Characterization Of MSWI Fly Ash And Synergistic Disposal With Landfill Leachate

Municipal solid waste (MSW) fly ash is one of hazardous solid wastes because of itshigh concentrations of heavy metals, dioxin and other pollutants content. At present indomestic MSW fly ash processing is mainly used sanitary landfill method and the fly ash needspecial treatment before landfill. However, large land areas are acquired while landfilled andthe environmental security problems such as landfill leachate and heavy metal leakage areoccurred. Therefore, further research on physicochemical property of MSWI fly ash andeffective disposal technology of fly ash are necessary.Firstly, fly ash was sieved into six different particle size, The results showd that the flyash particle size distribution approximate a normal distribution, about70%of the fly ashparticle size concentrated in the38.5⁷5μm, the proportion of fly ash that particle size lessthan38.5μm and greater than450μm is very small,6.3%and2.9%respectively. Severalcharacterization methods were used to investigate the fly ash characteristics, the resultsshowed that the main components of fly ash in all particle size were CaO, ZnO, K₂O, Na₂O,Al₂O₃, MgO, Fe₂O₃, Cl, SiO₂, SO₃and P₂O₅. The Cl content of fly ash increases withdecreasing particle size, whereas SiO₂content increased as the diameter increases. Moreover,the results indicated that the smaller the fly ash particle size, the larger the specific surfacearea.Secondly, the heavy metals distributions in fly ash with different particle size werestudied. It was noted that volatile metals such as Zn and Pb were higher than other difficultvolatile metals. The content of Cu, Zn, Pb and Cd decreases with the particle size decreaseand increases when the particle size increased. When the fly ash particle size was less than125μm, water soluble fraction of Pb is accounted for42%of total content of Pb. The heavymetals in small particle size were higher except Ni and Cr.The concentrations of weak acid soluble and reducible fractions of Cu, Zn and Cd werehigher. The soluble Pb was the highest. The results indicated that special attention should bepaid on those heavy metals that easy dissolved in acidic and neutral leaching conditions.Residue phase were the main fractions of Ni and Cr, which had less potentially impact on theenvironment.Finally, the synergistic disposal of fly ash using concentrated landfill leachate rejectedfrom reverse osmosis (RO) based on above in-depth knowledge of the physical and chemicalproperties of fly ash were studied. The change characteristics of landfill leachate and MSWIfly ash were investigated. The results indicated that the removal rate of TDS, ammonia nitrogen and soluble phosphate were significantly after the concentrated landfill leachate passthrough the fly ash column, which demonstrated the significant phosphorus removal wasmainly occurred by chemical precipitation reaction rather than the pore surface adsorption.After reaction a period of time, the phosphate removal efficiency could reached100%. As theexperimental session progresses with the column test processing, most of heavy metalconcentrations increased firstly and then decreased. The fly ash had significant changes ofmineral phase and functional groups after column test. The XRD data showed that thediffraction peaks of KCl and NaCl disappear and diffraction peaks of CaCO₃became strongerafter the column experiments.