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REGENERATED HUMIC ACIDS OBTAINED BY THE AIR OXIDATION OF SOUTH MORAVIAN LIGNITE. PART. 2. THERMOANALYTICALCHARACTERIZATION OF PRODUCTS

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Author(s): Zdeněk Cihlář | Jiří Kučerík

Journal: Petroleum and Coal
ISSN 1337-7027

Volume: 52;
Issue: 4;
Start page: 254;
Date: 2010;
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Keywords: lignite oxidation | regenerated humic acids | moisture uptake | thermal degradation.

ABSTRACT
A sample of humic acid prepared from parental lignite and seven regenerated humic acids preparedfrom oxidized ones were extracted from South Moravian lignite. First, the samples were tested fortheir stabilities and degradabilities using thermogravimetry. It was shown that oxidation of lignite instatic reactor at 85 °C produced regenerated humic acids with an increasing content of labile part.The dependency of labile content was exponential-like and reached a constant value after 240 hours ofoxidation. Increasing content of labile part in regenerated humic acids was also confirmed by measuringof heat accompanying the thermo-oxidative degradation using differential scanning calorimetry.The previously reported increase in number of ester bonds and the character of surface of preparedhumic material was evaluated by moisture uptake measurement. Using thermogravimetry, thedetermination of the content of moisture adsorbed on the surface of humic samples after 21 dayswas carried out. In accordance with previous conclusions based on elemental analysis and yield ofregenerated humic acids, the highest moisture content was observed for humic sample prepared influid reactor from lignite oxidized at 50 °C for 72 hours and a sample extracted from lignite oxidized instatic reactor at 85 °C for 456 hours.
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