eesti teaduste
akadeemia kirjastus
SINCE 1984
Oil Shale cover
Oil Shale
ISSN 1736-7492 (Electronic)
ISSN 0208-189X (Print)
Impact Factor (2020): 0.934

The composition and properties of ash in the context of the modernisation of oil shale industry; pp. 155–176

Full article in PDF format | 10.3176/oil.2021.2.04

Mai Uibu, Kadriann Tamm, Regiina Viires, Janek Reinik, Peeter Somelar, Lembi-Merike Raado, Tiina Hain, Rein Kuusik, Andres Trikkel


The modernisation of the oil shale (OS) industry in Estonia over the last decade has also led to significant changes in the composition and binding properties of the ash generated as a by-product. These changes also influence the environmental impact that the ash can have. In the current investigation, oil shale ash (OSA) samples were collected from different points along the ash separation systems of a large pulverized fuel combustion plant (LCP), various points in a circulating fluidized bed (CFB) combustion plant, and from an oil shale pyrolysis plant that utilises oil shale to produce liquid fuels. The results obtained can be used for optimising the deposition conditions, as well as guiding utilisation-recycling processes for ash generated from changing oil shale composition and characteristics. When it comes to developing the circular economy aspects of oil shale utilisation, mapping out the properties of OSA is crucial. 


1. Ots, A. Oil Shale Fuel Combustion. Tallinn University of Technology, Tallinn, 2006.

2. Neshumayev, D., Pihu, T., Siirde, A., Järvik, O., Konist, A. Solid heat carrier oil shale retorting technology with integrated CFB technology. Oil Shale, 2019, 36(2S), 99‒113.

3. Konist, A., Pikkor, H., Neshumayev, D., Loo, L., Järvik, O., Siirde, A., Pihu, T. Co-combustion of coal and oil shale blends in circulating fluidized bed boilers. Oil Shale, 2019, 36(2), 114‒127.

4. Hotta, A., Parkkonen, R., Hiltunen, M., Arro, H., Loosaar, J., Parve, T., Pihu, T., Prikk, A., Tiikma, T. Experience of Estonian oil shale combustion based on CFB technology at Narva Power Plants. Oil Shale, 2006, 22(4S), 381‒397.

5. Pihu, T., Arro, H., Prikk, A., Parve, T., Loosaar, J. Combustion Experience of Estonian Oil Shale in Large Power Plants. In: International Conference on Oil Shale: “Recent Trends in Oil Shale”, 7‒9 November 2006, Amman, Jordan, 2006.

6. Pihu, T., Konist, A., Neshumayev, D., Loo, L., Molodtsov, A., Valtsev, A. Full-scale tests on the co-firing of peat and oil shale in an oil shale fired circulating fluidized bed boiler. Oil Shale, 2017, 34(3), 250‒262.

7. Konist, A., Valtsev, A., Loo, L., Pihu, T., Liira, M., Kirsimäe, K. Influence of oxy-fuel combustion of Ca-rich oil shale fuel on carbonate stability and ash composition. Fuel, 2015, 139, 671‒677.

8. Loo, L., Maaten, B., Siirde, A., Pihu, T., Konist, A. Experimental analysis of the combustion characteristics of Estonian oil shale in air and oxy-fuel atmospheres. Fuel Process Technol, 2015, 134, 317‒324.

9. Yörük, C. R., Meriste, T., Sener, S., Kuusik, R., Trikkel, A. Thermogravimetric analysis and process simulation of oxy-fuel combustion of blended fuels including oil shale, semicoke, and biomass. Int. J. Energ. Res., 2018, 42(6), 2213‒2224.

10. Yörük, C. R, Trikkel, A., Kuusik, R. Prediction of flue gas composition and comparative overall process evaluation for air and oxyfuel combustion of Estonian oil shale, using Aspen Plus Process Simulation. Energy Fuels, 2016, 30(7), 5893‒5900.

11. Kuusik, R., Uibu, M., Kirsimäe, K., Mõtlep, R., Meriste, T. Open-air deposition of Estonian oil shale ash: Formation, state of art, problems and prospects for the abatement of environmental impact. Oil Shale, 2012, 29(4), 376‒403.

12. Pihu, T., Arro, H., Prikk, A., Rootamm, R., Konist, A., Kirsimäe, K., Liira, M., Mõtlep, R. Oil shale CFBC ash cementation properties in ash fields. Fuel, 2012, 93, 172‒180.

13. Bityukova, L., Mõtlep, R., Kirsimäe, K. Composition of oil shale ashes from pulverized firing and circulating fluidized-bed boiler in Narva Thermal Power Plants, Estonia. Oil Shale, 2010, 27(4), 339‒353.

14. Mõtlep, R., Sild, T., Puura, E., Kirsimäe, K. Composition, diagenetic transformation and alkalinity potential of oil shale ash sediments. J. Hazard. Mater., 2010, 184(1‒3), 567–573.

15. Raado, L.-M., Kuusik, R., Hain, T., Uibu, M., Somelar, P. Oil shale ash based stone formation ‒ hydration, hardening dynamics and phase transformations. Oil Shale, 2014, 31(1), 91‒101.

16. Irha, N., Uibu, M., Jefimova, J., Raado, L.-M., Hain, T., Kuusik, R. Leaching behaviour of Estonian oil shale ash-based construction mortars. Oil Shale, 2014, 31(4), 394‒411.

17. Paaver, P., Paiste, P., Liira, M., Kirsimäe, K. Alkali activation of Estonian Ca-rich oil shale ashes: a synthesis. Oil Shale, 2019, 36(2S), 214‒225.

18. Usta, M. C., Yörük, C. R., Hain, T., Paaver, P., Snellings, R., Rozov, E., Gregor, A., Kuusik, R., Trikkel, A., Uibu, M. Evaluation of new applications of oil shale ashes in building materials. Minerals, 2020, 10(9), 765.

19. Liiv, J., Teppand, T., Rikmann, E., Tenno, T. Novel ecosustainable peat and oil shale ash-based 3D-printable composite material. SM&T, 2018, 17, e00067.

20. Paiste, P., Liira, M., Heinmaa, I., Vahur, S., Kirsimäe, K. Alkali activated construction materials: Assessing the alternative use for oil shale processing solid wastes. Constr. Build. Mater., 2016, 122, 458‒464.

21. Berber, H., Tamm, K., Leinus, M.-L., Kuusik, R., Uibu, M. Aggregate production from burnt oil shale and CO2 – an Estonian perspective. Oil Shale, 2019, 36(3), 431‒447.

22. Berber, H., Tamm, K., Leinus, M.-L., Kuusik, R., Tõnsuaadu, K., Paaver, P., Uibu, M. Accelerated carbonation technology granulation of industrial waste: Effects of mixture composition on product properties. Waste Manage. Res., 2020, 38(2), 142‒155.

23. Talviste, P., Kirsimäe, K. Reuse of oil shale fly ash as a hydraulic binder for strengthening soft soils. IPT Projektijuhtimine, Töö Nr 16-11-1304 (in Estonian). (accessed 23.09.2020).

24. Uibu, M., Somelar, P., Raado, L.-M., Irha, N., Hain, T., Koroljova, A., Kuusik, R. Oil shale ash based backfilling concrete ‒ Strength development, mineral transformations and leachability. Constr. Build. Mater., 2016, 102(Part 1), 620‒630.

25. Loide, V. Relieving the calcium deficiency of field soils by means of liming. Agron. Res., 2010, 8(IIS), 415‒420.

26. Kaljuvee, T., Jefimova, J., Loide, V., Uibu, M., Einard, M. Influence of the post-granulation treatment on the thermal behaviour and leachability characteristics of Estonian oil shale ashes. J. Therm. Anal. Calorim., 2018, 132(1), 47‒57.

27. Velts, O., Uibu, M., Kallas, J., Kuusik, R. Waste oil shale ash as a novel source of calcium for precipitated calcium carbonate: Carbonation mechanism, modeling, and product characterization. J. Hazard. Mater., 2011, 195, 139‒146.

28. Uibu, M., Velts, O., Kuusik, R. Developments in CO2 mineral carbonation of oil shale ash. J. Hazard. Mater., 2010, 174(1‒3), 209‒214.

29. Uibu, M., Tamm, K., Velts-Jänes, O., Kallaste, P., Kuusik, R., Kallas, J. Utilization of oil shale combustion wastes for PCC production: Quantifying the kinetics of Ca(OH)2 and CaSO4·2H2O dissolution in aqueous systems. Fuel Process. Technol., 2015, 140, 156‒164.

30. Paaver, P., Paiste, P., Kirsimäe, K. Geopolymeric potential of the Estonian oil shale solid residues: Petroter solid heat carrier retorting ash. Oil Shale, 2016, 33(4), 373‒392.

31. Reinik, J., Heinmaa, I., Mikkola, J.-P., Kirso, U. Hydrothermal alkaline treatment of oil shale ash for synthesis of tobermorites. Fuel, 2007, 86(5‒6), 669‒676.

32. Reinik, J., Heinmaa, I., Kirso, U., Kallaste, T., Ritamäki, J., Boström, D., Pongrácz, E., Huuhtanen, M., Larsson, W., Keiski, R., Kordás, K., Mikkola, J.-P. Alkaline modified oil shale fly ash: Optimal synthesis conditions and preliminary tests on CO2 adsorption. J. Hazard. Mater., 2011, 196, 180‒186.

33. Reinik, J., Heinmaa, I., Mikkola, J.-P., Kirso, U. Synthesis and characterization of calcium‒alumino-silicate hydrates from oil shale ash ‒ Towards industrial applications. Fuel, 2008, 87(10‒11), 1998‒2003.

34. Kaasik, A., Vohla, C., Mõtlep, R., Mander, Ü., Kirsimäe, K. Hydrated calcareous oil-shale ash as potential filter media for phosphorus removal in constructed wetlands. Water Res., 2008, 42(4‒5), 1315‒1323.

35. Kõiv, M., Liira, M., Mander, U., Mõtlep, R., Vohla, C., Kirsimäe, K. Phosphorus removal using Ca-rich hydrated oil shale ash as filter material ‒ the effect of different phosphorus loadings and wastewater compositions. Water Res., 2010, 44(18), 5232‒5239.

36. Kuusik, R., Uibu, M., Toom, M., Muulmann, M.-L., Kaljuvee, T., Trikkel, A. Sulphation and carbonization of oil shale CFBC ashes in heterogeneous systems. Oil Shale, 2005, 22(4S), 421‒434.

37. Yörük, C. R., Uibu, M., Usta, M. C., Kaljuvee, T., Trikkel, A. CO2 mineralization by burnt oil shale and cement bypass dust: effect of operating temperature and pre-treatment. J. Therm. Anal. Calorim., 2020, 142, 991‒999.

38. Reispere, H. J. Determination of free CaO content in oil shale ash. Trans. Tallinn Polytech. Institute, Ser A Nr 245, 1966, 73‒76 (in Estonian).

39. EVS 664:1995. Solid Fuels. Sulphur Content. Determination of Total Sulphur and its Bonding Forms. 1995 (in Estonian).

40. UNI EN 12457-2: 2004. Leaching – Compliance Test for Leaching of Granular Waste Materials and Sludges. Part 2: One Stage Batch Test at a Liquid to Solid Ratio of 10 l/kg for Materials with Particle Size below 4 mm.

41. DIN EN 16171:2016. Sludge, Treated Biowaste and Soil ‒ Determination of Elements Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

42. DIN EN ISO 10523:2012. Water Quality ‒ Determination of pH.

43. DIN EN 27888 (C8). Water Quality ‒ Determination of Electrical Conductivity.

44. DIN EN ISO 17294-2 (E29). Water Quality ‒ Application of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) ‒ Part 2: Determination of Selected Elements Including Uranium Isotopes.

45. DIN EN ISO 10304-1 (D20). Determination of Dissolved Anions by Liquid Chromatography of Ions ‒ Part 1: Determination of Bromide, Chloride, Fluoride, Nitrate, Nitrite, Phosphate and Sulfate.

46. EVS-EN 196-6:2018. Methods of Testing Cement ‒ Part 6: Determination of Fineness.

47. EVS-EN 933-1:2012. Tests for Geometrical Properties of Aggregates. Part 1: Determination of Particle Size Distribution. Sieving Method.

48. EVS-EN 196-5:2011. Methods of Testing Cement ‒ Part 5: Pozzolanicity Test for Pozzolanic Cement.

49. EVS-EN 196-3:2016. Methods of Testing Cement ‒ Part 3: Determination of Setting Times and Soundness.

50. EVS-EN 196-1:2016. Methods of Testing Cement ‒ Part 1: Determination of Strength.

51. Kuusik, R., Uibu, M., Kirsimäe, K. Characterization of oil shale ashes formed at industrial-scale CFBC boilers. Oil Shale, 2005, 22(4S), 407‒419.

52. Saether, O. M., Banks, D., Kirso, U., Bityukova, L., Sorlie, J.-E. The chemistry and mineralogy of waste from retorting and combustion of oil shale. In: Energy, Waste and the Environment: a Geochemical Perspective (Gieré, R., Stille, P., Eds.)Geol. Soc., London. Special Publications, 236, 2004, 263.

53. Laja, M., Urb, G., Irha, N., Reinik, J., Kirso, U. Leaching behavior of ash fractions from oil shale combustion by fluidized bed and pulverized firing process. Oil Shale, 2005, 22(3), 453‒465.

54. Reinik, J., Irha, N., Steinnes, E., Piirisalu, E., Aruoja, V., Schultz, E., Leppänen, M. Characterization of water extracts of oil shale retorting residues from gaseous and solid heat carrier processes. Fuel Process. Technol., 2015, 131, 443‒451.

55. Tamm, K., Kallaste, P., Uibu, M., Kallas, J., Velts-Jänes, O., Kuusik, R. Leaching thermodynamics and kinetics of oil shale waste key components. Oil Shale, 2016, 33(1), 80‒99.

56. Potential Hazardousness of Estonian Oil Shale Ashes. Report, 1.07.2019, Tallinn University of Technology and University of Tartu (in Estonian). (accessed 8.11.2019).

57. Eesti Energia. Oil Shale Ash, 2018. (accessed 21.03.2019).

58. Directive 2013/39/EU of the European Parliament and of the Council of 12 August 2013 Amending Directives 2000/60/EC and 2008/105/EC as Regards Priority Substances in the Field of Water Policy. Official Journal of the European Union, L 226, 24.8.2013.

59. The Environmental Quality Limit Values for the Surface Water and Their Methods of Application, and the Environmental Quality Limit Values for Water Biota. Riigi Teataja I, 18.12.2013, 5 (in Estonian).

60. Irha, N., Reinik, J., Steinnes, E., Urb, G., Kirso, U., Jefimova, J. Leachability of trace elements from the aged and fresh spent shale deposit – A field study. Oil Shale, 2013, 30(3), 456‒467.

61. EVS 636:2002. Burnt Oil-Shale for Production Portland Burnt Shale Cement, Portland Composite Cement and Masonry Cement. Withdrawn on 03.12.2015.

62. Kikas, W. Composition and binder properties of Estonian kukersite oil shale ash. ZKG Int., 1997, 50(2), 112‒126.

63. EVS 927: 2018. Burnt Shale for Building Materials: Specification, Performance and Conformity.

64. Ragn-Sells filed patent applications for the enhancement of oil shale ash, ERR News 26.06.2020.

65. Kuusik, R., Uus, M., Uibu, M., Stroganov, G., Parts, O., Trikkel, A., Pepoyan, V., Terentiev, A., Kalnapenk, E. Method for Neutralization of Alkaline Waste Water with Carbon Dioxide Consisting in Flue Gas. Patent EE200600041, priority date 22.12.2006.

66. Kuusik, R., Uibu, M., Uus, M., Velts-Jänes, O., Trikkel, A., Veinjärv, R. Method for Eliminating CO2 from Flue Gases by Calcium Compounds Containing Industrial Wastes. Patent P200900040, priority date 8.06.2009.

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