Removal of gaseous elemental mercury using seaweed chars impregnated by NH4Cl and NH4Br

Abstract

Enteromorpha is a kind of waste algae that can cause marine ecological disaster. Actively exploring some effective ways for resource utilization of Enteromorpha has important economic and environmental significance. In this article, NH4Cl and NH4Br modified Enteromorpha chars (E8C5 and E8B5) were prepared by pyrolysis and simple impregnation method for capturing gas phase elemental mercury (Hg0) for the first time. The effects of pyrolysis temperature, loading value, reaction temperature and concentrations of main flue gas components (e.g. O2, NO, SO2, H2O) on Hg0 capture were studied. Mercury removal mechanism and kinetics were also investigated. The results show that Hg0 removal efficiency increases with the increase of pyrolysis temperature, and the optimal pyrolysis temperature is 800 °C. Hg0 removal is significantly enhanced by NH4Cl or NH4Br modification, and the chars modified by NH4Br show better performance than those modified by NH4Cl. Optimal loading values and reaction temperature for E8C5 and E8B5 are 5 wt.% and 130 °C, respectively. Presence of O2 and NO promotes Hg0 removal, whereas presence of SO2 inhibits Hg0 removal. Lower concentration of H2O is beneficial to Hg0 removal, but higher concentration of H2O shows an obvious inhibitory effect on Hg0 capture. Hg0 adsorption over E8C5 and E8B5 are endothermic processes. Chemisorption plays a key role in Hg0 removal. Both Hg0 removal processes over E8C5 and E8B5 meet pseudo-second-order kinetic model.