Performance of Ca(OH)_2-Al_2(SO_4)_3 Addition Method in Removing Boron from Wastewater Discharged from Flue-Gas Desulfurizer

概要

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After supplementing Al2(SO4)3 to wastewater, which was collected from a flue-gas desulfurizer, alkalization by solid Ca(OH)2 or NaOH solution was attempted in order to examine the effect of reaction conditions such as the fed Al2(SO4)3 concentration and the pH of solution on the precipitation of boron in the wastewater. Higher fed concentrations of Al2(SO4)3 into the wastewater resulted in larger amount of boron precipitation. The precipitated boron amount increased with increasing the pH of reacted wastewater solution, and attained the peak or plateau value at the pH in the range of 10-12. The precipitated boron concentrations were in proportion to the precipitated Al(OH)3 concentrations at pH <10 and the precipitated ettringite concentrations at pH >10, respectively. Alkalization by Ca(OH)2, rather than by NaOH, promoted the formation of ettringite to remove boron. It was found that larger the SO4/Al, Ca/Al, and OH/Al for the feed wastewater solution than that of the theoretical values for ettringite promoted the formation of ettringite.
2011-07-01