Efficient removal of uranium and sulfate in acid contaminated groundwater by flow electrode capacitive deionization

Abstract

In-situ leaching (ISL) causes non-negligible groundwater pollution. It is urgent to remediate the groundwater after ISL activities. In this study, we evaluated the effectiveness of flow electrode capacitive deionization (FCDI) to treat a simulated groundwater, the uranium (U) and SO42− concentration of which are comparable to groundwater in acid in-situ leaching (AISL) uranium mine for the first time. Moreover, the removal mechanism of U and SO42− were investigated in-depth. It is found that the operational mode, applied voltage and initial SO42− concentration significantly affect the removal of U and SO42− by FCDI. The removal efficiency of U and SO42− were above 98 % at 75 min under optimal condition, although U in groundwater mainly existed in the form of uncharged UO2(SO4), followed by UO22+ and UO2(SO4)22−. UO22+ and UO2(SO4)22− in groundwater migrated into the two poles and were quickly absorbed by flow electrode, which promoted the dissociation of UO2(SO4) or complexation of UO2(SO4) with SO42−. In addition, the anion exchange membrane can absorb UO2(SO4) through complexation. These resulted in the efficient removal of U(VI). FCDI can reduce the U and SO42− concentration of the contaminated water (CU = 10 mg L−1, CSO42− = 5 g L−1) to a value lower than the Chinese emission limit (U: 300 μg L−1; SO42−: 250 mg L−1) even after 18 cycles with each cycle operated for 120 min, which informed that FCDI system using activated carbon is of great potential for acidic contaminated water treatment.