Res. Chem. Intermed.
, Vol. 33, No. 8–9, pp. 825–839 (2007)
Also available online - www.brill.nl/rci
Groups of paramagnetic centres in coal samples with
different carbon contents
and ANDRZEJ B. WI ˛ECKOWSKI
Institute of Coal Chemistry, Polish Academy of Sciences, Sowi´nskiego 5, 44-121 Gliwice, Poland
Division of Magnetic Resonance Spectroscopy, Institute of Physics, Faculty of Physics &
Astronomy, University od Zielona Góra, Szafrana 4a, 65-516 Zielona Góra, Poland
Received 1 May 2006; accepted 7 June 2006
Abstract—Complex systems of paramagnetic centres existing in demineralised ﬂame coal (71.4 wt%
C), medium-rank coal (85.6 wt% C) and anthracite (94.9 wt% C) were analysed by electron para-
magnetic resonance spectroscopy (EPR). Different groups of paramagnetic centres were searched in
macerals (exinite, vitrinite, inertinite) of coals with carbon contents of 73.8 wt% C and 85.6 wt% C.
Experimental EPR spectra were ﬁtted by different superposition of theoretical lines. Total concentra-
tion of paramagnetic centres both in coal and macerals increases with carbon content in the sample.
Total concentration of paramagnetic centres in macerals increases from exinite to inertinite. Four
groups of paramagnetic centres were found in medium-rank coal, and only two groups exist in ﬂame
coal and anthracite. The EPR spectrum of medium-rank coal is a superposition of two broad and two
narrow lines. Both broad and narrow, and two narrow lines were measured in EPR spectra of ﬂame
coal and anthracite, respectively. Two types of paramagnetic centres with broad lines and one group
with narrow lines exist in exinite and vitrinite from medium-rank coal. Two narrow components were
observed in EPR spectra of its inertinite. Two different broad electron paramagnetic resonance signals
were detected for macerals from low-coaliﬁcated coal. Paramagnetic centres systems of medium-rank
coal samples reveal the most complex character. Broad EPR lines were not observed for the higher
coaliﬁcated samples, i.e., anthracite and inertinite from medium-rank coal. Narrow lines do not occur
in EPR spectra of low-coaliﬁcated macerals. Strong dipolar interactions and fast spin-lattice relaxation
processes are characteristic for paramagnetic centres with broad lines. Strong exchange interactions
and short spin-lattice relaxation time were measured for paramagnetic centres with the narrowest EPR
Keywords: Electron paramagnetic resonance; paramagnetic centres; coal; macerals.
To whom correspondence should be addressed. E-mail: A.B.Wieckowski@proton.if.uz.zgora.pl