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Increasing Recovery Ratios with an Improved European Community Bureau of Reference Method for Mercury Analysis in Flue Gas Desulfurization Gypsum

Bian, Shuang, Wu, Jiawen, Zhang, Yongsheng, Wang, Tao, Norris, Pauline, Pan, Wei-Ping
Energy & fuels 2018 v.32 no.8 pp. 8340-8347
byproducts, coal, flue gas desulfurization, gypsum, leaching, mercury, power plants, sulfur, trace elements
Coal-fired power plants produce flue gas desulfurization (FGD) gypsum as a byproduct of the sulfur removal process. This gypsum is contaminated with trace elements. Knowing the occurrence and release characteristics of trace elements from the FGD gypsum is very important if the gypsum is to be safely used in different applications. The sequential extraction procedure proposed by the European Community Bureau of Reference (BCR) can be used to provide mercury speciation information for FGD gypsum samples. Many researchers have used the BCR sequential extraction method to analyze the occurrence of mercury in FGD gypsum. Unfortunately, the recovery ratio is low, around 50–60%. The recovery is low because the BCR method does not include the portion of elemental mercury (Hg⁰) lost during each leaching step. In this work, modifications to the BCR method were made to more accurately determine the amount of mercury lost during the extraction. Using this “improved BCR method”, the Lumex RA-915+/PYRO-915 mercury analyzer measures the mercury content in the residues at each extraction step. The difference between the sample and residue concentrations is equal to the amount of Hg released. This indirect measurement method was used to overcome the shortcomings of the traditional BCR sequential extraction process. The results show that the “improved BCR method” has a recovery ratio of about 99%, which can more accurately evaluate the environmental stability of mercury in gypsum. Thus, an improved five-step sequential extraction procedure for analysis of mercury was successfully applied to FGD gypsum samples in this study.