Reduction of Divalent Mercury to Elemental Mercury by Fe- and Ni-Based Reductants

Abstract

The conversion of divalent mercury to elemental mercury using a solid reductant is the advanced technology of the mercury continuous emission monitoring system (Hg-CEMS). This work proposed new iron-and nickelbased reductants. In the fixed-bed experiments, the reductant carriers were screened and the effects of temperature, preparation parameters, and flue gas components on the efficiency of HgCl 2 reduction were investigated. The results show that SiO 2 has no effect on Hg 0 and does not adsorb Hg 2+ , which satisfies the requirements of the reductant carrier. The reduction efficiency of both Fe/ SiO 2 and Ni/SiO 2 exceeds 90% at 400 °C, and their reduction efficiency increases to almost 95% under the optimum parameters of active component to carrier molar ratio of 2 and particle size of 8−20 mesh. Nevertheless, HCl, O 2 , and NO in the flue gas have some negative impacts on the reduction efficiency of Fe/SiO 2 and Ni/SiO 2 because they react with the active components Fe and Ni and inhibit the conversion of Hg 2+ to Hg 0 . However, SO 2 and CO 2 basically have no effect on the Hg 2+ reduction performance of the two reductants.