Study of mercury re-emission in a simulated WFGD solution containing thiocyanate and sulfide ions

In this paper, elemental mercury (Hg0) re-emissions from simulated wet flue gas desulfurization (WFGD) solutions were evaluated in the presence of thiocyanate ions (SCN−) or sulfide ions (S2− and HS−). Experimental results revealed that both thiocyanate ions and sulfide ions could inhibit the reduction of oxidized mercury to Hg0. The inhibition effect of SCN− was mainly attributed to the formation of HgSO3SCN− and HgSCNX−(X–2) (X = 2–4). It was found that the mercury reduction process in the presence of sulfide ions followed different mechanism under acidic or alkaline condition, though the formation of stable HgS could be ascribed to the main inhibition reason. Under acidic condition, the bivalent mercury ions may not directly combine with sulfide ions to form HgS. This had led to a weaker inhibition effect under the acidic condition compared to that under alkaline condition.