Power generation and other industries using solid fossil fuels like coal, lignite, oil shale and peat are responsible for producing large quantities of solid residues that are often chemically reactive and/or unstable and are disposed in holding ponds and deposition sites. Stability and long-term behaviour of such deposits are typically studied in short-term laboratory experiments that cannot describe nor predict long-term changes taking place in these materials. Here, we study long-term (>40 years) transformations, in highly alkaline conditions, of the Ca-rich ash deposit in Estonia composed of oil shale processing residues from the Eesti power plant. Detailed mineralogical,

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 CO 2 sequestration. The authors studied the long-term CO 2 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 CO 2 in Europe. The study shows that ash deposits are currently only partially carbonated, with an average CO 2 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 CO 2 binding potential could rise to ca 200 kg per tonne of ash.

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