CHARACTERIZATION OF COMMON LIGNITE, XYLITIC LIGNITE AND PYROPISSITE VARIETIES OF LOW-RANK COALS

The chemical characteristics of the organic and mineral constituents o f common lignite, xylitic lignite and pyropissite varieties of Spanish low-rank coals were studied. Chemical analyses showed distinct differ ences in the H and O contents of xylitic lignite and pyropissite: the former is particularly rich in O and poor in H, whereas the reverse is true for the latter. FT-i.r. spectroscopy showed that the organic mat ter of xylitic lignite contains abundant hydroxyl and ether groups whe reas pyropissite is rich in acid/ester and methylene groups. Mineral m atter was characterized by X-ray diffraction and FT-i.r. spectroscopy of low-temperature ash. The main minerals found were kaolinite and qua rtz; illite was detected only in pyropissite. Ca is present in form of carboxylate salts which react during low-temperature ashing with sulf ur and nitrogen oxides, leading to formation of sulfate and nitrate ar tefacts; these species produced the strongest peaks in the X-ray diffr actograms and FT-i.r. spectra of all varieties. Aluminium, relatively abundant in xylitic lignite, is probably organic in origin. In additio n to nine major and minor inorganic elements, 13 trace elements were a nalysed by X-ray fluorescence spectrometry. These trace elements do no t exhibit a specific association with any of the lignite varieties and their concentrations cannot be used as distinguishing characteristics . In contrast, the chemical characteristics of the organic component a llow the three coal varieties to be differentiated clearly.