DETERMINATION OF ARSENIC, CADMIUM, MERCURY, STIBIUM, THALLIUM AND ZINC IN COAL AND COAL FLY-ASH

For determination of trace elements in coal by wet chemical methods, the decomposition reaction with nitric acid under elevated pressure was investigated. In the case of carbon-rich fly-ash, it was necessary to add hydrofluoric acid. Treatment for 20 h at about 140-degrees-C was sufficient for complete demineralization and yielded a pale yellow solution. From this, cadmium and thallium were determined by graphite furnace atomic absorption spectrometry (AAS), arsenic and stibium by hydride AAS, mercury by cold vapour techniques, and zinc by flame AAS. Detection limits of 0.1 mug g-1 could be achieved for arsenic, cadmium, stibium and thallium; 0.2 mug g-1 for mercury; and, 5 mug g-1 for zinc. For reasons of comparison the respective trace elements, excluding mercury and thallium, were determined from dry-ashed samples also. In the cases of stibium and arsenic results from dry-ashed samples were lower on average, whereas the results for zinc and cadmium were in the same range. Data for more than 107 coal samples and 26 slag/coal fly-ash samples collected in Austrian coal-fired power plants, were evaluated. Cadmium, zinc and stibium were, on average, higher in the group of slag/coal fly-ash samples than in the coals.