| The incineration of domestic waste produces a large amount of fly ash containing high concentrations of heavy metals and chloride salts.Taking the waste incineration fly ash(hereinafter referred to as fly ash)of a renewable energy company as the research object,the atomic analysis absorption spectrophotometric method is used to analyze the heavy metal elements(Pb,Cd,Mn,Ni)in the domestic waste incineration fly ash(hereinafter referred to as fly ash).The content and morphology of fly ash were studied by scanning electron microscopy(SEM),X-ray diffraction(XRD)and other methods to characterize and analyze the fly ash.The effects of ultrasound and biochar on the leaching characteristics of fly ash were studied.Under the condition of 30℃ and different liquid-solid ratio,60%-70%of chlorine in fly ash can be removed by washing,but the leaching rate of heavy metals is lower than 10%,so the leaching effect is not obvious.After treatment,the proportion of weak acid in the extracted state of heavy metals in fly ash decreased,while the content of other forms did not change significantly,and the total amount of heavy metals in fly ash increased.The effects of ultrasonic frequency,ultrasonic time and liquid-solid ratio on heavy metal leaching rate,morphology distribution and chloride ion leaching concentration in fly ash were studied.The results showed that when the ultrasonic frequency was 20 KHZ,the heavy metal leaching rate did not change much compared with the washing rate.When the ultrasonic frequency was 100kHz and 20+100kHz,the heavy metal leaching rate was significantly increased.After treatment,the proportion of weak acid extracted from heavy metal in fly ash increased,the proportion of reducing or oxidizing state decreased,and the proportion of residual state increased slightly.After 20+100kHz dual-frequency ultrasonic washing,the leaching rate of chloride ion reached 75.51%.The loss reduction rate of fly ash reaches 50%-60%.The effects of pH,leaching time and liquid-solid ratio on the leaching characteristics of fly ash were compared using hydrochloric acid as the leaching agent.The results showed that the pH of the reaction system directly affected the leaching rate of heavy metals.The content of chloride ion in fly ash after pickling treatment(>6.60mg/g)was higher than that of washing.After treatment,the extracted and residual states of fly ash weak acid increased,and the reducible and oxidizable states decreased.The reduction rate of fly ash is 66%-93%,and the reduction of fly ash is obvious.The effects of ultrasonic frequency,pH of reaction system and liquid-solid ratio on the leaching characteristics of fly ash were studied by ultrasonic-hydrochloric acid leaching.The results showed that the proportion of heavy metal residue increased significantly compared with pickling at 20+100kHz ultrasonic frequency.After ultrasound-assisted acid leaching for 4h,the leaching yield of fly ash chloride ion was higher(>4.8mg/g)than that of the original ash chloride ion.The loss reduction rate of fly ash is 85%-95%,slightly higher than pickling.Finally,the fixation of heavy metals in fly ash by straw biochar was studied.The effects of biochar addition amount,fixed time,liquid-solid ratio on heavy metals and chloride leaching in fly ash were studied.It was found that the leaching amount of heavy metals from the straw biochar mixed with the fly ash was less than 15%,which fixed the heavy metals in the fly ash.After mixed treatment,the chlorine ion content of fly ash is low,close to the application limit of ordinary cement,and the co-treatment of heavy metals with biochar is more feasible.Figure[26]table[21]... |
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