Thermogravimetric and XRD study of the effects of chloride salts on the thermal decomposition of mercury compounds

In this paper, the effects of chloride salt (MgCl2, CaCl2 or NaCl) addition on the thermal decomposition of five inorganic mercury compounds (HgCl2, HgS, Hg(NO3)2·H2O, HgO, and HgSO4) were investigated by thermogravimetric analysis. Mercury-contaminated soil samples collected from Inner Mongolia were used to verify the results. The desorption temperatures of the mercury compounds increased in the following order: HgCl = HgCl2 < HgS < Hg(NO3)2·H2O < HgO < HgSO4. Among the chloride salts, MgCl2 had the greatest effect on thermal desorption of the mercury compounds, with the greatest reduction in the initial temperature of thermal desorption. After MgCl2 treatment, the mercury removal rates for the soil were 65.67–81.35 % (sample A), 70.74–84.91 % (sample B), and 69.08 % (sample C). The increase in the mercury removal rate for sample C with addition of MgCl2 was particularly large (34.96–69.08 %). X-Ray diffraction analysis of white crystals from the thermal desorption with MgCl2 indicated that MgCl2 promoted conversion of the mercury compounds in the soil to mercury(II) chloride and dimercury dichloride. This transformation is beneficial for applying thermal desorption to remedy mercury-contaminated soils and treat of mercury containing waste.