A chemically tailored capacitive deionization system for the enhanced removal of cesium from process water

Abstract

A capacitive deionization (CDI) electrode comprising ethylenediamine triacetic acid (EDTA) and 2D MXene (EDTA-MXene) is fabricated to separate Cs+ from strongly acidic process water. The method provides new direction for an advanced aqueous recycle process to separate fission products from spent fuel liquor. Grafting EDTA on MXene has no detrimental effect on its structure but does diversify the modes of ion interaction and increase the number of binding sites. The composite CDI electrode has a Cs+ adsorption capacity of 2.07 mmol g−1 at 1.2 V with 97.3% removal efficiency within 15 min. Step-wise adsorption and desorption cycling of the electrode highlights the chemisorption effect of EDTA which immobilizes the ions as the applied voltage is lowered, although almost all ions can be stripped by reversing the voltage to −1.4 V and without the need for chemical treatment. The EDTA-MXene electrode demonstrates outstanding cyclic performance with a capacity retention of >80% after 320 cycles. Furthermore, the electrode maintains its performance in strongly acidic solution, removing 0.66 mmol g−1 Cs+ at 1.2 V, as well as being stable after immersing in 3 mol L−1 HNO3 for 7 days. Through continuous cycling it is possible to enrich the Cs+ into a highly concentrated solution for element recovery or safe disposal. The EDTA-MXene material is robust and maintains good performance in harsh chemical environments, levering its multiple binding sites to successfully isolate Cs+ from strongly acidic solutions and in the presence of competing ions, Sr2+ and Ce(IV).