Carbonization and demineralization of coals: A study by means of FT-IR spectroscopy |
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Authors: | V Gómez-Serrano M C Fernández-González M L Rojas-Cervantes M F Alexandre-Franco A Macías-García |
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Affiliation: | (1) Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain;(2) área de Ciencia de Materiales e Ingeniería Metalúrgica, Escuela de Ingenierías Industriales, Universidad de Extremadura, 06071 Badajoz, Spain;(3) Departamento de Química Inorgánica y Química Técnica, Facultad de Ciencias, UNED, 28040 Madrid, Spain |
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Abstract: | Coal basically consists of two parts—a crystalline, inorganic part, and an amorphous, organic part. Based on this, we intended
to study the changes that occurred on the composition and on the chemical structure of coals after carbonization at 1000 or
900° C and demineralization treatments with hydrochloric and hydrofluoric acids. For this, four coals of different categories
(or levels) were chosen: semianthracite (A-O) and high volatile bituminous coal (B-O), which are high level coals, and lignite
(Li-O) and leonardite (Le-O), these being low level coals. The coals were first analysed in terms of their proximate and elemental
compositions and then carbonized and demineralized. Also, the starting coals and the prepared samples were examined by infrared
spectroscopy. In addition, a study of the optimization of the application of this technique for only A-O was carried out.
For A-O and B-O, the spectra recorded intense absorption bands that are ascribable to vibration modes in mineral components
as quartz and aluminosilicates, such as kaolinite. For Li-O and Le-O, the spectra displayed some other bands as well, also
quite intense, which have been assigned to bond vibrations in functional groups and structures of their organic part. The
carbonization of the coals resulted in significant changes in their inorganic part as the content of quartz increased and
the content of aluminosilicates decreased. In addition, the thermal decomposition of mineral carbonates occurred. The carbonization
greatly affects the organic part of the coals, especially in Li-O and Le-O, as most functional groups and structures are not
thermally stable under heating conditions. With regard to demineralization, HF is a more effective agent than HCl, achieving
products with higher organic content. The mass losses are higher in Li-O and Le-O than in A-O and B-O. So, the infrared spectroscopy
allows the analysis of both inorganic and organic parts of the coals and of their carbonization and demineralization products.
These processes facilitate subsequent analysis of the inorganic and organic parts of coals by infrared spectroscopy. In the
application of this technique, both the coal: KBr ratio and the thickness for the disks should be controlled, owing to the
influence on the infrared absorption. |
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Keywords: | Coals carbonization demineralization infrared spectroscopy |
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