Synthesis of Layered Double Hydroxides to Sequester Halides from Flue Gas Desulfurization Wastewater Concentrate

Hypersaline brines like flue gas desulfurization wastewater concentrate are difficult to treat because of high halide concentration and currently, there are a lack of cost-effective and energy-efficient technologies for the removal of halides. This research explored the feasibility of removing halides from high-salinity brines through the precipitation of layered double hydroxides. Parameters that affect the reduction of the concentration of halides including, the initial molar concentration of halides, the calcium to aluminum ratio, and reaction temperature were evaluated. The stability of the layered double hydroxide products at various prevailing solutions and environmental conditions were investigated and optimal calcium to the aluminum ratio for the effective removal of the halides was established. Experimental results confirmed that the initial halide concentration, rather than the calcium to aluminum ratio, highly influenced the mass of halides sequestered in the structure of the layered double hydroxide samples. It was also observed that the layered double hydroxide samples undergo congruent dissolution when mixed in water or basic solutions, while dissolution rates in acidic solutions were high with little residues remaining. Based on the analyses from characterization using various instrumentation and the statistical analyses, it could be hypothesized that the synthesis of layered double hydroxides using calcium to aluminum ratio of 3:1 will be optimal for effective removal of halides from hypersaline solutions. This research will lead to a better understanding of the formation of layered double hydroxides while it contributes to the evaluation of key controlling variables will provide a framework to treat field samples like real and complex FGD wastewater concentrate. In addition, the results suggest that this process is simple, low-cost, and an effective method to treat high-salinity brines.