Selective cesium extraction from highly saline solution using hybrid capacitive deionization with zinc-doped manganese hexacyanoferrate electrode

Abstract

Recently, hybrid capacitive deionization (HCDI) has garnered significant attention for its potential in the selective extraction of cesium (Cs) from radioactive wastewater and salt lakes, which is crucial for resolving the supply-demand imbalance of cesium resources and eliminating radioactive contamination. However, developing HCDI electrodes capable of effectively separating and extracting Cs remains a significant challenge. In this work, we proposed an innovative strategy involving the doping of inactive metal ions to develop zinc-doped manganese hexacyanoferrate (ZMFC) as an HCDI cathode. This approach leveraged the synergistic effects of ion sieving of three-dimensional lattice and zinc doping to regulate electrochemical activity, enabling the selective electrochemical extraction of Cs⁺ ions from highly saline solutions. The optimized ZMFC-0.1 electrodes exhibited a maximum electrosorption capacity of 299.9 mg g^–1 in a 400 mg L^–1 Cs⁺ ion solution and maintained a high-capacity retention rate of 80.1 % after 50 consecutive absorption-desorption cycles in a 200 mg L^–1 Cs⁺ ion solution. Moreover, ZMFC-0.1 showed a high selectivity coefficient of 27.4 at a Cs⁺/Na⁺ molar ratio of 1:40. Density functional theory (DFT) simulation revealed that manganese hexacyanoferrate (MnHCF) retains high stability and electrochemical activity following zinc atom doping. In-situ X-ray diffraction and theoretical calculations provided deeper insights into the mechanisms underlying reversible capacitive adsorption and selective Cs⁺ ion separation. The effectiveness of cesium selective extraction from brine in Xizang suggests that the ZMFC-0.1 electrodes hold significant promise for cesium recovery from salt lakes. This work presents a promising strategy for the electrochemical extraction of cesium from radioactive wastewater and salt lakes.