| Waste incineration power generation has become one of the main technologies for municipal solid waste(MSW)treatment in China,but the fly ash produced after incineration is rich in heavy metals,which is classified as the hazardous waste.In China,the management of fly ash is mainly through "solidification/stabilization+landfill disposal",i.e.,after solidification/stabilization treatment,fly ash can be landfilled in municipal solid waste landfills after meeting the landfill criteria.However,the single cement solidification and chelating agent stabilization have some limitations,and the long-term landfill process is easily affected by many factors(such as rainfall,soluble salt),which makes heavy metals easier to migrate to the surrounding environment.Therefore,the purpose of this experiment is to optimize the solidification/stabilization process of fly ash,and to explore the effects of different rainfall environments and soluble salts on the stability of fly ash solidified body,the main contents and results are as follows:The process optimization of fly ash solidification/stabilization treatment was studied.The results showed that the optimal process parameters of cement+chelating agent solidification/stabilization treatment were as follows:20%cement,2%DTC dosage,liquid-solid ratio(mL/g)as 0.4,and the leaching concentrations of Pb and Cd in solidified body was 1.07 mg/L and 0.14 mg/L,respectively The results showed that the optimal process parameters of washing pretreatment were as follows:washing with CO2 for 10 min,liquid-solid ratio of washing for 10:1,and the elution mass of Pb and Cd in fly ash were 9.42 mg/kg and 5.70 mg/kg respectively.The leaching concentration of Pb and Cd in the solidified body is 0.95 mg/L and 0.09 mg/L respectively,and the treatment efficiency is 51.3%and 95.3%,respectively.The effect of different rainfall environment on the fly ash solidified body stability was studied.The results showed that:the slower the rainfall rate,the more Pb cumulative leaching in the solidified body.When the eluviating rate is 5 mL/min and after 16 times,the cumulative leaching amount of Pb is 3.86 mg/kg;Compared to the normal rainfall,the leaching level of heavy metals in acid rain environment was higher.After 12 times of acid rain eluviating,the cumulative leaching amount of Cd was up to 0.70 mg/kg,the exchangeable fraction increased from 1.0%to 13.5%,the proportion of other forms decreased,and the residual form were decreased from 46.6%to 42.0%.In normal rainfall environment,the leaching of heavy metals is mainly controlled by leaching and carbonation nucleation.In the acid rain leaching environment,the leaching of heavy metals is mainly affected by H+,which continuously replaced the heavy metal ions on the surface of the solid particles,resulting in to increase of the leaching of heavy metals.The effect of soluble salt on the stability of fly ash solidified body was studied.As a result,it is found that the presence of soluble salts can reduce the stability of the fly ash solidified body.After the rainfall cycles,the raw fly ash solidified body has a higher level of heavy metal leaching than the water-washed fly ash solidified body.The cumulative leaching amount of Pb and Cd in the raw ash solidified body was 5.57 mg/kg and 1.19 mg/kg,respectively.The cumulative leaching amount of Pb and Cd in the fly ash solidified body was 2.47 mg/kg and 0.59 mg/kg,respectively;The change of heavy metal fractions in the original ash solidified body was larger,among which the exchangeable state and carbonate binding state of Cd and Pb increased from 3.5%to 16.8%and 12.1%to 21.2%,respectively. |
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