Physicochemical Properties of Fe-Bearing Phases from Commercial Colombian Coal Ash
Author:
Santos Ana Cláudia1ORCID, Cruz Cláudia1ORCID, Font Eric23ORCID, French David4, Guedes Alexandra1ORCID, Moreira Karen1, Sant’Ovaia Helena1ORCID, Vieira Bruno J. C.5ORCID, Waerenborgh João C.5ORCID, Valentim Bruno1ORCID
Affiliation:
1. Earth Science Institute—Porto Pole, Department of Geosciences, Environment and Spatial Plannings, Faculty of Sciences, University of Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal 2. Department of Earth Sciences, University of Coimbra, 3030-790 Coimbra, Portugal 3. Instituto Dom Luís (IDL), Faculdade de Ciências, Universidade de Lisboa, 1749-026 Lisboa, Portugal 4. School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia 5. Centro de Ciências e Tecnologias Nucleares, DECN, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela LRS, Portugal
Abstract
High amounts of coal combustion products, such as fly ash and bottom ash, are generated every year; however, only 64% are used, which means that a significant part is landfilled despite containing valuable materials such as ferrospheres, which may be used as catalysts, substituting critical raw materials (e.g., platinoids). In commercial coals, pyrite contents are reduced as a pre-combustion S-emissions control measure, so low amounts of ferrospheres are expected in the respective ashes. However, given the large amounts of ash being generated from these coals, it may provide a reliable source of catalysts, with ferrospheres being easily recovered via magnetic separation. Several studies have been conducted regarding these morphotypes; however, there is a lack of investigation considering the ash derived from highly beneficiated coals and the variations with location and time. In this study, bottom ash, economizer grits, and fly ash samples from a Portuguese power plant burning Colombian commercial coal were fractionated using ferrite (Fe-MC fraction) and Nd (Nd-MC fraction) magnets, and a multi-technique approach was used to assess their properties (magnetic parameters, particle size distribution, mineralogy, particle morphology, microtexture, and chemical composition). The Fe-MC presented higher Fe concentrations (up to 44 wt.% Fe2O4) than the Nd-MC (up to 7 wt.% Fe2O4). Once it was a sequential process, Nd magnets essentially collected Fe-bearing aluminosilicate glass, and Fe-bearing minerals were residual when compared to the Fe-MC, where magnetite, magnesioferrite, hematite, and maghemite accounted for up to 30 wt.%. Among the Fe-MC, the sample collected from electrostatic precipitator fly ash (ESP FA), despite having a lower yield, presented higher Fe concentrations than the ones from bottom ash and economizer grits, which was related to the mode of occurrence of Fe-bearing phases: in the Fe-MC from ESP FA, discrete ferrospheres predominated, while in the remaining Fe-bearing phases, they were often embedded in aluminosilicate glass. All Fe-MC samples showed an increase of Fe-substituting elements (e.g., Mn and Ni) and their concentration tended to increase with decreasing particle size along with Fe. The integrated study of cross-sections enabled the identification of oxidation rims, martitization aspects, and the co-existence of hematite and magnesioferrite.
Funder
Fundação para a Ciência e Tecnologia (FCT) and Ministério da Ciência, Tecnologia, e Ensino Superior CHARPHITE of the 3rd ERA-MIN Program 2015 INSUB PhD scholarship FCT support
Subject
Geology,Geotechnical Engineering and Engineering Geology
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