The fate of selenium in the desulfurization wastewater evaporation process: Migration mechanisms and risk analysis

Owing to the implementation of the zero wastewater discharge policy in China, stricter supervision and technical requirements have been imposed. Hot flue gas evaporation technology exhibits significant advantages in desulfurization wastewater treatment. However, volatile constituents (such as selenium, Se) present in wastewater may be released, thus disrupting the power plant's original Se balance. In this study, the evaporation of three desulfurization wastewater plants is performed. The release of Se mainly begins from the threshold at which wastewater is evaporated to dryness, and Se release rates of 21.5, 25.1, and 35.6% are detected. Furthermore, the key components and properties of wastewater for Se migration are identified through experiments and density functional theory calculations. Lower pH values and Cl^- contents are not conducive to Se stability, and this tendency is more pronounced in selenite. The suspended solid content temporarily traps the Se in the initial evaporation process, as confirmed via a decrease in the Se release rate and a high binding energy (-307.7 kJ/mol). Moreover, results of risk assessment reveal that wastewater evaporation results in a negligible increase in Se concentration. This study evaluates the risk of Se release during wastewater evaporation and provides a basis for Se emission control strategies.