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| Titel |
Thermal characterization of organic matter along a (hypothetical) coalification gradient |
| VerfasserIn |
Ornella Cavallo, Maria Rosaria Provenzano, Claudio Zaccone |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250154000
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| Publikation (Nr.) |
 EGU/EGU2017-19043.pdf |
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| Zusammenfassung |
| Geochemical transformations of organic carbon (C) in aquatic and terrestrial ecosystems are
important starting points for genesis of peats, brown coals and other coal precursors. The
humification process plays a key role in biogeochemical transformations of organic C and, as
a result, in the first stages of coal precursors formation.
Thermal analysis was used by Schnitzer and other scientists since 1950-1960s, in order to
investigate the stability of several organic materials of industrial value including peat
and coal. What soil scientists found was the general occurrence of two exothermic
peaks (exotherm 1 and 2) due to decomposition and combustion reactions of organic
compounds having different thermal stability and, consequently, different degree of
humification.
Thermogravimetric analysis (TG) was carried out on different samples reproducing a
“hypothetical” coalification gradient as follows: peat (IHSS Pahokee peat standard), fulvic
acid (FA), a peat humic acid (HA), leonardite (IHSS Gascoyne standard) and charcoal. An
aliquot of about 20 mg of each sample was heated in a ceramic crucible from 50 to 850˚ C at
30˚ C min−1, at a gas flow rate of 30 mL min−1 using a PerkinElmer TGA4000
thermobalance. Samples were analysed both under nitrogen and under synthetic air. All
analyses were carried out in triplicate and the average coefficient of variation was <1.5%.
Weight losses (in %) were determined within 200-400˚ C (WL1) and 400-600˚
C (WL2) temperature ranges, and the ratio between WL2/WL1 calculated for all
samples. This ratio has been often used as a highly sensitive parameter to describe
chemical changes induced by the bio-transformation of organic materials. Finally, the
temperature at which half of the exothermic mass loss has occurred (TG-T50) was also
calculated.
Preliminary results obtained from TG analysis under air showed that WL2/WL1 ratio was
lower for the FA sample and higher for leonardite and charcoal, following the order
FA<peat∼HA<leonardite<charcoal. When nitrogen was used as gas carrier, a different
stability order to the thermal degradation was obtained, with HF and HA showing a lower
WL2/WL1 ratio (HF<HA<peat<charcoal<leonardite). Anyway, a positive and significant
correlation (p <0.05) was found between WL2/WL1 ratios obtained with both
gases.
TG-T50 was found to be lower for peat and higher for leonardite and charcoal samples
(peat<HA∼FA<leonardite<charcoal) when air was used as carrier gas, whereas, for most of
these matrices, it was not possible to determine this value when nitrogen was used. |
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