The effect of EDTA and citrate on alpha decontamination processes

The results of a study investigating the effect of the complexants EDTA and citrate on the actinide decontamination achieved by precipitation and ultrafiltration treatment processes are presented. A computer simulation study employing the computer code PHREEQE has been used to predict the chemical speciation and solubility of plutonium, americium and neptunium in a waste effluent during its treatment by either a ferric or uranic floc process. Three different concentrations of the complexants were considered. The model's predictions have subsequently been validated by a small number of experimental measurements. It is concluded that the presence of both EDTA and citrate affect the actinide decontamination achieved by precipitation and ultrafiltration processes. The actinides readily form complexes with EDTA and citrate which increase their solubilities in aqueous systems and these complexes appear to be less readily adsorbed onto the flocs than the hydrolysis products that would be present in the absence of the complexants. The extent to which EDTA and citrate complexation takes place depends on the concentration of the complexant present; however, the results indicate that actinide decontamination is still adversely affected at the lowest complexant concentrations (10-6M) considered. (author)