The relationship between speciation and release ability of mercury in flue gas desulfurization (FGD) gypsum

Multipurpose utilization of flue gas desulfurization (FGD) gypsums releases mercury into environment and poses threats to public health. Determining Hg speciation is essential not only for predicting its toxicity and mobility but also for designing effective remediation strategies. Sequential chemical extraction (SCE) method was used to analyze Hg speciation in this study. The total Hg concentration in four samples ranged from 0.61 to 1.63 μg/g. XRD and EDX analysis revealed that the main chemical composition of FGD gypsum was calcium sulfate (CaSO4). SCE result indicated that Hg was mainly distributed in the strong complex phase, ranging from 60% to 80%. Water soluble mercury in Sample SX accounted for 30% of the total extract, which might be attributed to the relatively high chlorine content in coal. Moreover, the mobility of Hg from FGD gypsum was also investigated in this study, which exhibited biphasic kinetics. The rapid release of Hg was related to the ratio of water soluble Hg at some extent (R2 = 0.818), which signified of more attentions for its stabilization. This study also suggested theoretical framework for the environmental risk associated with FGD gypsum during its usage and disposal.