Study On Preparation Of Modified Corn Starch And Stabilization Of Heavy Metals In Fly Ash

Waste incineration for power generation has become one of the main technologies of domestic waste treatment.The incineration fly ash generated by waste incineration is a class of hazardous waste（HW18）,which is enriched with various harmful substances such as heavy metals.The research on the harmless treatment technology of incineration fly ash has become an important topic in the field of solid waste pollution control.Among them,the preparation and application of new high efficient organic polymer chelating agent for heavy metals is a hot topic in this field.Based on the physical and chemical characteristics of fly ash incinerated in a waste incineration plant in Hebei province,this paper focuses on the preparation of modified corn starch and its application in chelating heavy metals in fly ash.Modified starch was prepared by reversed-phase emulsion method using corn starch as the matrix.The morphology and structure of modified starch were studied by XRD,FTIR,SEM and other characterization methods.The optimum conditions and effects of adsorption of Pb and Cd in water by modified starch were determined by single factor experiment.The results showed that the maximum adsorption capacity of Pb and Cd for modified starch prepared with 1.0 g acrylamide,3.0 m L methyl methacrylate and 4.0 g acrylic acid reached 155.6 mg·g^-1and 128.5 mg·g^-1at pH 6.7,adsorption time 90 min and adsorption temperature 30℃.The adsorption kinetic experiments show that the adsorption process is more in line with the quasi-primary adsorption kinetics.The isothermal adsorption experiment shows that the process is in good agreement with Langmuir isothermal adsorption model.The multi-factor response surface model fitting analysis was carried out for the adsorption process of Pb by modified starch,and the theoretical optimum adsorption conditions were predicted:The maximum adsorption capacity of Pb was 163.64 mg·g^-1when the pH value was 6.7,the adsorption time was 90min and the adsorption temperature was 30℃for the modified starch prepared with 1.05g acrylamide,3.51 m L methyl methacrylate and 3.75 g acrylic acid.The prepared modified starch chelated fly ash heavy metal was characterized by SEM.The specific surface area of fly ash was larger before treatment,and the particle size of fly ash was significantly increased after modified corn starch treatment,reducing the specific surface area of fly ash.According to XRD characterization of fly ash before and after treatment,the main crystal phases of the two times are Na Cl,Ca CO₃,K₃Na（SO₄）₂and Si O₂.According to the FTIR curves of fly ash before and after treatment,it is indicated that there are mainly carbonate,sulfate and silicaluminate in fly ash.The optimum conditions and effects of modified starch chelating Pb and Cd in fly ash were determined by single factor experiment.The results showed that when the modified starch was 3%,the curing time was 24 h,the liquid-solid ratio was 0.4,and the pH value was 7-9,the leaching concentration of Pb and Cd was the lowest,which was 0.162 mg·L^-1、0.087mg·L^-1,the stabilization rate of Pb and Cd is greater than 93%,and the leaching concentration is far below the limit of the"Hazardous Waste Landfill Pollution Control Standard".The effects of different rainfall environments on the stability of fly ash chelate were studied.The results showed that the slower the rainfall rate,the more the cumulative leaching amounts of Pb and Cd in chelate.When the leaching rate was 5m L·min-1,the cumulative leaching amounts of Pb and Cd were 3.86 mg·kg^-1and 2.55 mg·kg^-1after 16times of leaching.Compared with normal rainfall,the cumulative leaching of Pb and Cd after acid rain was higher,4.76 mg·kg^-1and 3.07 mg·kg^-1,respectively.In acid rain leaching environment,heavy metal leaching is mainly because H⁺continuously replaces heavy metal ions on the surface of chelate particles,which promotes heavy metal leaching.