Study on the mercury captured by mechanochemical and bromide surface modification of coal fly ash

•Mercury adsorption was improved by coupled mechanochemical and bromide modification method.•Mercury capture increased with increased grinding time initially and then stabilized.•Improvements in mercury capture performance are due to both physical and chemical factors.•More grinding produces smaller particles and exposes more unburned carbon.

Power plant coal fly ash was modified for mercury adsorption. The fly ash was subjected to mechanochemical ball milling and bromide compounds were added. The results show that mercury capture capacity increased with increasing grinding time, up to 50 min. Grinding over 50 min did not lead to further improvements. Results from the mercury adsorption test show that the mechanochemical processing technique coupled with the addition of bromide compounds improves mercury adsorption performance for fly ash. Both physical and chemical factors contribute to the improvements in capture performance. Increasing the grinding time produced smaller particles with higher surface area. As a result, more unburned carbon was exposed, which resulted in better mercury adsorption. Thermal gravimetric analysis of modified fly ash shows combustion peak temperatures shift towards lower temperatures with increased grinding time. This result indicates that mechanical treatment increased the thermal activity of fly ash. As a result of this study, the first on-line modified fly ash unit was installed on site at a 300 MW coal fired power plant in China.