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

Abstract

The dissolution of concrete—a prevalent anthropogenic material—generates hyperalkaline, Ca-rich leachatesthat may influence redox processes in subsurface environments. The knowledge of these geochemical processesserves 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 positivelyacting on specific environmental settings. This study investigates the potential of recycled concrete as a longtermalkaline activator for sodium persulfate in In Situ Chemical Oxidation groundwater treatments, with afocus on application in groundwater-recharge interception trenches in the vadose zone. A laboratory-scale studywas conducted using flow-through columns filled with crushed recycled concrete, which was exposed tocontaminated groundwater. The research assessed (i) the ability of concrete to generate and maintain alkalineconditions for persulfate activation, (ii) its mineralogical composition to determine reactivity and surfacepassivation, and (iii) chemical changes occurring upon persulfate addition at two different dosages. Resultsshowed 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 systemwas 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 tobe crucial for the stability of the concrete microstructure and for maintaining the alkalinity. These findingsdemonstrate the dual role of recycled concrete for providing long-term alkaline activation of persulfate andmitigating clogging risks, supporting is practical use in groundwater remediation strategies promoting circulareconomy 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.