A sustainable flow electrode capacitive deionization approach for efficient decontamination and uranium recovery from strongly acidic mining wastewater

The effective removal and recovery of uranium (U) from mining wastewater is of vital importance for environmental protection and the sustainable development of nuclear power industry. In this study, we applied flow electrode capacitive deionization (FCDI) to the treatment of uranium-contaminated groundwater generated after acid in-situ leaching (AISL). While FCDI has been previously explored for nutrient and heavy metal removal, as well as preliminary uranium extraction, this work uniquely demonstrates its effectiveness in strongly acidic, sulfate-rich mining wastewater, achieving >95 % uranium removal and >80 % recovery under optimal conditions. Theoretical calculations and experimental results reveal that U and coexisting ions in feedwater migrate rapidly to the cathode and anode during charging. UO₂²⁺ is electrochemically reduced to insoluble UO₂ on the carbon particles in the cathode, while UO₂(SO₄)₂²⁻ is decomposed into UO₂(SO₄) or UO₂²⁺ and SO₄²⁻ in the anode. After polarity reversal, the coexisting ions quickly transport into the spacer, while uranium is trapped in the cathode and anode, enabling selective uranium recovery. Long-term cycling tests using real mining wastewater confirms the FCDI system's high stability and material durability over 12 charging-discharging cycles. This study demonstrates FCDI as a promising technology for simultaneous uranium remediation and resource recovery from strongly acidic groundwater.