MERCURY IN COAL - DETERMINATION OF TOTAL MERCURY IN STEAM COALS BY COLD VAPOR ATOMIC ABSORPTION SPECTROMETRY (CV-AAS)

Mercury is one of the most serious and dangerous impurities in the environment globally. It is not biodegradable and all of its forms are described as highly toxic. The combustion of solid fuels remains the major source of anthropogenic mercury and its chemical compounds' emissions. This is the main reason why it is essential to monitor its concentration level. This article presents the method of determining total mercury content in the steam coals delivered by Tauron Wytwarzanie S.A. The study analyzed 17 coal samples from the 13 Polish mines located mainly in the Upper Silesian Coal Basin (USCB). Coals were enriched using classical methods in heavy liquid separators, jigs, heavy liquid cyclone separators, Humphrey's spirals, and by means of flotation. The analytical coal samples were prepared according to the Polish Standard PN-90/G-04502 which includes drying, disintegration, mixing, and reduction of bulk samples. Determination of total mercury in the steam coals was carried out on analytical sample sizes of 0.2 mm. Coals were combusted at 850 degrees C in filtered, dry air (0.5 l/min). The mercury contained in the coals has been atomized and was transformed into Hg-0 vapors, which were analyzed by a mercury analyzer MA-2000, Nippon Instruments Corporation (measuring the range 0-1000 ng, limit of detection 0,002 ng), using cold vapor absorption spectrometry (CV-AAS). The main advantage of this apparatus is its ability to process samples without conducting sample mineralization, and the coupling MA-2000 with autosampler SC-3 which reduces the time needed for a single measurement to 7 minutes. Calibration of the apparatus was carried out by means of the standardization curve method where a polynomial of degree 3 was applied as the type of regression. The correctness of the measurement procedure was verified by means of standard reference materials SRM-2693 and SRM-2692c. Total mercury was detected in coals at concentration levels from 70.3 to 276.4 ppb. The method of determination of total mercury in coals was of good precision where the relative standard deviation RSD equaled 2-10%.