Removal of gaseous elemental mercury by modified diatomite

Abstract

Novel adsorbents with low cost and high efficiency that do not produce secondary pollutants are vital for removing gaseous elemental mercury (Hg0) from coal-fired power plants. In this study, eight diatomite-based adsorbents were developed and used to remove Hg0 in a bench-scale fixed-bed reactor. The effects of active substances, reaction temperature, and gas components on the Hg0 removal performance of diatomite (Dia) and the mechanisms were investigated. After modification, the specific surface area of diatomite increased by 2-to-12 fold, and the Hg0 removal performance was greatly improved. The Hg0 removal efficiencies of the adsorbents decreased in the following order: I-Dia > Br-Dia > Cl-Dia. The Hg0 removal efficiency of CuBr2-Dia reached 91% in the simulated flue gas at the optimal reaction temperature (140 °C). The simultaneous presence of O2 and HCl promoted the Hg0 removal by CuBr2-Dia. NO alone also played a significant role in Hg0 removal. However, SO2 exhibited clear inhibitory effect. The average Hg0 removal efficiencies of CuBr2-Dia were 60% under 1200 ppm SO2, 87% under 1200 ppm SO2 + 300 ppm NO, and 93% under 4% O2 + 1200 ppm SO2 + 300 ppm NO. The changes in the active adsorption sites caused by NO, and those caused by NO + SO2 were different and irreversible. During the Hg0 removal process, Hg0 was oxidized to the Hg2+ or Hg+ species, while Cu2+ and Br radicals were reduced to Cu+ and Br−, respectively.