This contribution reviews the geopolymeric potential of Ca-rich oil shale processing residues and aims at the characterization of the effects of different alkaline activator solutions on the polymerization of oil shale processing residues experimentally tested in recent-case studies. The analysis shows that the alkali activation of Estonian oil shale solid wastes is controlled by the presence and dissolution of reactive Ca-bearing phases. However, the geopolymeric potential of oil shale ashes is limited by the amount of available reactive Si and Al in the source material. Excess Ca in activated samples is precipitated as Ca-hydroxide showing Si deficiency in the system. To induce a substantial polymer formation, additional sources of readily available Si and Al must be introduced in the mix design. In addition, for industrial applications, further optimization of the mix design and curing conditions, including thermal curing, is needed to reduce dry shrinkage and microstructural cracking.
1. Davidovits, J. Geopolymer Chemistry and Applications. 4th Edition. Institut Géopolymère, Saint-Quentin, 2011.
2. Duxson, P., Fernandez-Jimenez, A., Provis, J. L., Lukey, G. C., Palomo, A., van Deventer, J. S. J. Geopolymer technology: the current state of the art. J. Mater. Sci., 2007, 42(9), 2917‒2933.
https://doi.org/10.1007/s10853-006-0637-z
3. Li, Q., Xu, H., Li, F. H., Li, P. M., Shen, L. F., Zhai, J. P. Synthesis of geopolymer composites from blends of CFBC fly and bottom ashes. Fuel, 2012, 97, 366‒372.
https://doi.org/10.1016/j.fuel.2012.02.059
4. Van Riessen, A. Thermo-mechanical and microstructural characterisation of sodium-poly(sialate-siloxo) (Na-PSS) geopolymers. J. Mater. Sci., 2007, 42(9), 3117‒3123.
https://doi.org/10.1007/s10853-006-0522-9
5. Zhang, Z. H., Wang, H., Zhu, Y. C., Reid, A., Provis, J. L., Bullen, F. Using fly ash to partially substitute metakaolin in geopolymer synthesis. Appl. Clay Sci., 2014, 88‒89, 194‒201.
https://doi.org/10.1016/j.clay.2013.12.025
6. Guo, X. L., Shi, H. S., Chen, L. M., Dick, W. A. Alkali-activated complex binders from class C fly ash and Ca-containing admixtures. J. Hazar. Mater., 2010, 173(1‒3), 480‒486.
https://doi.org/10.1016/j.jhazmat.2009.08.110
7. Guo, X. L., Shi, H. S., Dick, W. A. Compressive strength and microstructural characteristics of class C fly ash geopolymer. Cement Concrete Comp., 2010, 32(2), 142‒147.
https://doi.org/10.1016/j.cemconcomp.2009.11.003
8. Mijarsh, M. J. A., Johari, M. A. M., Ahmad, Z. A. Effect of delay time and Na2SiO3 concentrations on compressive strength development of geopolymer mortar synthesized from TPOFA. Constr. Build. Mater., 2015, 86, 64‒74.
https://doi.org/10.1016/j.conbuildmat.2015.03.078
9. Bernal, S. A., Rodriguez, E. D., Kirchheim, A. P., Provis, J. L. Management and valorisation of wastes through use in producing alkali-activated cement materials. J. Chem. Technol. Biot., 2016, 91(9), 2365‒2388.
https://doi.org/10.1002/jctb.4927
10. Provis, J. L., Palomo, A., Shi, C. J. Advances in understanding alkali-activated materials. Cement Concrete Res., 2015, 78, Part A, 110‒125.
https://doi.org/10.1016/j.cemconres.2015.04.013
11. Bauert, H., Kattai, V. Kukersite oil shale. In: Geology and Mineral Resources of Estonia (Raukas, A., Teedumäe, A., eds.). Estonian Academy Publishers, Tallinn, 1997, 313‒327.
12. Ots, A. Oil Shale Fuel Combustion. Tallinna Raamatutrükikoda, Tallinn, 2006, 833.
13. Pets, L. I., Vaganov, P. A.., Knoth, J., Haldna, Ü L., Schwenke, H., Schnier, C., Juga, R. J. Microelements in oil-shale ash of the Baltic Thermoelectric Power Plant. Oil Shale, 1985, 2(4), 379–390 (in Russian, summary in English).
14. Hanni, R. Energy and valuable material by-product from firing Estonian oil shale. Waste Manage., 1996, 16(1‒3), 97‒99.
https://doi.org/10.1016/S0956-053X(96)00054-2
15. Kaasik, A., Vohla, C., Mõtlep, R., Mander, U., 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.
https://doi.org/10.1016/j.watres.2007.10.002
16. Kasak, K., Mõtlep, R., Truu, M., Truu, J., Kõiv-Vainik, M., Espenberg, M., Paiste, P., Kirsimäe, K., Mander, Ü. Hydrated oil shale ash mitigates greenhouse gas emissions from horizontal subsurface flow filters for wastewater treatment. Water Air Soil Poll., 2016, 227(9), 1‒12.
https://doi.org/10.1007/s11270-016-3007-8
17. 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.
https://doi.org/10.1016/j.watres.2010.06.044
18. Kõiv, M., Ostonen, I., Vohla, C., Mõtlep, R., Liira, M., Lõhmus, K., Kirsimäe, K., Mander, Ü. Reuse potential of phosphorus-rich filter materials from subsurface flow wastewater treatment filters for forest soil amendment. Hydrobiologia, 2012, 692(1), 145‒156.
https://doi.org/10.1007/s10750-011-0944-5
19. Liira, M., Kõiv, M., Mander, Ü., Mõtlep, R., Vohla, C., Kirsimäe, K. Active filtration of phosphorus on Ca-rich hydrated oil shale ash: does longer retention time improve the process? Environ. Sci. Technol., 2009, 43(10), 3809‒3814.
https://doi.org/10.1021/es803642m
20. 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.
https://doi.org/10.3176/oil.2010.4.07
21. Mõtlep, R., Kirsimäe, K., Talviste, P., Puura, E., Jürgenson, J. Mineral composition of Estonian oil shale semi-coke sediments. Oil Shale, 2007, 24(3), 405‒422.
22. Siirde, A., Roos, I., Martins, A. Estimation of carbon emission factors for the Estonian shale oil industry. Oil Shale, 2011, 28(1S), 127‒139.
https://doi.org/10.3176/oil.2011.1S.05
23. 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.
https://doi.org/10.3176/oil.2016.4.05
24. Paaver, P., Paiste, P., Mõtlep, R., Kirsimäe, K. Self-cementing properties and alkali activation of Enefit280 solid heat carrier retorting ash. Oil Shale, 2017, 34(3), 263‒278.
https://doi.org/10.3176/oil.2017.3.05
25. 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.
https://doi.org/10.1016/j.conbuildmat.2016.06.073
26. Paiste, P., Külaviir, M., Paaver, P., Heinmaa, I., Vahur, S., Kirsimäe, K. Beneficiation of oil shale processing waste: secondary binder phases in alkali activated composites. Waste Biomass Valori., 2017, 1‒11.
https://doi.org/10.1007/s12649-017-0140-6
27. World Energy Council. World Energy Resources: 2013 Survey. World Energy Council, London, 2013. Available at https://www.worldenergy.org/wp-content/uploads/2013/09/Complete_WER_2013_Survey.pdf
28. Liira, M., Kirsimäe, K., Kuusik, R., Mõtlep, R. Transformation of calcareous oil-shale circulating fluidized-bed combustion boiler ashes under wet conditions. Fuel, 2009, 88(4), 712‒718.
https://doi.org/10.1016/j.fuel.2008.08.012
29. 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(1), 172‒180.
https://doi.org/10.1016/j.fuel.2011.08.050
30. Siirde, A., Eldermann, M., Rohumaa, P., Gusca, J. Analysis of greenhouse gas emissions from Estonian oil shale based energy production processes. Life cycle energy analysis perspective. Oil Shale, 2013, 30(2S), 268‒282.
https://doi.org/10.3176/oil.2013.2S.07
31. Aarna, I. Developments in production of synthetic fuels out of Estonian oil shale. Energ. Environ., 2011, 22(5), 541‒552.
https://doi.org/10.1260/0958-305X.22.5.541
32. Soone, J., Doilov, S. Sustainable utilization of oil shale resources and comparison of contemporary technologies used for oil shale processing. Oil Shale, 2003, 20(3S), 311‒323.
33. Golubev, N. Solid oil shale heat carrier technology for oil shale retorting. Oil Shale, 2003, 20(3S), 324‒332.
34. Talviste, P., Sedman, A., Mõtlep, R., Kirsimäe, K. Self-cementing properties of oil shale solid heat carrier retorting residue. Waste Manage. Res., 2013, 31(6), 641‒647.
https://doi.org/10.1177/0734242X13482033
35. Sedman, A., Talviste, P., Kirsimäe, K. The study of hydration and carbonation reactions and corresponding changes in the physical properties of co-deposited oil shale ash and semicoke wastes in a small-scale field experiment. Oil Shale, 2012, 29(3), 279‒294.
https://doi.org/10.3176/oil.2012.3.07
36. 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.
https://doi.org/10.3176/oil.2012.4.08
37. Faucon, P., Delagrave, A., Richet, C., Marchand, J. M., Zanni, H. Aluminum incorporation in calcium silicate hydrates (C‒S‒H) depending on their Ca/Si ratio. J. Phys. Chem. B, 1999, 103(37), 7796‒7802.
https://doi.org/10.1021/jp990609q
38. Sun, G. K., Young, J. F., Kirkpatrick, R. J. The role of Al in C‒S‒H: NMR, XRD, and compositional results for precipitated samples. Cement Concrete Res., 2006, 36(1), 18‒29.
https://doi.org/10.1016/j.cemconres.2005.03.002
39. Yip, C. K., Lukey, G. C., van Deventer, J. S. J. The coexistence of geopolymeric gel and calcium silicate hydrate at the early stage of alkaline activation. Cement Concrete Res., 2005, 35(9), 1688‒1697.
https://doi.org/10.1016/j.cemconres.2004.10.042
40. Komnitsas, K. A. Potential of geopolymer technology towards green buildings and sustainable cities. The GBSC 2011 paper. Procedia Engineering, 2011, 21, 1023‒1032.
https://doi.org/10.1016/j.proeng.2011.11.2108
41. Xu, H., van Deventer, J. S. J. The geopolymerisation of alumino-silicate minerals. Int. J. Miner. Process., 2000, 59(3), 247‒266.
https://doi.org/10.1016/S0301-7516(99)00074-5
42. Van Deventer, J. S. J., Provis, J. L., Duxson, P., Lukey, G. C. Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products. J. Hazard. Mater., 2007, 139(3), 506‒513.
https://doi.org/10.1016/j.jhazmat.2006.02.044
43. Castel, A., Foster, S. J., Ng, T., Sanjayan, J. G., Gilbert, R. I. Creep and drying shrinkage of a blended slag and low calcium fly ash geopolymer Concrete. Mater. Struct., 2016, 49(5), 1619‒1628.
https://doi.org/10.1617/s11527-015-0599-1
44. Duxson, P., Provis, J. L. Designing precursors for geopolymer cements. J. Am. Ceram. Soc., 2008, 91(12), 3864‒3869.
https://doi.org/10.1111/j.1551-2916.2008.02787.x
45. Buchwald, A., Dombrowski, K., Weil, M. The influence of calcium content on the perfomance of geopolymeric binder especially the resistance against acids. In: Geopolymer, Green Chemistry and Sustainable Development Solutions (Davidovits, J., ed.). Institut Géopolymère, St. Quentin, France, 2005, 35‒39.
46. Aughenbaugh, K. L., Williamson, T., Juenger, M. C. G. Critical evaluation of strength prediction methods for alkali-activated fly ash. Mater. Struct., 2015, 48(3), 607‒620.
https://doi.org/10.1617/s11527-014-0496-z
