Characteristics and Inhibition of Hg0 Re-emission in a Wet Flue Gas Desulfurization System

Characteristics of Hg0 re-emission in a wet flue gas desulfurization (WFGD) system were investigated on the basis of a bubble column. Five addition agents were used to inhibit Hg0 re-emission and improve removal of gaseous mercury. The results show that SO32– plays an important role in Hg0 re-emission in a WFGD system. Hg0 re-emission is intensified sharply in the presence of SO32– and further intensified with the increase of the SO32– concentration. Hg0 re-emission is strengthened at a higher temperature of desulfurization slurry. However, the removal efficiencies of both Hg2+ and total gaseous mercury decrease significantly with an increasing slurry temperature. The decreasing amplitude of total mercury removal efficiency is slightly higher than that of Hg2+. In addition, the re-emission rate of Hg0 declines first and then increases with an increasing pH value. A least Hg0 re-emission is observed at a pH value of 5.5. Fenton reagent, NaClO, K2S2O8, Na2S, and ethylenediaminetetraacetic acid (EDTA) can inhibit Hg0 re-emission to different extents. Among them, Fenton reagent and EDTA exhibit better performance than that of NaClO and Na2S. The least inhibition effect is found for K2S2O8. For the sake of effective inhibition of Hg0 re-emission and gaseous mercury removal, a lower slurry temperature, a pH value in the range of 2.5–3.5, and a Fe2+ concentration of 50 mg/L are optimal in a practical WFGD system.