Temperature Fractionation (TF) of Hg Compounds in Gypsum from Wet Flue Gas Desulfurization System of the Coal Fired Thermal Power Plant (TPP)

Abstract

Gypsum from the wet flue gas desulfurization system of the lignite fired thermal power plant Sostanj, Slovenia, can efficiently retain mercury (Hg), of which most is contained in finer gypsum fractions, with concentrations above 10 kg -1 . The aim of this work was to identify and study the temperature stability of Hg species in gypsum by a temperature fractionation (TF) method. A self-constructed apparatus was used that consisted of an electrical furnace for controlled heating up to 700°C, with a heating rate of 2.2°C·min -1 , and an AAS detector with Zeeman background correction. The pattern of Hg release during temperature increase depends highly on the matrix/substrate in which it is contained. Based on spiking gypsum with known Hg compounds we concluded that the largest proportion of Hg in gypsum belongs to Hg-Cl and Hg-Br compounds appearing at 160°C to 200°C, followed by smaller amounts of HgO, HgS and Hg sulfates appearing at 300°C and 450°C. Further development of methodology for identifying Hg species would require identification of the decomposition fragments of Hg and other compounds, complemented by a better understanding of Hg reactivity at higher temperatures.