Temperature stability of mercury compounds in solid substrates

Abstract

Abstract:The major aim of the newly adopted Mercury Convention is to reduce global mercury (Hg) emissions to the environment. In high temperature industrial processes, including coal combustion, Hg compounds present as impurities in solid materials are decomposed and evaporated leading to the emission of Hg to the atmosphere. The behaviour of different Hg compounds and their mixtures during heating have been the subject of numerous studies, and is the topic of the present work. Controlled heating can be used to fractionate Hg compounds in solid substrates, offering the possibility of identification and quantification of Hg compounds. In the attempt to develop a method for temperature fractionation of Hg, experiments were conducted with pure Hg compounds, and the compounds mixed with different substrates (SiO 2 and CaSO 4 • 2H 2 O), for calibration purposes. Detection was performed by two methods, namely Cold Vapour Atomic Absorption Spectrometry (CV AAS) with Zeeman background correction, and Nier-type Mass Spectrometry with a Knudsen cell (MS). Further investigation is in process.

Desorption kinetic study of mercury species in spent mercury chloride catalyst from polyvinyl chloride production process

“…The second reaction corresponding to the temperature range from 436.15 K to 694.15 K, is the thermal desorption of Hg and HgCl 2 , and the mass loss is 13%. According to the former researches [30][31][32][33], the desorption temperature range of the mercury and mercury compounds is from 323.15 K to 613.15 K, while this temperature range is lower than that in this work, and the reaction temperature difference might be caused by different sample compositions and structures. In this work, the matrix of the spent catalysts is activated carbon.…”

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

“…The first peaks can be attributed to the decomposition of the HgF 2 , while the second peak, at 440˚C, corresponds to HgO decomposition as described later (Figure 4(d) (Figures 4(a)-(c)), appearing at temperatures of around 670˚C, are difficult to explain since no theoretical background exists. We assume that this is caused by the experimental set up in which ionic Hg could have been deposited on the cooler surfaces of the inner wall of the tubing and finally released by high temperature gas flow towards the end of the temperature cycle [51]. This may be confirmed by the good mass balance observed during the experiments ( Table 4).…”

“…Thermograms for pure Hg chlorides and bromide are identical (Figures 4(a)-(c)), while that for pure HgF 2 differs significantly (Figure 4(d)), with several overlapping peaks between 200 and 370˚C and one strong peak at 440˚C [51].…”

“…Pure Hg(I) sulfate (Figure 5(a)) shows a larger peak at 300˚C and a second at 520˚C, while Hg (II) sulfate (Figure 5(b)) exhibits only one major peak at 540˚C [51]. According to a report [55] this is a result of a multistep decomposition of Hg(I, II) sulfates.…”

“…The reason for similar patterns of thermograms for Hg 2 Cl 2 and HgCl 2 lies in Hg(0) and HgCl 2 having the same vapor pressure [16]. At higher temperatures, Hg 2 Cl 2 follows a decomposition step, described in Equation (1) where, as a result, two peaks are released (Hg(0) and HgCl 2 ) [34] [52] [53], emerging at the same temperature due to the same vapor pressure [51]. At the same temperature HgCl 2 compound also decomposes, following the decomposition step shown in Equation (2).…”