Absorption characteristics of elemental mercury in mercury chloride solutions

Elemental mercury (Hg0) in flue gases can be efficiently captured by mercury chloride (HgCl2) solution. However, the absorption behaviors and the influencing effects are still poorly understood. The mechanism of Hg0 absorption by HgCl2 and the factors that control the removal were studied in this paper. It was found that when the mole ratio of Cl− to HgCl2 is 10:1, the Hg0 removal efficiency is the highest. Among the main mercury chloride species, HgCl3− is the most efficient ion for Hg0 removal in the HgCl2 absorption system when moderate concentrations of chloride ions exist. The Hg0 absorption reactions in the aqueous phase were investigated computationally using Moller–Plesset perturbation theory. The calculated Gibbs free energies and energy barriers are in excellent agreement with the results obtained from experiments. In the presence of SO32− and SO2, Hg2 + reduction occurred and Hg0 removal efficiency decreased. The reduced Hg0 removal can be controlled through increased chloride concentration to some degree. Low pH value in HgCl2 solution enhanced the Hg0 removal efficiency, and the effect was more significant in dilute HgCl2 solutions. The presence of SO42 − and NO3− did not affect Hg0 removal by HgCl2.