The Research On MSWI Fly Ash Characteristics And Chelation Stabilization/Cement Solidification Of Heavy Metals

The incineration of MSW(MSWI)has become one of the important MSW disposal in China,the harmful substances such as heavy metals in the fly ash produced by MS WI will cause damage to the environment.The fly ashes of MSWI are quite different due to regional,seasonal and other factors in China.The methods such as cement solidification and chemical stabilization have some limitations when dealing with fly ashes,it is difficult to formulate economical and effective treatment scheme according to the characteristics of fly ash.It's necessary to study the characteristics of MSWI fly ash and the effect of treatment,then the fly ash can meet the standard of safe landfill.This paper focuses on the analysis of the physical characteristics of the fly ash,heavy metal pollution characteristics of fly ash and the compressive strength of the solidified body which produced in many regions and seasons in China.The influence of cement curing and chemical stabilization on the treatment of heavy metals in fly ash and the influence of different factors on the compressive strength of the solidified body were compared.The percentage of moisture of MSWI fly ash is low and strong alkaline.Fly ash particles are generally fine and the surface is concave and convex,and there are a lot of holes between particles which makes fly ash has strong adsorption.It is mainly composed of oxides and aluminosilicate of Ca,Si,Al,K,Na,Fe and other elements which have certain cementitious activity.At the same time,it also contains a small amount of heavy metals.Ni,Cu,Zn,Cd and Pb are the most common elements in fly ash.Generally,the treated fly ash is massive block or agglomerate,the percentage of moisture increases and color deepens,the hydration products can be observed and the leaching concentration of heavy metals is decreased obviously,the chemical forms of heavy metals shift to more stable forms during processing.The chemicals have a certain effect on the stability of heavy metals in fly ash,and the removal effects of different chemical on different heavy metals have difference.The more cement added,the better the treatment effect of fly ash.The treatment of chemical stabilization has better effect on Cd.The cement solidification method is more suitable for Pb and Zn.Advantages can be combined with stabilization and solidification,the method has a stable effect on the heavy metals,and in the case of same dose chelating addition,the synergistic stabilization effect of DTC with cement is better than TMT with cement.The compressive strength of different fly ash is quite different,with the increase of curing age,the compressive strength increases.And the lower the water-cement ratio,the better the curing effect,generally the 7d curing age is fine.The compressive strength of solidified body decreases with the erosion of landfill leachate,the compressive strength decreases as the soaking time increases.After prolonged curing time,the anti-erosion ability of the solidified body to leachate was improved.The higher the compressive strength,the less the leaching amount of heavy metals in the fly ash.