Sulfur, lead, and mercury characteristics in South Africa coals and emissions from the coal-fired power plants

Abstract

Coal-fired power plants (CFPPs) are the dominant source of electricity in South Africa due to coal abundance in the country. However, emissions of SO2, Pb, and Hg have raised serious environmental and public health concerns. Hence, to reduce emissions and utilize coal efficiently, it is essential to estimate emissions trends, understanding existential forms of the elements in coals, and their affinities to minerals, organic matter, and pyrite. Therefore, this paper aimed to assess the forms of elemental occurrence of sulfur (S), lead (Pb), mercury Hg affinities in the coals using statistical correlations and their isotopic compositions. This study also estimated SO2, Pb, and Hg emissions from 1971 to 2018 from the CFPPs based on activity data and emission factors. Based on the results, South African coals mainly comprise equivalent fractions of organic and pyritic S. The Pb were correlated with ash content (R = 0.61), Si, Al, and Ti, which indicates clay mineral-bound Pb. However, the highest Pb206/Pb207 and the lowest Pb208/Pb206 in South Africa coals which contain high inertinite (organic matter) and low S, also reveal organically associated Pb. Similarly, clay minerals linked Hg appeared as of Hg relationship with ash (R = 0.641) and major elements, and the remaining could be an organic matter associated. As an organic matter-associated element least cleanability and readily oxidizing nature, burning South African coals containing a substantial quantity of organic S and organically bound Pb and Hg without washing results in higher emissions. The estimated SO2, Pb, and Hg emissions were 355.84 Gg, 168.91 tons, and 4.17 tons in 1971, and increased to 1468.13 Gg, 696.89 tons, and 17.20 tons in 2018, respectively. The values approximately increased by a factor of 4.