Investigating the electrosorption selectivity of mesoporous carbon electrodes for sulfate from mining wastewater in membrane capacitive deionization

Sulfate contamination is a common problem in mining wastewater. We evaluated the selectivity of a dual-activated mesoporous carbon (DPC) electrode for sulfate in simulated solutions and actual mining wastewater due to the complex composition of actual mining wastewater. Our findings showed that the normalized equivalent electrosorption capacity of membrane capacitive deionization (MCDI) in equimolar ternary solution exhibited the following order: SO₄^2- (0.42 mmol/g) > NO₃^- (0.31 mmol^/g) > Cl^- (0.03 mmol/g), which was related to the DCP and ionic properties. Density-functional theory (DFT) calculations indicated that the superior selectivity of the DPC electrode for SO₄^2- was also associated with the higher binding energies between the oxidized functional groups and SO₄^2-. DPC-based MCDI effectively removed high concentrations of sulfate and common heavy metals from actual mining wastewater. Moreover, it exhibited excellent selectivity towards SO₄^2-, demonstrating the feasibility of DPC electrode-based MCDI for treatment of real mining wastewater.