Metaxas Α., Georgakopoulos Α., D. Karageorgiou, G. Papanikolaou, and E. Karageorgiou, “CO2 CONTENT OF GREEK LIGNITE: THE CASE OF PROASTIO LIGNITE DEPOSIT IN PTOLEMAIS BASIN, NORTHERN GREECE”, geosociety, vol. 43, no. 5, pp. 2274–2283, Jan. 2010.