Development of low-concentration mercury adsorbents from biohydrogen-generation agricultural residues using sulfur impregnation

Mercury adsorbents were derived from waste biohydrogen-generation barley husk and rice husk via carbonization, steam activation, and sulfur impregnation at 300–650 °C. The samples derived from agricultural residues showed a greater Hg0 adsorption than that of a coal-based activated carbon, confirming the feasibility of resource recovery of these agricultural residuals for low-concentration gaseous Hg adsorption. Sulfur impregnation reduced both the surface area and pore volume of the samples, with lower temperature causing a greater decrease. Elevating the impregnation temperature increased the organic sulfur contents, suggesting that in addition to elemental sulfur, organic sulfur may also act as active sites to improve Hg0 adsorption. Oxygen and sulfur functional groups accompanying the microporous structures may account for the enhancing Hg0 adsorption of the raw and sulfur-treated samples, respectively. The pseudo-second-order model can best describe the chemisorption characteristics, implying that Hg0 adsorption on the samples was in a bimolecular reaction form.

► Feasibility of using agricultural residuals to produce Hg adsorbent was confirmed.
► Sulfur impregnation decreases surface area and pore volume of carbon.
► Sulfur impregnation increases surface active sites for Hg0 adsorption.
► Both physical and chemical properties of carbon are important for Hg0 capture.
► Pseudo-second-order kinetic model best describes Hg0 chemisorption behaviors.