Thermal Properties Study Of Chlorine Salt-Assisted Thermal Desorption Of Mercury From Contaminated Soil

Soil is the basic living guarantee for human beings. As the mercury mining extraction, vinyl chloride production, non-ferrous metal smelting and other industrial processes, soil mercury pollution has become increasingly serious. Based on conventional thermal desorption process, we put forward "Chlorine salt-assisted thermal desorption of mercury from contaminated soil", this method through the way of adding chlorine salt to soil in thermal desorption process to transform HgS、HgO、HgSO4、into HgCl2 or HgCl, which easy to volatilize. By this to reduce temperature and retention time of thermal desorption process.To contrast the thermal volatility of mercury compounds by adding chlorine salt, firstly, thermogravimetric analysis (TGA) associated with MgCl2, CaCl2, NH4Cl,FeCl3 and NaCl respectively was performed to three kinds of inorganic mercury compounds reagents, HgS, HgO and HgSO4. We found NH4Cl and FeCl3 with promoting effect for the three mercury compounds, in the range of 200℃ to 300℃ has obvious weight loss process, further study by XRD analysis of self-made soil contain mercury compounds and chlorine salt indicated the exist of HgCl2 or HgCl, promote the volatilization of HgS, HgO and HgSO4.As follows, explore the influence of chlorine salt handing process on contaminated soil in thermal desorption process. We carried out "wet-stirring-lyophilization" as the optimal pretreatment procedure, compared with chlorine salt directly deal, the total mercury removal efficiency could be improved by more than 10%. After adding chlorine salt to five different sources of pollution soil, we found NH4C1 is suitable for thermal desorption on the soil which polluted by PVC and chlor-alkali production, the total mercury removal rate increased by 16.96%,12.07% and 12.07% in 200℃,1 h, respectively. FeCl3 has wonderful effect on nature mercury area and native mercury mining extraction, which increased by 34.78% and 27.66% by adding FeCl3. With the increase of temperature, residence time, the adventage of chlorine salt-assisted thermal desorption gradually reduced after 200℃,1 h. Total mercury removal rate could be improved by more than 12% after add chlorine salt, mercury salt mud contaminated soil in add NH4Cl more increased by 36.93% after processing.at 200℃,1 h.Again, we studied the white crystals produced by salt-assisted thermal desorption of contaminated soils, through TG and XRD analysis, we confirmed that the products was HgCl2 or HgCl. Finally, By HSC chemistry software AG free energy analysis, we found out that △G (FeCl3)<0 in every reaction, NH4Cl and HgO or HgSO4 react under natural conditions, generate HgCl2, but with HgS responsed after 500℃. NH3 and HgCl2 which created by HgO and NH4Cl can generate HgCl.