Mineral-driven persulfate activation: the role of recycled concrete alkalinity in oxidative water treatment

Abstract

The dissolution of concrete—a prevalent anthropogenic material—generates hyperalkaline, Ca-rich leachates that may influence redox processes in subsurface environments. The knowledge of these geochemical processes serves as theoretical framework for the application of recycling concrete material to circular economy systems, providing sustainable alternatives to the concerning issue of the construction waste management while positively acting on specific environmental settings. This study investigates the potential of recycled concrete as a long-term alkaline activator for sodium persulfate in In Situ Chemical Oxidation groundwater treatments, with a focus on application in groundwater-recharge interception trenches in the vadose zone. A laboratory-scale study was conducted using flow-through columns filled with crushed recycled concrete, which was exposed to contaminated groundwater. The research assessed (i) the ability of concrete to generate and maintain alkaline conditions for persulfate activation, (ii) its mineralogical composition to determine reactivity and surface passivation, and (iii) chemical changes occurring upon persulfate addition at two different dosages. Results showed that recycled concrete effectively maintained high pH and buffered the system after persulfate injection, enabling efficient activation of the oxidant and substantial degradation of dissolved organic carbon. The system was controlled by the dissolution of concrete aggregates and cement phase together with the carbonation and (re)precipitation of new phases. The role of calcium and aluminium/magnesium silicate hydrates was proven to be crucial for the stability of the concrete microstructure and for maintaining the alkalinity. These findings demonstrate the dual role of recycled concrete for providing long-term alkaline activation of persulfate and mitigating clogging risks, supporting is practical use in groundwater remediation strategies promoting circular economy principles. Furthermore, these findings mirror processes observed in different hyperalkaline systems (e.g., radioactive waste repositories, CO₂ storage) where mineral-driven redox reactions control contaminant fate and/or carbon sequestration.