Study On Solidification Of MSWI Fly Ash By Cold Sintering

In order to reduce the harm of heavy metals in MSWI fly ash to the environment,this paper uses cold sintering method to solidify MSWI fly ash,studies the influence of doping and process parameters on the leaching concentration of solidified weight metals and material strength,and discusses the mechanism of cold sintering method to solidify heavy metals.Firstly,the influence of cold sintering process parameters on the solidification effect of heavy metals by the original MSWI fly ash was studied,and the best process parameters of cold sintering were determined.The results show that there is an optimal moisture content in cold sintering.With the increase of pressure,temperature and time,the compressive strength and lead curing effect of the solidified body are improved.The best technological parameters of cold sintering solidification of the original MSWI fly ash are temperature 180℃,time100min,pressure 70k N（275MPa）,initial moisture content of the solidified body 20wt%.The high densification of the solidified body and the formation of silicate hydration products provide a guarantee for curing heavy metals and improving the mechanical strength of materials.When 0.2wt%EDTA-2Na or 2wt%Na₂S is added,the heavy metal leaching can reach the landfill standard.Furthermore,the effect of cold sintering method on solidification of MSWI fly ash and the effect of cold sintering method combined with cement and chemical agent on solidification of MSWI fly ash were studied.The results show that the porosity of washed MSWI fly ash increases,the salt content decreases and the calcium content increases.Under the optimal process parameters of cold sintering,the lead leaching concentration of water washed MSWI fly ash solidified body is lower than that of original MSWI fly ash solidified body,but the compressive strength and density are reduced.The compressive strength of washed MSWI fly ash is about 200MPa,the leaching concentration of lead meets the requirements of landfill standard,and the volume of MSWI fly ash solidified by cold sintering method is 49.09%less than that of traditional cement.At last,the feasibility of preparing new building materials of"MSWI fly ash-cement-mineral powder"system by cold sintering method is studied.The results show that the compressive strength of the solidified body with original MSWI fly ash and washed MSWI fly ash is 275.37MPa and 298.59MPa respectively when the mixture ratio is cement 75wt%,10wt%for fly ash and 10wt%for silica fume,MSWI fly ash 5wt%.When the water content is suitable,with the increase of cement content,the compressive strength of solidified body shows an upward trend,while the mineral powder content has the best value,which meets the leaching standard.The formation of hydrated silicate products,such as ettringite,almandine and tobermorite,contributes to the solidification of heavy metals and the improvement of the strength of solidified body.It is feasible to prepare new building materials with low MSWI fly ash content by cold sintering.