Localized electro-dissolution of wollastonite boosts heavy metal extraction from acidic wastewater

Industrial acidic wastewater laden with hazardous heavy metals (e.g., Cu, Cd, Ni, Zn) presents critical global environmental challenges, posing severe threats to aquatic ecosystems and human health. Although conventional lime-based neutralization is widely employed, it is severely constrained by high carbon emissions, energy-intensive production, and substantial operational costs. In contrast, wollastonite (CaSiO₃), a natural mineral, offers a promising low-carbon alternative for remediation, yet its remediation efficacy is frequently bottlenecked by insufficient pH elevation and rapid surface passivation caused by secondary mineral coatings. To overcome these limitations, we developed a novel localized electrochemical system that spatially decouples mineral dissolution at the anode from metal precipitation at the cathode. By strategically packing wollastonite within the anode region, anode-generated protons actively accelerate mineral dissolution and inhibit passivation layers by maintaining an acidic condition, while the cathode generates a localized high-pH microenvironment to facilitate heavy metal immobilization. Experimental results demonstrated that this synergistic approach achieved near-complete removal (∼100.0%) of multiple target metals across varying acidic matrices with low energy consumption (<29.6 kW·h/kg metals). Solid characterization revealed that removal occurred through three synergistic mechanisms: cathodic electro-reduction, localized high-pH precipitation, and bulk solution pH-mediated precipitation. Crucially, the anodic acidity successfully prevented mineral passivation, while the effluent's persistent alkalinity enabled the sequestration of approximately 140.8 g/m³ of atmospheric CO₂. This integrated process yields purified water, recovered valuable metals, and anodically purified silica, transforming hazardous waste streams into economic value.