Experimental study on the stability of the ClHgSO₃^- in desulfurization wastewater

Wet flue gas desulfurization technologies have received much concern for their superior performance on co-controlling the acid gases and mercury. However, high concentrations of mercury-containing desulfurization wastewater, which discharge from wet flue gas desulfurization system regularly, have received researchers' attention since it might generate the risk of secondary pollution. In this paper, the species of mercuric complexes in the desulfurization wastewater was investigated. It speculated that ClHgSO₃^- might determine the residual rate of Hg²⁺ in the desulfurization wastewater. Besides, the stability of ClHgSO₃^- on the condition of various wastewater features was also evaluated. The experiment revealed that the high temperature and high pH level promoted the decomposition of ClHgSO₃^-. SO₃^2- could restrain the decomposition of ClHgSO₃^- gently; the Hg²⁺ residual rate was determined by the new mercury complexes which compounded by Hg²⁺ and SO₃^2-. The decrease of SO₄^2- and increase of Ca²⁺ concentrations could also stimulate the stability of ClHgSO₃^- in wastewater. Cu²⁺ and Fe²⁺ disturbed the stability of complexes for their catalysis and reduction activities. The study proposed that the ClHgSO₃^- probably decomposes and releases Hg⁰ in two pathways. Furthermore, changes of the water's features could disturb the balance of Hg²⁺-Cl^--SO₃^2- systems, which might stimulate the decomposition of ClHgSO₃.