Adsorbents from Lignite Fly Ash Capturing Heavy Metals and Co2

Intergovernmental Panel on Climate Change (IPCC) declared the alleviation of greenhouse gases (GHGs) emissions as a target for slowing down the climate change. The goal necessitates extensive deployment of carbon mitigation technologies, including carbon capture, permanent long-term utilisation or storage technologies (CC-U-S). Such deployment of CC-U-S must address economy sectors requiring direct decarbonisation, i.e., heavy industries, cement production, and heat and power generation sites using renewable fuels, e.g., biomass and municipal solid wastes.
Post-combustion application of CC-U-S is one of the most feasible approaches with large-scale operation experience. Absorption with liquids and adsorption with solid sorbents possess a potential of use at fossil fuel power and heat plants, being combined with the flue-gas purification. The transfer of technologies into other sectors faces several challenges, requiring the improvement of pre-treatment or purification units. These are concerned with emissions of heavy metals and acids, e.g., Hg, SO2, HCl, and HF. Besides, the circular trend in economy, thinning mineral resources and zero-waste requirement urge the search for reusing wastes of present or past, such as ashes, clays and kaolins. These trends bring openings in using these wastes as adsorbents for CC-U-S and flue-gas purification units.
The research is focused on evaluating lignite combustion fly ash and kaolins as raw materials for cost-effective adsorbents. These are foreseen separately for the purification of flue gases from heavy metals prior to CO2 capture. The adsorbents are synthesized by modification of natural zeolites, kaolin wastes, and synthetic zeolites prepared from fly ash. The latter requires capturing in fabric bag filters of power plants using solid fuel, mainly lignite. The capacity of these adsorbents is evaluated also in respect of CO2 capturing from the flue gas. The flue gases used in the study originate from the combustion of solid fossil fuels, refuse-derived fuels (RDF), and wood-derived biomass.
Experimental units with thermal power output of 500 kW are used in combustion of solid fossil and alternative fuels in fluidised bed at Czech Technical University in Prague, providing the pilot-scale studies in heavy metals and CO2 adsorption in real combustion environment. The flue gas is continuousy analysed for mercury, and the captured fly ash analyses for heavy metals are also mainly focused on malicious mercury. The capacities of newly synthesized adsorbents for heavy metals are compared with the ones obtained with commercially available KBr-modified acitivated carbon, industrially applied in the flue gas treatment. Modification of synthetic zeolite with KBr showed a significant improvement in Hg capture at the pilot device, adding more than 40% to the capacity of non-modified zeolite.
The capacities of newly synthesized CO2 adsorbents were compared with the ones obtained with commercially available Zeolite X industrially applied in the flue gas treatment. The results of experiments with adsorbents derived from geo-polymerised metakaolins demonstrated the capture efficiency similar to the non-modified zeolites A, which is about 30% lower than the one of expensive Zeolite X.
Zeolites synthesized from the lignite fly ash samples at Tallinn University of Technology demonstrated cation-exchange capacities exceeding the one of commercial natural zeolite Zeolith N produced by Evers Anthrazitveredelung e. K., Germany, taken for the reference thus demonstrating an opportunity in production of zeolites capable of effective removal of heavy metals from aqueous media.

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Biography

Sergei Preis, born on May 31, 1959, graduated Tallinn University of Technology (TalTech), Estonia, as Chemical Engineer in 1981 and acquired his doctoral degrees in Environmental and Chemical Engineering in 1988 at TalTech and in 2001 at Lappeenranta University of Technology (LUT), respectively. He worked for TalTech since 1981 till 2000 as Junior Scientist, Senior Scientist, and Head of Laboratory, then for LUT from 2001 to 2014 as Senior Scientist and Associate Professor. From 2015 to 2017 he worked as Chair Professor at South China University of Technology. Since 2018, Sergei Preis is Professor at TalTech, heading the Laboratory of Environmental Engineering. Author of 120 peer-reviewed scientific publications, Sergei Preis successfully supervised ten doctoral studies, having two doctorates under current supervision.