Methods for extraction of mercury compounds from coal in Ukraine

Abstract

The ways of prevention of environmental pollution by coal-containing mercury compounds are investigated in the paper. Coal mercury compounds are harmful and toxic impurities. In coal, the mercury is in the form of sulfides and mercury-containing organic compounds. Considerable amounts of native mercury and cinnabar are also recorded. The content of the mercury in terms of metal in the Donbass coal ranges from 0.01 to 1000 g / t. The highest concentrations of mercury compounds are due to hydrothermal and volcanic processes. In Donbass coal, the content of mercury compounds is on average 5 to 10 times greater than the background compared to other coal basins. The most common form of mercury compounds in coal are impurities in sulfide minerals. The content of mercury compounds in pyrite is two orders of magnitude higher than in the organic coal component. It is established that the bulk of the mercury compounds are contained in fine particles. The maximum content is fixed in a fraction of 0.1 - 15 microns. Thus, it can be assumed that the mercury compounds are predominantly contained in the mineral component of coal, which is more intensively ground. It is shown that washing with hot water and the complexing agent solution results in a decrease in the content of mercury compounds in the coal feedstock. The washing solutions become turbid, and this suggests that the mercury compounds are flushed out with fine particles. The increase in the degree of extraction of compounds of the mercury when applying the complexing solution is due to the ability of aurintricarboxylic acid to form complex compounds with the mercury ions. It can be assumed that in this case chemisorption occurs with the formation of complex compounds of the chelate structure on the surface of the particles, followed by dispersion of the particles of the dispersed phase. It was found that washing of the dispersed coal raw material is accompanied by weight loss. This indicates that the mercury compounds are leached from the coal in the form of dispersed particles. Waste sludge is to be disposed of with further disposal.