals. In decontamination processes operated in the regenerative mode, the ion-exchange resin is also used for regenerating the spent formulation. Normally, the cation exchange resin is used during the regeneration stage of the process. During decontamination, the chemical formulation dissolves the contaminated metal oxide film from the system surfaces. The complexants present in the formulation form complexes with the metal ions thus released and keep them in solution. An investigation has been carried out to study the ion-exchange reaction among the complexants, the metal complexes of interest to decontamination, and the cation exchange resin. Sorption behavior of ethylenediaminetetraacetic acid on the cation exchange resin in a heavy water medium as a function of pH was studied, and the observed sorption values were compared with normal water sorption and explanations offered to account for the difference. Simultaneous pickup of different metal ions on the cation exchange resin may result in elution of one or more metal ions by another ion. Results of elution experiments are discussed. An attempt to correlate the stability of the various metal complex species formed in solution and the apparent capacity of the cation exchange resin to the metal ion is made. The effect of pH, temperature, concentrations of metal ion, and the complexants in controlling the metal ion pickup on the cation exchange resin is explained. The use of strong- and weak-base anion exchange resins in decontamination is explained.