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

Abstract

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.

Electrochemically Selective Separation of Cesium Ion Using a Silicomolybdate Doped Polyaniline Composite

“…The cyclic voltammetry curve is an electrochemical experimental method, which can be used to investigate the electrochemical behavior of electrode materials under different potentials. ,− , In the cyclic voltammetry experiment, the electrode material is placed in the electrolytic cell, and the current response of the electrode material is collected by changing the potential of the working electrode. With the change of potential, a series of peaks and valleys appear on the cyclic voltammetry curve, reflecting the electrochemical reaction process of the electrode material.…”

“…The adsorption time is 1 h, and the voltage is −0.2 V. The adsorption isotherm curve shows the relationship between the concentration of Cs + in the solution and the Cs + adsorption capacity of the electrode in the adsorption equilibrium state at 25 °C. As shown in Figure , the adsorption capacity and equilibrium concentration were fitted by three isotherm models. ,− The Langmuir–Freundlich model is a versatile isotherm expression that integrates characteristics of the Langmuir and Freundlich models. In addition to accepting the homogeneous surface in Langmuir model, it also considers the heterogeneous active sites and the interaction between adsorbed molecules, which compensates for the shortcomings of the single Langmuir or Freundlich model. − ,, The parameters of three isotherm models are listed in Table S3.…”

“…Figure shows the spectral information on full elements and detailed single element, clearly revealing the chemical state of the element during the capture and release of Cs + on the electrode. In particular, the strong peaks of Cs 3d 5/2 and Cs 3d 3/2 at 725 and 739 eV can be observed in Cs + loaded SiMo 12 –PANI-2 composites (Figures a and b) . The appearance of the Cs 3d peak indicates that Cs + is successfully captured by the SiMo 12 –PANI-2 electrode.…”

“…Although the utilization of potassium and magnesium resources in salt lake brine is well developed, the recovery of low concentration cesium resources is still in its infancy. The concentration of Cs + in brines is relatively low (below 20 mg·L –1 ), while the concentration of competing ions is relatively high (K + > 2 g·L –1 ; Mg 2+ > 20 g·L –1 ; Ca 2+ > 300 mg·L –1 ) . The extraction process requires a large amount of brine and energy, resulting in high costs and energy consumption.…”

“…Electrochemically controlled adsorption and desorption processes have offered an attractive platform due to their modularity and the minimization of secondary pollution. The main feature of these systems is not only their high selectivity from adsorption and ion exchange but also their rapid electron transfer and redox processes, which can reversibly capture and release target ions by changing the potential and direction of the electric field. ,− At present, the interest of researchers mainly focused on Prussian blue and its analogues ,,− in electrochemical separation of Cs + . However, when the iron element in Prussian blue changes valence state under electrochemical conditions, it will break the bond, resulting in poor electrochemical stability of the material.…”