Comparative study of direct and indirect aqueous mineral carbonation of construction and demolition waste fines for CO2 sequestration

Abstract

Sustainable development prioritizes waste utilization to mitigate environmental impacts through recycling and reuse. In construction and demolition waste (C&DW) recycling, the recovery of recycled concrete aggregate generates C&DW fines. These fines contain significant calcium (Ca), making them potential feedstock for CO2 sequestration through accelerated mineral carbonation processes. This approach offers a promising pathway for reducing CO2 emissions from the cement industry by utilizing alkaline waste to form thermodynamically stable carbonates. This study compares the effectiveness of direct and indirect aqueous mineral carbonation in sequestering CO2 using classified C&DW fines. Laboratory experiments assessed Ca extraction using borehole water (BHW) and acid mine drainage (AMD) as leaching agents, along with optimization of the solid-to-liquid (S/ L) ratio for carbonation. Analysis of raw C&DW fines, leached residue, leachate, and the resulting solid carbonation product was performed using XRD, XRF, TGA, BET/BJH, PSD, and ICP-OES techniques. A 1:10 S/L ratio was optimal for Ca extraction and subsequent carbonation. BHW leached ~328 mg-Ca/L-BHW, significantly higher than AMD (85 mg-Ca/L-AMD). High concentration of SO2−4 in AMD reacted with Ca to form gypsum, limiting Ca leaching into the solution. Thus, BHW was used in subsequent carbonation experiments. Direct aqueous carbonation achieved a total CO2 uptake of 52.8 g-CO2/kg-C&DW fines, whereas indirect aqueous carbonation captured 10.5 g-CO2/kg-C&DW fines. This research highlights the benefit of repurposing C&DW as low-cost material for direct CO2 capture. Moreover, the potential substitution of BHW with polluted waste streams like AMD underscores an integrated approach to waste valorization and CO2 mitigation, particularly in water-scarce regions.