Evaluation of elemental mercury adsorption by fly ash modified with ammonium bromide

Abstract

Coal-fired power plants are significant contributors to the anthropogenic emission of mercury. This study focus on evaluated the methods for modification and preparation of fly ash adsorbent which can be applied to adsorb mercury from power plants. Comparing with isometric impregnation and ion exchange method, it was found that the cost and preparation time of the mechanochemical method significantly reduced. Hg0 adsorption performances of NH4Br-modified fly ashes and subsequent effects of mechanical energy on modifying fly ash were investigated, and the results indicated that increasing mechanical force can make the distribution of bromides to be more uniform and increase the number of surface active sites and groups. Furthermore, Hg0 removal efficiency improved significantly with the increasing bromine loading at 150 °C. There is a positive correlation between mechanical energy on modifying fly ash and subsequently Hg0 adsorption performance. TG/MS analysis was utilized to determine the thermal stability and released material of different samples. Results demonstrated the release of ammonia, which from the modified fly ashes with mechanochemical method, most likely enhances the oxidation and subsequent adsorption of mercury in the 150–200 °C temperature range. All results revealed that the mechanochemical application method for adsorbent preparation on site is competitive on economy, practicability, and mercury removal efficiency.