Zeolitized bottom ashes from biomass combustion as cement replacing components

In power plants biomass combustion produces large quantities of biomass bottom ash wastes. During the combustion process, the produced ashes are enriched in the radionuclides. The different enrichment of the various radionuclides within a radioactive series, such as that of 226Ra, 228Ra, 228Th, 40K, 210Pb and 137Cs results in the disturbance of radioactive secular equilibrium. The production of energy from renewable resources, such as biomass, is increasing rapidly. As the demand for bioenergy production increases, waste products from biomass combustion will increase too and will become a relevant environmental and economic problem. Therefore, environmentally friendly, and economic solutions to recycle the resulting by-products are essential. This research provides a real opportunity to save cement thus disposing the waste by using zeolitized biomass bottom ash as supplementary cementitious materials. The zeolitized products were examined by X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF) spectroscopy and high-resolution gamma spectrometry. In all investigated cases, compressive strength in hardened cement pastes and concrete samples slightly increases by replacing from 3% to 5% of Portland cement with zeolitized ashes. The results showed that natural radionuclides as 226Ra, 228Ra, 228Th, 40K are concentrated in similar way as in case of ashes obtained from combustion. However, addition of biomass leads to concentration of artificial radionuclide 137Cs that is still commonly present in biomass due to Chernobyl disaster. The observed activity concentration of 137Cs reaches the level of natural radionuclides concentration. Taking into consideration the contribution of 137Cs to gamma dose (usage of expanded activity index formula) may lead to exceeding the value of 1 in some cases. Calculated differences between activity indexes reach 13%.