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In order to reach future goals of net carbon neutrality and climate change mitigation, various carbon capture and sequestration techniques must be implemented. Industrial waste rich in chemically active alkaline metal oxides is considered as a potential material for CO2 sequestration. The authors studied the long-term CO2 binding capacity of Ca-rich oil shale ash (OSA) deposits at oil shale(OS)-fired power plants of Estonia and estimated the remaining sequestration potential for in-situ carbonation. Providing energy security, the Estonian oil shale industry is the biggest national producer of solid waste and the leading greenhouse gas emitter, making the country one of the largest per capita producers of CO2 in Europe. The study shows that ash deposits are currently only partially carbonated, with an average CO2 binding rate of 51 kg per tonne of hydrated sediment, most of which being bound in such carbonate minerals as calcite and vaterite, as well as in Ca-silicate thaumasite. It is estimated that at full carbonation of reactive Ca and Mg phases in ash (portlandite, ettringite and semicrystalline C-S-H), the projected average total CO2 binding potential could rise to ca 200 kg per tonne of ash. [ABSTRACT FROM AUTHOR]

Abstract Groundwater in the Cambrian-Vendian aquifer system in Estonia is characterised by the most depleted isotopic composition known in Europe (δ18O down to −23‰). The water most likely originates from glacial meltwater recharge from the Fennoscandian Ice Sheet in the Pleistocene. The aquifer system is characterised by relative high methane concentrations (up to 50% of dissolved gases, estimated absolute concentration up to 1600 μmol L−1), the origin of which has so far remained unclear. In this paper, we focus on the origin of methane, the factors controlling its spatial distribution and its isotope geochemistry in the aquifer system. The data reveal a large spatial variability in methane concentration, δ13C CH4 and δ2H CH4 values (from −6 to −105‰ and from −220 to −420‰, respectively). We show that local oxidation processes rather than different pathways of methane formation, have affected the initial isotopic composition of methane. Using the least modified δ13C CH4 values (from −85 to −105‰), we conclude that methane most likely originates from the organic material overridden by the Fennoscandian Ice Shield during the Late Weichselian glaciation, that was carried into the aquifer system with infiltrating glacial meltwater. The estimated δ18O values of the water, where the methane was formed, are −17 ± 1.5‰ supporting the inference that the methane was formed during the Middle Weichselian interstadial. The study shows that groundwater of glacial origin in the Cambrian-Vendian aquifer system can serve as an alternative palaeoenvironmental archive to be used for studying the variations in climatic and environmental conditions in Northern Europe during glacial–interglacial cycles of the Pleistocene. [ABSTRACT FROM AUTHOR]