Flocculation studies on freshly precipitated copper ferrocyanide for the removal of cesium from radioactive liquid waste

Flocculation of copper ferrocyanide precipitate, used for the removal of Cs-isotopes from low-level and intermediate-level radioactive liquid waste, has been studied. Application of optimum dosages of flocculants, such as Polyelectrolytes and Fe[sup 3+] ions, is observed to enhance the removal of Cs and aid the separation of solid and liquid phases. Electrophoretic measurements have been used as a tool to determine the optimum dose of ferric ions by finding out the reversal of charge concentration (RCC) for Cu-ferrocyanide, precipitated in effluents of different specific conductances. The optimum requirement of Fe[sup 3+] ions increases with increasing specific conductances of the effluents. Presence of a complexing agent like EDTA affects the removal of Cs and also the separation of phases. The problem can be solved, at least for low concentration of EDTA, by lowering the pH to an optimum value, which has again been determined through electrophoretic measurements. It is inferred that uptake of Fe[sup 3+] ions by Cu-ferrocyanide proceeds through adsorption and ion-exchange with Cu[sup 2+] ions. When Cs[sup +] is present at very low concentration, for example as a radiopollutant, its removal is favored on addition of Fe[sup 3+] as flocculant, but at higher concentrations, the Cs[sup +] ions also partially undergo exchange with the Cu[sup 2+] ions, thus participating in the formation of precipitate. Addition of Fe[sup 3+], then, may not be desirable, as it may exchange with both Cu[sup 2+] and Cs[sup +] ions, releasing them into solution.