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Selective Removal of Elemental Mercury from High-Concentration SO2 Flue Gas by Thiourea Solution and Investigation of Mechanism

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journal contribution
posted on 29.03.2017, 00:00 by Zhilou Liu, Bing Peng, Liyuan Chai, Hui Liu, Shu Yang, Bentao Yang, Kaisong Xiang, Cao Liu, Dongli Wang
Nonferrous metals smelting industry is a major anthropogenic Hg emission source in China. A new method using transition metal-Tu (thiourea) solution was proposed to selectively remove Hg0 from high SO2 concentration flue gas. It is found that this solution displays significantly high Hg0 removal efficiency, up to above 88.7%, under optimal conditions, whereas the loss of SO2 is only 6.8%. High Tu concentration, low solution pH, and low temperature are helpful for Hg0 removal. The promoting effect of Fe3+ is better than that of Cu2+. The mechanism of selective Hg0 removal was studied by various methods. First, the cyclic voltammetry (CV) curves show that part of Tu could be oxidized to FDS (formamidine disulfide), which could combine with Hg0 to form Hg–Tu complex. Additionally, the UV–vis spectra indicate H2SO3 could improve the stability of FDS and facilitate Hg0 removal. In summary, the use of transition metal-Tu solution to selectively remove Hg0 from smelting flue gas displays excellent efficiency, and the proposed mechanism of Hg0 selective removal is persuasive.