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Abstract: Mineral CO2 sequestration is a promising carbon capture and storage approach based on the chemical reaction of CO2 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 CO2 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 CO2 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 CO2 sequestration capacities between 344.8 and 432.3 g CO2 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 CO2 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.
Keywords: enforced carbonation, maximum sequestration capacity, leaching, heavy metals, mineralogy, bio-based ash
Published in DiRROS: 13.01.2026; Views: 521; Downloads: 471
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Abstract: Artificial aggregates offer a sustainable solution to large-scale waste utilization and the increasing demand for limited natural aggregates. This study extends the understanding of the production of artificial lightweight aggregates with a variable rotation speed approach based solely on biomass fly ash (BFA) alkali-activated materials (AAMs). Systematic variation of alkali content and solution density at a constant water-to-solids ratio showed that alkali concentration significantly influences granulation beyond what can be explained by water availability. The interplay between alkali activation and carbonation was investigated using different mix designs and curing conditions, as well as comparing simultaneous curing carbonation with post-cure carbonation. The results were evaluated with regard to the effects on the macro- and microstructural properties as well as on the leaching behavior. Prolonged carbonation initiated after aggregate formation resulted in premature depletion of Ca, limiting the development of C-A-S-H gels and increasing microporosity, leading to a reduction in mechanical properties. In contrast, post-curing carbonation maintained a compressive strength of over 1 MPa while still allowing carbonation benefits, resulting in compressive strengths comparable to lightweight expanded clay aggregates. Carbonation also proved to be an effective leaching mitigation strategy by stabilizing heavy metals through both physical encapsulation and chemical pH regulation. These results underline the importance of carbonation timing in high Ca AAMs and highlight lightweight aggregates as a viable pathway for BFA valorization, CO₂ sequestration and sustainable construction applications. This approach offers an alternative valorization strategy for BFA facing regulatory restrictions for direct use in cement, while contributing to carbon capture and circular economy initiatives.
Keywords: artificial aggregates, lightweight aggregates, biomass ash, alkali-activated materials, leaching, carbonation
Published in DiRROS: 18.07.2025; Views: 1193; Downloads: 1204
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Abstract: This review provides an overview of methods to extract valuable resources from the ash fractions of sewage sludge, municipal solid waste, and wood biomass combustion. The resources addressed here include critical raw materials, such as phosphorus, base and precious metals, and rare earth elements for which it is increasingly important to tap into secondary sources in addition to the mining of primary raw materials. The extraction technologies prioritized in this review are based on recycled acids or excess renewable energy to achieve an optimum environmental profile for the extracted resources and provide benefits in the form of local industrial symbioses. The extraction methods cover all scarce and valuable chemical elements contained in the ashes above certain concentration limits. Another important part of this review is defining potential applications for the mineral residues remaining after extraction. Therefore, the aim of this review is to combine the knowledge of resource extraction technology from ashes with possible applications of mineral residues in construction and related sectors to fully close material cycle loops.
Keywords: critical raw materials, extraction, sewage sludge ash, municipal solid waste incineration ash, wood biomass ash
Published in DiRROS: 03.11.2023; Views: 2297; Downloads: 1394
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