title: Composition, diagenetic transformation and alkalinity potential of oil shale ash sediments.
abstract: Oil shale is a primary fuel in the Estonian energy sector. After combustion 45-48% of the oil shale is left over as ash, producing about 5-7 Mt of ash, which is deposited on ash plateaus annually almost without any reuse. This study focuses on oil shale ash plateau sediment mineralogy, its hydration and diagenetic transformations, a study that has not been addressed. Oil shale ash wastes are considered as the biggest pollution sources in Estonia and thus determining the composition and properties of oil shale ash sediment are important to assess its environmental implications and also its possible reusability. A study of fresh ash and drillcore samples from ash plateau sediment was conducted by X-ray diffractometry and scanning electron microscopy. The oil shale is highly calcareous, and the ash that remains after combustion is derived from the decomposition of carbonate minerals. It is rich in lime and anhydrite that are unstable phases under hydrous conditions. These processes and the diagenetic alteration of other phases determine the composition of the plateau sediment. Dominant phases in the ash are hydration and associated transformation products: calcite, ettringite, portlandite and hydrocalumite. The prevailing mineral phases (portlandite, ettringite) cause highly alkaline leachates, pH 12-13. Neutralization of these leachates under natural conditions, by rainwater leaching/neutralization and slow transformation (e.g. carbonation) of the aforementioned unstable phases into more stable forms, takes, at best, hundreds or even hundreds of thousands of years.
authors.affiliation: Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia. Electronic address: riho.motlep@ut.ee.
authors.forename: Riho
authors.initials: R
authors.lastname: Mõtlep
authors.affiliation: Estonian Land Board, Mustamäe tee 51, 10621 Tallinn, Estonia. Electronic address: terje.sild@maaamet.ee.
authors.forename: Terje
authors.initials: T
authors.lastname: Sild
authors.affiliation: Institute of Technology, University of Tartu, Nooruse 1, 50411 Tartu, Estonia. Electronic address: erik.puura@ut.ee.
authors.forename: Erik
authors.initials: E
authors.lastname: Puura
authors.affiliation: Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia. Electronic address: kalle.kirsimae@ut.ee.
authors.forename: Kalle
authors.initials: K
authors.lastname: Kirsimäe
mesh_terms: D000468:Alkalies / Q000737:chemistry*; D019015:Geologic Sediments; D008855:Microscopy, Electron, Scanning; D010578:Petroleum; D014961:X-Ray Diffraction
chemical_list: D000468:Alkalies; D010578:Petroleum