Mineral carbonation of thermally treated and weathered biomass ashes with respect to their CO2 capture and storage

Abstract

Five long-term stored biomass ashes (BAs) from beech wood chips, corn cobs, sunflower shells, plum pits, and walnut shells produced at 500 °C were thermally treated at 900 °C and subsequently weathered to evaluate their CO2 capture and storage (CCS) potential by mineral carbonation. A combination of different mineralogical, chemical and thermal analyses was used for that purpose. The BAs studied are highly enriched in alkaline-earth and alkaline oxides (52–91%) and they belong to diverse chemical ash types. The minerals responsible for CCS of these BAs include Ca, K, K-Ca and Ca-Mg carbonates and bicarbonates such as calcite, fairchildite, kalicinite, dolomite, and butschliite. The formation of these minerals is a result of interactions between alkaline-earth and alkaline oxyhydroxides in BA and flue CO2 gas during residual char combustion and especially atmospheric CO2 during BA storage and weathering. It was found that the BAs studied show significant CCS capacity, namely about 19–33% (mean 27%). It was emphasized that the renewable and carbon-neutral biomass also has some extra CCS potential due to the sequestration of atmospheric CO2 during BA storage and weathering. Therefore, the future large-scale bioenergy production in a sustainable way can contribute greatly for decreasing CO2 emissions in the atmosphere and can reduce the use of costly CCS technologies.