碳酸化对不同碱度飞灰中重金属的长期影响

通过对不同地区生活垃圾焚烧飞灰进行碳酸化处理，采用XRF，SEM以及XRD分析飞灰理化特性，通过pH值测定、重金属浸出实验以及重金属形态分析探究CO₂对不同焚烧飞灰中超标重金属Zn、Pb、Cd的长期影响研究.结果表明，由于焚烧过程中烟气排放限值降低需喷入大量氢氧化钙等脱酸剂，导致焚烧飞灰呈现不同碱度特性.根据醋酸缓冲溶液法浸出实验后的飞灰浸出液pH值，将飞灰分为“酸灰”与“碱灰”，并对两类飞灰进行长期碳酸化实验.对比碳酸化前后飞灰中重金属的浸出毒性，“酸灰”中重金属浸出毒性远大于“碱灰”，但是碳酸化处置后“酸灰”中重金属Zn、Cd的浸出浓度分别降低10%~18%和9%~30%；“碱灰”中重金属Zn和Cd的浸出浓度显著增大，且浸出浓度最大超过《生活垃圾填埋场污染控制标准》的1.46与63.2倍；碳酸化对“酸灰”与“碱灰”中的两性重金属Pb的浸出不具有规律性，但总体而言，碳酸化对“碱灰”中重金属Pb的影响更大.最后通过BCR连续分级提取法分析碳酸化前后飞灰中重金属形态的变化规律，碳酸化后，“酸灰”中重金属Zn、Cd的浸出浓度受到T4赋存占比增加的影响呈下降趋势，但部分样品中T1赋存占比有增加现象，说明此类重金属仍存在浸出风险，而“碱灰”碳酸化后重金属Zn、Cd的浸出浓度受到T1赋存占比增加的影响呈增加趋势.因此在填埋处置前应重点关注不同碱度飞灰中的重金属浸出特性，为飞灰长期稳定填埋提供保障.

Long-term effect of carbonation on heavy metals in fly ash of different alkalinity

Through carbonation treatment of domestic waste incineration fly ash in different areas, and the physical and chemical characteristics of fly ash are analyzed by XRF, SEM, and XRD, then the long-term impact of CO₂ on the excessive heavy metals of Zn, Pb and Cd in different incineration fly ash is studied by pH measurement, heavy metal leaching experiment and heavy metal speciation analysis. The research shows that the incineration fly ash displayed different alkalinity characteristics due to the reduction of flue gas emission limits in the incineration process, which required a large amount of deacidification agent such as calcium hydroxide. According to the pH value of the leaching solution after the acetic acid buffer solution leaching experiment, the fly ash is divided into "acid ash" and "alkali ash", and the long-term carbonation experiments are carried out. The results showed that the leaching toxicity of heavy metals in "acid ash" was much higher than that of "alkali ash", but the leaching concentration of heavy metals Zn and Cd in "acid ash" after carbonation are reduced by 10%~18% and 9%~30% respectively. The leaching concentration of heavy metals Zn and Cd in "alkali ash" increased significantly, and the maximum leaching concentration exceeded 1.46 and 63.2 times of the standard for pollution control on the municipal solid waste incineration. The leaching of amphoteric heavy metal Pb in "acid ash" and "alkali ash" is not regular after carbonation, but in general, carbonation has a greater effect on heavy metal Pb in "alkali ash". Finally, the change law of heavy metals in fly ash before and after carbonation is analyzed by BCR sequntial extraction procedure. The BCR results show that the leaching concentration of heavy metals Zn and Cd in "acid ash" shows a downward trend affected by the increase of the proportion of T4after carbonation, but the proportion of T1in some samples increases, which indicated that such heavy metals still have leaching risk. However, the leaching concentration of heavy metals Zn and Cd in "alkali ash" shows an increasing trend affected by the increase of the proportion of T1after carbonation. Therefore, we should focus on the leaching characteristics of heavy metals in fly ash with different alkalinity before landfill disposal, and provide guarantee for long-term stable landfill of fly ash.