Laboratory Study on Mercury Release of the Gypsum from the Mercury Coremoval Wet Flue Gas Desulfurization System with Additives

In this study, the mercury release of the gypsum from the mercury coremoval wet flue gas desulfurization (FGD) process with post-thermal treatment or open-stack disposal was investigated experimentally. The results indicated that the aqueous-phase oxidized mercury could be efficiently captured and stored in the solid-phase gypsum by using the additives like NaHS, DTCR, and TMT. However, it could be found that the thermal stability of the mercury species on the resulting gypsum decreased significantly under typical wallboard-manufacturing conditions. Especially, 92.8% of mercury was released from the DTCR-treated sample. The following thermal decomposition tests further confirmed this result. The mercury ions in DTCR-Hg compounds were linked to more sulfur atoms, which were ready to transfer electrons to nearby mercury ions during heat treatment, resulting in its lower stability. It could be also seen that the thermal stabilities of mercury species decreased with an increasing amount of additives. Moreover, the mercury leaching tests showed that additives addition could lead to an evident increase in the mercury leaching content, and the mercury leaching content increased on the order of Hg-TMT < beta-HgS < Hg-DTCR All these results suggested that more attention should be paid toward the mercury release during the post-treatment and disposal of wet FGD gypsum from the mercury coremoval wet FGD system by using additives.