Mössbauer study of the decomposition of iron-bearing clay minerals during the ashing of five coals

Mineralogy, Chemical Composition, and Microstructure of Ferrospheres in Fly Ashes from Coal Combustion

“…Iron-Bearing Minerals in Fly Ash. The magnetic fractions in fly ashes from coal-fired power plants mainly include ferro-, ferri- and paramagnetic Fe-bearing minerals and phases. ,,,,,, The ferrospheres separated from fly ash normally account for 0.5−18.1% . A large percentage of ferrospheres are commonly 3−20 μm in size (Figure a).…”

“…More than 316 and 188 minerals in coal and fly ash, respectively, have been identified, and most of them are accessory or trace minerals. , XRD (X-ray diffraction) is a very useful technique and one of the most commonly and widely used methods for the identification and characterization of mineral matters in coal and fly ash . Mössbauer spectroscopy is one of the recommended methods for the investigation of fly ashes enriched in iron, and particularly the magnetic and heavy fractions isolated from them. − Iron-bearing minerals in coal and fly ash can also be investigated by scanning electron microscope and an electron microprobe technique. , The characteristics of iron-bearing minerals in the coal and fly ash that were analyzed by Mössbauer spectroscopy, XRD, or similar techniques have been discussed broadly. − Iron in coal is associated with sulfur pyrite (FeS 2 ), and non-sulfur-bearing minerals such as ankerite (CaFe(CO 3 ) 2 ), siderite (FeCO 3 ), and Fe 2+ -illite (clay mineral). ,,,− Iron also occurs as an impurity element in other minerals, such as quartz, kaolinite, boehmite, rutile, and galena. ,− …”

“…Iron-bearing minerals in fly ashes are derived mainly from the decomposition and oxidation of pyrite, siderite, and ankerite in feed coals during combustion process. ,,,,,− ,,, Both dry and wet magnetic separations are effective procedures for isolating some iron-bearing minerals and phases from fly ashes. ,,,,− According to microprobe analysis and XRD as well as Mössbauer spectroscopy investigation, major iron-bearing minerals in fly ashes are ferrispinel (79−90 wt %), represented by complex solid solutions based on magnetite with admixtures of Mg, Mn, and Ca; hematite; and maghemite. ,, The morphology and chemical composition of ferrospheres in fly ashes from coal-fired power plants also have been conducted using optical microscope, FSEM-EDX (filed emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy) and other similar techniques, which were summarized by many researchers. ,,,,− ,− Light-microscopic morphologic appearances of individual coal fly ash particle are correlated with their elemental composition. − And there are morphological differences in different size fractions of ferrospheres in fly ashes . But there is still a lack of systematic interpretation of the morphology of ferrospheres in fly ashes, especially for the fly ash in China's power plants.…”

Methods for Characterization of Inorganic and Mineral Matter in Coal: A Critical Overview

“…This spectroscopy provides useful information on the qualitative and quantitative occurrences of Fe-bearing minerals and amorphous phases in coal. ,,,,,− The Fe 2+ /Fe 3+ ratio, crystal data peculiarities, and solid solutions in Fe-containing coal minerals and phases can also be characterized. For example, these data can be used for a detection of the oxidation and weathering levels of Fe sulfides to Fe 2+ and Fe 3+ sulfates, and later to Fe oxyhydroxides. ,,− Transformations of Fe minerals following other treatments have been studied as well. ,,− The MS has also been proposed as an alternative to wet chemical methods for pyrite analysis in coal. ,,− The application and perspectives of this technique for coal characterization have been recently reviewed …”

“…36,44,[211][212][213][214] Transformations of Fe minerals following other treatments have been studied as well. 148,166,[215][216][217] The MS has also been proposed as an alternative to wet chemical methods for pyrite analysis in coal. 201,210,[218][219][220] The application and perspectives of this technique for coal characterization have been recently reviewed.…”