Fe and Co modified vanadium–titanium steel slag as sorbents for elemental mercury adsorption

Abstract

Iron and cobalt modified vanadium titanium steel slag (VTSS) adsorbents Fe(x)–Co(y)/VTSS (with different Fe/Co molar ratios of x/y) prepared by an impregnation method were employed to remove elemental mercury (Hg⁰) from simulated flue gas in a wide-temperature window (150–300 °C). The samples were characterized by XRD, BET, HRTEM, EDS and H₂-TPR. The effects of iron to cobalt molar ratios of x/y, capture temperature, and flue gas components (such as O₂, SO₂ and H₂O) on the Hg⁰ adsorption efficiency were evaluated. The Hg⁰ adsorption mechanisms were proposed by XPS, TG and the pseudo-second-order kinetic model. The results showed that the increase of cobalt amount and the cooperation of Fe and Co promoted Hg⁰ capture. The Fe(3)–Co(3)/VTSS adsorbent exhibited the highest Hg⁰ removal efficiencies of 77.4% within 600 min in 6 vol% O₂ at 300 °C. The presence of O₂ promoted Hg⁰ adsorption. The influence of SO₂ on the Hg⁰ removal efficiency was weak, while the addition of 8 vol% H₂O and 500 ppm SO₂ was found to have a serious inhibition effect. The XPS and TG results showed that the HgO was the major species in the captured mercury, which illustrated that Hg⁰ removal over Fe(x)–Co(y)/VTSS was a catalytic oxidation process. The pseudo-second-order model was demonstrated to simulate the removal of Hg⁰ by Fe(x)–Co(y)/VTSS and the adsorption process is controlled by chemisorption.