Experimental data from a laboratory-scale wet scrubber simulator confirmed that oxidized mercury, Hg{sup}(2+), can be reduced by aqueous S(IV) (sulfite and/or bisulfite) species and results in elemental mercury (Hg{sup}0) emissions under typical wet FGD scrubber conditions. The S(IV)-induced Hg{sup}(2+) reduction and Hg{sup}0 emission mechanism can be described by a model which assumes that only a fraction of the Hg{sup}(2+) can be reduced, and the rate-controlling step of the overall process is a first-order reaction involving the Hg-S(IV) complexes. Experimental data and model simulations predict that the Hg{sup}(2+) in the flue gas can cause rapid increase of Hg{sup}0 concentration in the flue gas across a FGD scrubber. Forced oxidation can enhance Hg{sup}(2+) reduction and Hg{sup}0 emission by decreasing the S(IV) concentration in the scrubbing liquor. The model predictions also indicate that flue gas Hg{sup}0 increase across a wet FGD scrubber can be reduced by decreasing the pH, increasing S(IV) concentration, and lowering the temperature.
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