Physicochemical Properties of Fe-Bearing Phases from Commercial Colombian Coal Ash

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.

Trace Elements in Pernik Sub-Bituminous Coals and Their Combustion Products Derived from the Republika Thermal Power Station, Bulgaria

“…In the processes of coal beneficiation and coal combustion in thermoelectric power stations (TPSs), several major waste products are generated, namely coal slurry, associated host rocks, bottom ash, and fly ash. It is well known that the detailed knowledge about the mineralogy and inorganic chemistry of these products has important fundamental, technological [1][2][3][4][5][6][7][8][9], and ecological [10][11][12][13][14][15] significance. Therefore, valuable information on the inorganic composition of coals and their combustion products has been summarized in several monographs [16][17][18][19].…”

Comparison of the Analytical Performance of Inductively Coupled Plasma Mass Spectrometry and Instrumental Neutron Activation Analysis Techniques in the Elemental Analysis of Coal Fly Ash

“…Depending on the origin of the hard coal, ash and other coal combustion residue (CCR) properties can vary significantly both in terms of calorific value and the presence of potential impurities [4,[9][10][11]. Leaching studies should also give some information about the possibilities of potential hazards associated with the extraction of toxic metals and their penetration into the soil and, in turn, into plants and the human food chain [12][13][14].…”

“…Chemical analysis, especially the determination of elements important for their strategic significance and human and environmental safety, is a vital part of scientific research as well as commercial analysis. There are several instrumental methods routinely utilized in determining the minor (0.1-1%) and trace (<0.1%) elements of CCRs: inductively coupled plasma mass spectrometry, ICP-MS; inductively coupled plasma optical emission spectroscopy, ICP-OES; X-ray fluorescence, XRF; and the less commonly used single-element atomic absorption spectroscopy, AAS [9][10][11][12][13][14][15][16][17].…”

Highly Efficient and Magnetically Recyclable Non-Noble Metal Fly Ash-Based Catalysts for 4-Nitrophenol Reduction

“…Regarding catalyst support materials, it is crucial to improve studies based on alternative low-cost materials coming from recycling streams such as coal fly ash (FA), which are mainly composed of aluminosilicate glass and minor amounts of other materials, including Fe-rich particles such as ferrospheres [28,29] that are easily recovered via magnetic separation [2][3][4]. For example, Gadore and Ahmaruzzamn [30] reviewed the use of FA-based nanocomposites as effective photocatalysts for water remediation; Saputra and co-authors [31] prepared a Co-supported fly ash catalyst to promote phenol oxidation and observed a total degradation after 90 min at 45 • C; Yusuff et al [32] used FA-supported ZnO as a catalyst in biodiesel production from used oil and obtained an 83.2% yield after 180 min at 140 • C; Dong et al [33] used coal fly ash as a Ni-Re catalyst support for CO 2 methanation.…”