Study on mercury desorption from silver-loaded activated carbon fibre and activated carbon fibre

Abstract

Both silver-loaded activated carbon fibre (silver-loaded ACF) with the silver content of 14.07% and activated carbon fibre (ACF) in form of sheet shape were tested to get their saturation adsorption capacities for mercury in a nitrogen stream. The results show that silver-loaded ACF and ACF have a saturation adsorption capacity of 192.3 mg/g and 29.4 mg/g at 70°C, which is 48–192 and 7–29 fold that of common activated carbon, respectively. The thermal desorption characteristics of elemental mercury of the two sorbents were investigated by thermogravimetric analysis (TGA). Mercury desorption from silver-loaded ACF occurred in the temperature range of 100–650°C. The mercury desorption efficiency is 94.73% as temperature increases from 50 to 650°C within 70 min. Mercury desorption from ACF occurs at 100–230°C, and mercury desorption efficiency is 69.93% as temperature increases from 50 to 350°C within 40 min. Both silver-loaded ACF samples undergoing mercury adsorption and thermal desorption run were analyzed by scanning electron microscope (SEM). After mercury adsorption, the silver enriches in silver amalgam particles and intensively distribute on the junctures of ACF microcrystals. And after thermal desorption, the enriching silver gets to dispersedly distribute on the surface of ACF in form of globular particles in submicron-size or nano-size. The SEM micrographs of ACF after mercury adsorption and thermal desorption run show that the elemental mercury by physical adsorption disappear, but mercuric oxide particles by chemical adsorption has a little increase. It suggests that elemental mercury can easily be removed by thermal treatment but mercuric oxide cannot be removed. Parts of elemental mercury might transform to mercuric oxide during thermal desorption.