Abstract
The aim of this study was to develop and examine the morphology and distribution of mercury (Hg) in flue gas desulfurization (FGD) by-product. Mercury in the coal of coal-fired power plants is concentrated in the by-products of desulfurization process, and it is widely used as an additive in cement, building materials and other industries. Due to the different stability of various forms of mercury in the environment, subsequent use of products containing desulfurization by-product additives will continue to be released into the environment, endangering human health. Therefore, it is very necessary to study the form and distribution of mercury in the by-products of desulfurization in coal-fired power plants to provide a theoretical basis for subsequent harmless treatment. For content and morphology of mercury analysis, 1 sample of dry FGD ash and 6 samples of wet FGD gypsum were analyzed. The total 7 samples were extracted using a modification of sequential chemical extractions (SCE) method, which was employed for the partitioning Hg into four fractions: water soluble, acid soluble, H2O2 soluble, and residual. The Hg analysis was done with United States Environmental Protection Agency (USEPA) method 7471B. Comparing with the wet FGD gypsums of coal-fired boilers, the total Hg content in the dry FGD by-product was as high as 1.22 mg/kg, while the total Hg content in the FGD gypsum is 0.23 - 0.74 mg/kg, which was 2 times over the wet FGD gypsum. The concentration of water soluble Hg in the dry FGD by-product was the highest amount (0.72 mg/kg), accounting for 59.02% of the total mercury. While residual Hg content was 0.16 mg/kg, only about 13.11% of the total mercury. Mercury content in FGD gypsum was expressed in the form of ρ (residual Hg) > ρ (H2O2 soluble Hg) > ρ (water soluble Hg) > ρ (acid soluble Hg). The morphology and distribution of mercury in FGD by-products is supposed to be analyzed before utilization, and the impact of mercury on the environment should be considered.
Highlights
Mercury (Hg) is highly toxic, highly volatile, and easy to be enriched in organisms to cause the disease of persistent environmental pollutants [1] [2] [3] [4]
The Hg content in the wet flue gas desulfurization (FGD) gypsum is expressed in the form of water soluble Hg (0.03 - 0.17 mg/kg), acid soluble Hg (0.01 - 0.12 mg/kg), hydrogen peroxide soluble Hg (0.08 - 0.22 mg/kg), and the residual Hg (0.11 - 0.27 mg/kg), which cover the percentages of 13.04% - 25.00%, 4.35% - 17.65%, 27.94% 40.38%, and 29.41% - 47.83 %, respectively
It was assumed that the wet FGD gypsum was safer in utilization, since the total Hg concentration was about 0.23 - 0.74 mg/kg, composing mainly the inert mercury, including the H2O2 soluble mercury and the residual mercury
Summary
Mercury (Hg) is highly toxic, highly volatile, and easy to be enriched in organisms to cause the disease of persistent environmental pollutants [1] [2] [3] [4]. FGD processes are mainly classified as dry desulfurization and wet desulfurization, and the by-products are FGD ash and FGD gypsum . Both can be used as cement additives, road construction material and for soil improvement [7]. The mercury in the process of resource utilization may be released into the environment, which will cause environmental pollution [8]. Evaluation of the mercury speciations and predicting its potential impact on the environment is critical in the disposal of FGD by-products
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