THE CONTENT OF RADIOACTIVE ELEMENTS IN THE POLISH LIGNITE AND ITS ASHES

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7105-98-8 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 11, 597-604 pp, DOI: 10.5593/sgem2017/11/S01.075

ABSTRACT

All the elements in the periodic table from polonium to uranium belong to the group of radioactive elements. Additionally, potassium isotopes (40 K) should also be included to the mentioned group. A number of studies have shown that coal has a moderate ability to concentrate radioactive elements, but this problem becomes more important in the case of coal ash, where the accumulation of these elements takes place. This is associated with the low volatility of uranium and thorium, of which only a small amount is released during the combustion of coal. The analysis of the variability of radioactive properties was conducted by examining the concentration of uranium, thorium, and radioactive potassium in coal and ash, the radioactivity (γ) of these elements, and calculating the f1 condition. On the basis of statistical analysis, it has been found that the analyzed content of radioactive elements in coal and ashes was characterized by a very high variability. In the examined samples, the average Th content is 2.33 ppm and ranges from 0.2 ppm to 10.8 ppm, while in the ashes it is between 0.90 and 38.60 ppm with an average value of 7.69 ppm. The majority of samples contains up to 2 ppm of thorium, while its distribution is characterized by a distinct right-hand skewness. Generally, the examined coal ash contains up to 10 ppm of Th. Uranium (235U, 238U), similarly to thorium, is another radioactive element that is easily absorbed by coal. The average content of this element in coal and the earth’s crust is 1.0-1.6 ppm and 6.0 ppm, respectively. Its content in the analyzed coal is 0.11-7.44 ppm while in the ash this value ranges between 0.4 and 53.20 ppm. The average share of uranium in the examined samples is 1.48 ppm for coal and 5.73 ppm for ash. The average content of radioactive isotope 40K in coal is 0.004 ppm, while in ash this value amounts to 0.23 ppm. The radioactivity of 40K is virtually undetectable in both ashes and coal because its share in the total activity of these materials is negligible. Lignite from the examined deposits meets the requirements of the "f1" condition, with the highest values (recorded in the Turów deposit) not exceeding 0.40 pCi/g. Significantly higher values of this ratio, in the range from 0.02 to 2.46 pCi/g, can be found in coal ash samples. This suggests that in the case of the samples from the one deposit the condition of radioactivity (γ) below 1.25 pCi/g is not met and these ashes can be dangerous for the natural environment.

Keywords: lignite, radioactive elements, ash, combustion