Partitioning And Speciation Transformation Of Heavy Metals Cu, Ni, Zn During Municipal Solid Waste Incineration

Incineration has become an important method of municipal solid waste (MSW) management with the economic development and population growth. However, the resulting environmental problem has become a hot topic in society, especially the emissions of heavy metals and dioxins. In our country, the content of heavy metals in MSW is high. If the emissions are not constrainted, heavy metals will accumulate in the environment, and thus serious secondary pollution is produced. In addition, Cu in fly ash is an important catalyst for the formation of dioxins, so it has a high risk of environmental pollution.Because of the complexity of the MSW, this thesis consideredthe physical components, chemical composition and traces elements, and then gave the simulation solutions of MSW containing heavy metals. Based on layer burning grate technology, we designed the tube furnace burning experimental system. According to US EPA Method 5 and Method 29, we established a laboratory sampling standard. Based on the soil standards, digestion methods of Cu, Ni and Zn were determined by examining indicators of recovery. The content of Cu, Ni and Zn were quantitatively detected using ICP-AES. The inhomogeneous and heterogeneous thermodynamic equilibrium model was established by using Gibbs free energy minimization. Considering the characteristics of MSW in China, experimental research and theoretical analysis on the partitioning and speciation behaviors of Cu, Ni and Zn during MSWI were carried out in this thesis, and following results were obtained.Firstly, the effects of the chlorine species, chlorine content, temperature, and incineration time on Cu, Ni and Zn partitioning and speciation were investigated. Both the organic chloride (PVC) and inorganic chloride (NaCl) could effectively react with Cu, Ni, Zn to form chlorides with low melting and boiling points (CuCl, NiCl2 and ZnCl2, enhancing the heavy metal partition in fly ash and flue gas. Temperature and pyrolysis characteristics of chlorine had synergistic effects on the partitioning and speciation of heavy metals. With the increase of temperature, the effects of PVC on Cu chloration decreased, while the chloration of Ni and Zn enhancement. When the temperature exceeded the melting point of NaCl, heating helped to enhance mass transfer of liquid phase NaCl, and promoted the chloride and volatile. Incineration time had no significant influence on PVC, but NaCl was significantly affected.Next, the effects of the sulfur species, sulfur content, temperature, and sulfur and chlorine coupling effects on Cu, Ni and Zn partitioning and speciation were studied. Sulfur tended to react with Cu, Ni and Zn to form nonvolatile sulfate, and with the temperature decreases the sulfate become more stable. Sulfide (Na2S) and sulfate (Na2SO4) could promote bottom ash molten, thus inhibiting the evaporation characteristics. Sulfur could effectively promote inorganic chlorine decomposition, releasing more chloric acid, and enhance the volatility. Sulfur and chlorine coupling effects was significantly affected by temperature. The evaporation rate at 800℃ is much higher than 900℃ and 1000℃. The effect of Na2S and Na2SO4 coupling with chlorine was much lower than the sulfur, but the evaporation rate decreased because of the molten.Then, the influence of moisture on Cu, Ni and Zn partitioning and speciation was investigated. The moisture in flue gas was mainly affected by Cl and HC1, chlorinated and hydrolysis reaction equilibrium shift. However, the moisture in MSW was mainly affected by combustion characteristics. With the increase of moisture content in MSW, the ignition, extinguishing and burning-down periods were prolonged, and also the highest temperature was substantially increased.Finally, the effects of inorganic substances, Al2O3, SiO2, and CaO on Cu, Ni and Zn partitioning and speciation were investigated. During the action of PVC, Al2O3 couldsignificantly reduce Cu, Zn volatilization ratio; SiO2 reduced evaporation ratio of zinc to some extent; Al2O3 and SlO2 had minimal effect on the nickel. During the action of NaCl, Al2O3 and SiO2 could promote the oxidative decomposition of NaCl, resulting in a significant increase in Cu, Ni, and Zn volatilization ratio. In the removal of acid, CaO could reduce the Cu, Ni, and zinc volatilization ratio. Meanwhile, CaO could also react with Al2O3 and SiO2 to form stable aluminosilicate, and significantly reduce the NaCl effect of chloride.The findings of this thesisenhanced the understanding of heavy metals behaviors during MSWI in China and provided valuable information for the improvement of incineration furnace design and the development of heavy metals control technologyies.