Saikia, B K and Boruah, R K and Gogoi, P K and Baruah, B P
(2009)
A thermal investigation on coals from Assam (India).
Fuel Processing Technology, 90 (2).
pp. 196-203.
Abstract
A thermal characterization of two coal samples from Ledo and Tikak collieries of Makum
coalfield, Assam, India using XRD, FT-IR, and TGA was reported in this paper. The coal
samples were heated for 20, 40 and 60 min in a 1000-watt heater (temperature ∼250 °C) in
presence of air and characterized by XRD and FT-IR spectroscopy. Both the coals contain
amorphous and crystalline phases. The raw coals also contain very small peaks due to
quartz, calcite, gypsum, pyrite, and chlorite. The XRD patterns were found to change upon
heating. In the coals heated for 20 and 40 min, it was observed that both amorphous and
crystalline parts are common in them; crystalline part being the major one in the 40 min
heated samples. The XRD patterns of the samples heated for 60 min indicate the presence of
major quantities of α-quartz, hematite, and chlorite in them. They also show some new
peaks, which are assigned to be kaolinite, illite, magnetite and very small in comparison to
the amorphous portion in raw coals. α-quartz was found to be most stable crystalline phase
of silica in the coals. The crystallinity % (X-ray) of the coals heat-treated for different times
was determined and found to be increasing with time of heating. The FT-IR spectra of raw
and heat-treated coal samples at 250 °C were also recorded and compared. The spectra were
observed to be almost similar and it was observed that few functional groups disappear on
heating at 250 °C. The same coal samples were also characterized by thermogravimetric
analysis (TGA) and differential thermal analysis (DTA) techniques. On heat treatment in
air atmosphere up to 800 °C, 20–27% weight loss occurs due to removal of various
volatile materials. DTA results indicate the chemical reactivity of the coal sample initially
at 80–110 °C due to loss of water, and two other major reactions at around 420 and 530 °C
due to primary and secondary volatization.
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