Study on speciation of HgCl2 supported over activated carbon in simulated flue gases by temperature-programmed decomposition desorption mass spectrometry

•HgCl2 was supported over activated carbon by an HCl solution method.•Reactivity of HgCl2 over activated carbon with Hg, SO2 and H2S was investigated.•HgCl2 was sublimated when it was pretreated with Hg-H2O.•Some HgCl2 was converted to HgS and HgO after pretreatment of HgCl2 with H2S-H2O. HgCl2 that was homogenously dispersed over activated carbon was prepared by an HCl solution method (HgCl2(HCl)/AC), in the present study. The speciation of HgCl2(HCl)/AC in simulated flue gases was further investigated by a temperature-programmed decomposition desorption mass spectroscopy method, to clarify its transformation mechanism. It was found that HgCl2 sublimation occurred after Hg-H2O pretreatment, evidenced by the disappearance of the desorption peak of HgCl2 at 80 °C. After Hg-H2O pretreatment, new species of HgCl2 were formed, as confirmed by similar peak intensities of HgCl2 at mass numbers 270 and 272 at 335 °C. The SO2-H2O or H2S-H2O pretreatment helped stabilize the HgCl2 species supported over the AC, as evidenced by the weaker desorption peak of HgCl2 at around 80 °C. For the HgCl2(HCl)/AC pretreated with SO2-H2O, four desorption peaks of mercury were found, at 280, 335, 380 and 480 °C, indicating that new mercury compounds were formed during pretreatment or the TPDD process. The mercury desorbed at 280 °C was derived from a mercury complex of [HgCl]2SO4⋯A-C, while the mercury desorbed at 480 °C resulted from HgSO4. Some HgO species might be formed and stabilized over the AC during the TPDD process, corresponding to two mercury desorption peaks at 335 and 380 °C. After the pretreatment of HgCl2(HCl)/AC with H2S-H2O, some HgCl2 were transformed to HgS and HgO species, as evidenced by the mercury desorption peaks at 280, 305 and 380 °C.