Characterizing the mechanisms of gas-phase elemental mercury adsorption with iodine-impregnated activated carbons using Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure analysis

We developed a series of activated carbons (ACs) for gas-phase elemental mercury (Hg-0) removal via the impregnation of potassium iodide (KI), ammonium iodide (NH4I), potassium iodate (KIO3), and KI, followed by CuSO4. The pore structure and surface chemistry of the ACs were characterized using Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure analysis (XANES). All sorbents exhibited excellent Hg-0 removal efficiencies of 97.2-99.9% in the following order: AC-KI + CuSO4 > AC-NH4I > AC-KIO3 > AC-KI > AC-virgin. The results revealed that there was no Hg-0 in any spent sorbent, including the virgin AC, indicating that chemisorption by the ACs was the dominant Hg-0 removal process in this study. Carbon and oxygen atoms in the ACs, as well as O-2 in the carrier gas, were considered to participate in the chemical reactions responsible for Hg-0 removal. Despite the use of different impregnation precursors, the main form of Hg adsorbed by the impregnated ACs was estimated to be HgI2. Molecular I-2 was identified by XANES in AC-KI + CuSO4, AC-NH4I, and AC-KIO3. Triiodide (I-3(-)) was detected by both XPS and XANES in all impregnated ACs and may serve as the I-2 donor, consequently promoting chemisorption.