Evaluation of Nanostructured Sorbents in Differential Bed Reactors for Elemental Mercury Capture

Abstract

Elemental mercury (Hg⁰ ) capture by heterogeneous gas–solid reaction with nanostructured sorbents was studied in a differential bed reactor system at room temperature. Commercially available (four types of iron oxide, titanium dioxide, titania pillared clay) and in-house synthesized (magnetite and SUZ-4 zeolite) sorbents were studied. Elemental mercury capture efficiency greater than 70% was observed for TiO₂, TiO₂ pillared clay (PILC), SUZ-4 zeolite, and one of the commercial iron oxides on irradiation with UV light for an inlet mercury concentration of 75 ± 1.9 μg/m³. The initial rate of Hg⁰ capture per unit mass of sorbent was highest for TiO₂. The initial capture rates, r_init = kS₀ (1-x)C ^α _Hg,0, were determined with α values of 1.03, 1.21, 1.19, and 1.51 for TiO₂, TiO₂ PILC, SUZ-4 zeolite, and one of the commercial iron oxides, respectively. In addition, the rate constants (k) were found to be 2.43×10⁻¹⁷, 4.66×10⁻¹⁹, 3.41×10⁻²⁰ and 8.6×10⁻²⁰μg^1-α m^3α-2 s⁻¹ for TiO², TiO² PILC, SUZ-4 zeolite, and one of the commercial iron oxides, respectively. A three-step sequential extraction technique, targeting surface bound, acid-soluble, and encapsulated mercury species, was used to investigate the binding mechanisms and the mobility of mercury. The mercury associated with one of the commercial iron oxides was more labile than the mercury associated with the other sorbents. Titania (TiO₂) shows the greatest potential to be used as a sorbent to capture elemental mercury on irradiation with UV light based on the results of this study.