Sequestration capacity of bio-based ashes and influence of carbonation on the leaching behavior depending on their mineralogical composition

Mineral CO 2 sequestration is a promising carbon capture and storage approach based on the chemical reaction of CO 2 with alkaline materials containing Ca- and Mg-rich (hydr)oxides and silicates. This results in the formation of relatively insoluble and storable carbonates. This study investigates six ashes of different origins and chemical compositions to assess their CO 2 sequestration potential and leaching behavior, offering insights into their environmental impact and potential risks. The carbonation experiments were conducted under controlled laboratory conditions and the CO 2 sequestration capacity was quantified using a pressure calcimeter, supported by thermogravimetric analysis. Wood ashes and ash from the co-combustion of biomass from a paper mill showed the highest carbonation potential, with CO 2 sequestration capacities between 344.8 and 432.3 g CO 2 per kg of ash and carbonation efficiencies between 82.4% and 94.4%. In addition to the high sequestration capacity of the ashes, carbonation was found to affect the leaching behavior of the ash in the environment by changing its mineralogical composition. The process consistently reduced pH and generally decreased the leaching of certain trace elements, except for Mo, and Cr. Nevertheless, the reduction in the leachability of several elements suggests a partial environmental benefit of carbonation. The findings highlight the dual functionality of the carbonation: it provides a viable route for the permanent binding of CO 2 and can enhance the stabilization of industrial residues. However, the persistence of metal leaching indicates that its overall effectiveness in mitigating environmental risks associated with residue disposal or reuse remains material-dependent.