Mercury removal from flue gas by magnetospheres present in fly ash: Role of iron species and modification by HF

Abstract

The Hg0 removal capacities of magnetospheres from fly ash collected from different power plants were investigated at a wide temperature range of 100–400°C. The relationship between Hg0 removal efficiency (ηT) and iron content/species of magnetospheres was investigated. The magnetospheres attained the optimal Hg0 removal capacity at 250°C. The reaction temperature played an important role in Hg0 adsorption and oxidation behaviors. At low reaction temperature (100°C and 150°C), the adsorption of Hg0 played a predominant role in Hg0 removal, while the Hg0 removal mainly depended on the Hg0 oxidation capacity at high temperature (200–400°C). The Hg0 removal capacity increased with the increase of iron content. The percentage of ferrospinel and hematite in magnetospheres is a key factor for determining the Hg0 removal capacity as well. Hydrogen fluoride (HF) could remove the glass-phase materials on the magnetospheres and the active iron species embedded in the glass phase could be exposed and accessible. After fluorinated by HF, the Hg0 removal capacity increased in different degree for different magnetospheres, which depended on the content of active iron species in raw magnetospheres.