Highly Selective Separation of Cs+ from Brines Using an Electroactive Layered Composite of Vanadosilicate

Green and sustainable separation and recovery of cesium ion (Cs+) have been an important topic in terms of stable supply of this strategic element in recent decades. In this study, to the best of our knowledge, layered vanadosilicate composite was prepared and employed for highly selective separation of Cs+ using an electrochemically controlled process for the first time. The effects of applied voltage, desorption electrolyte, and ion concentration in the Cs+ isolation process were thoroughly investigated. Our results demonstrate that the adsorption and desorption of Cs+ on the electrode can be easily controlled via the redox reactions of vanadium and the efficiency was significantly improved, exhibiting the increase in adsorption capacity from 12.7 to 50.3 mg g–1, while the desorption ratio reached 95% in the presence of an electric field. A good-to-excellent selectivity of Cs+ over K+, Ca2+, and Mg2+ was observed, showing that the separation factors of Cs+/K+, Cs+/Ca2+, and Cs+/Mg2+ are 11.7, 28.9, and 181.4, respectively. Cyclic test shows that the vanadosilicate-coated electrode was stable, which indicates that it can be continuously used to achieve the separation and enrichment of Cs+ in brines. Raman and X-ray photoelectron spectroscopy results revealed that the Cs+ adsorption was achieved by coupling ion-exchange reactions between Cs+ and Na+ and electrochemical reactions (the redox reaction between V3+ and V4+), and the high adsorption capacity was achieved due to the strong binding affinity of Cs+ toward oxygen donors. We anticipate that our findings may point a new way to the green and sustainable separation and enrichment of Cs+ or other trace strategic metals from brines using vanadium-based materials in an electrochemically controlled process.