Study On The Immobilization Of Heavy Metals In Residues From Microwave Pyrolysis Of Sludge

Along with the increase in production of sewage sludge and the world's energy shortage, Pyrolysis is a clean and efficient processing technology in the field of municipal sludge treatment widely used. During Pyrolysis of sewage sludge, the high temperature achieved can accomplish the decomposition of sludge achieve rapidly and significant reduce the volume. And the energy from the organic components of sludge can be used. This article introduced into the microwave to paralyze sludge, and study on the effect of activated carbon, Fe₂O₃SiC and charry sludge as microwave absorbents on the tenperature. Through leaching experiment and Simulation of acid rain leaching, analyze the immobilization effect of heavy metals in the microwave field. And exploration for immobilization mechanism of heavy metals was done on the basis of analysis of the concentration and distribution in the dry sludge and residues. Meanwhile, the immobilization effect of heavy metals in the conventional pyrolysis residues was studied to compare with the microwave pyrolysis residues.Sludge mixed with different assistants was pyrolyzed in the microwave field, and the results indicated that the temperature of the mixtures could reach up to 800℃. The leaching results of heavy metals with different standard methods showed that it was more effective in TCLP test. The leaching of heavy metals changed as the leaching conditions such as leachant, liquid-solid ratio, pH and the dynamic leaching conditions changed. Cd, Pb, Zn and Cu from the solid of microwave pyrolysis showed a better immobilization effect than the heavy metals from the solid of conventional pyrolysis. The patterns in the distribution of heavy metals in residues from microwave and conventional pyrolysis changed significantly, exchangeable content decreased, residue and Fe-Mn oxide content increased. Unstable state of heavy metal in residues from microwave pyrolysis of sludge decreased by 10%-50%, and the immobilization effect of the same heavy metal considered in different residues was: FeB2BOB3B> AC> Ru> SiC. This was an important reason for the immobilization of heavy metals in microwave field. The distribution and leaching percentage of heavy metal with TCLP in residues indicated the immobilization effect of different heavy metals: Pb>Zn> Cu >Cd. The results of solid residues surface elemental analysis and scanning electron microscopy indicated that a large number of Si, Al accumulated on the surface of solid residues, which have gone through the process of vitrification. Meanwhile solid residues formed smooth compact micro-particles on the surface. The solid residues from microwave pyrolysis of sludge were alkaline. Mixing activated carbon, Ru, SiC and iron oxide as microwave absorbers with wet sludge for the pyrolysis produce the solid residues with pH 11.05, 10.94, 10.89 and 8.58 respectively. Through the studies of heavy metals immobilization effect in microwave pyrolysis of sludge, it can be determined: the change of heavy metals in distribution, the vitrification of solid residues and its strong alkaline made for the immobilization in microwave pyrolysis residues.The immobilization effect and mechanism of the heavy metals during the microwave pyrolysis of sludge was studied in this paper, which supported the aaplication of microwave pyrolysis process with theoretics and technology.