Disposal of wastewater from wet flue gas desulfurization (FGD) systems is a major concern for coal-fired power plant industry. According to a USEPA report in 2009, most of the high metal (Ca2+, Mg2+, Na+) and halide (Cl-) concentrations involved in waste from power plants occur in FGD systems and discharge of these wastewaters can have negative environmental impacts. Therefore, USEPA released the final revision to the Steam Electric Power Effluent Limitation Guidelines in 2015, regulating the discharge limits for many pollutants in FGD wastewater (FGDWW) and other processed water. One potential pathway being explored to manage FGDWW is the zero liquid discharge strategy which involves reducing the volume of the FGDWW by concentrating to brine, and then mixing the brine with concrete or fly ash and other chemical additives to form a stabilized paste suitable for landfill disposal. This process is called brine solidification and encapsulation (SE) technology. The brine SE technology has shown to be a viable treatment process for sequestrating heavy metals in solid form, but has not been very efficient in immobilizing halides, because of the high solubility and elevated concentrations of halides in concentrated brine. The broad motivation of this project is to improve halide sequestration in the fly ash-brine paste by substituting halides and sulfate in cementitious hydrates to form AFm and AFt phases. Halides can be encapsulated in these cementitious systems when anions like chloride interact with high aluminate cementitious materials to form mineral phases including, Friedel’s salt, Kuzel’s salt etc. The objective of this study is to synthesize AFm and AFt phases in the laboratory using reagent-grade chemicals, to characterize and measure the solubility of the phase minerals. The first part of the study involves synthesis, characterization, and determination of the solubility constant (Ksp) of Friedel’s salt (FS). A factorial design was implemented to identify the variables that influence the formation of FS, including the reaction temperature, atmospheric conditions, and Ca/Al ratio. The structure and morphology of the synthesized samples was examined using thermogravimetric analysis (TGA-DSC), x-ray diffraction and scanning electron microscopy (SEM-EDS). Using these optimized operating variables, further synthesis of FS will be performed using field raw materials such as fly ash and wastewater brine

Synthesis of AFm and AFt phases to sequester halides from flue gas desulfurization (FGD) wastewater

256th National Meeting (2018)

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