垃圾焚烧中氯化物对重金属Cd迁移转化特性的影响

采用管式炉和模拟垃圾对垃圾焚烧中氯化物对重金属Cd迁移转化特性的影响进行了研究,使用ICP-AES(美国EPA消解方法)、SEM、EDS和XRD分析技术对重金属浓度、灰渣表面形貌、成分和灰渣X射线衍射物相等进行了分析.结果表明,氯化物的加入均使得97％以上的Cd分布于飞灰中,且随氯化物含量的增加在飞灰中的分布逐渐增加.有机氯PVC和无机氯NaCl含量的变化对Cd迁移分布的影响没有显著差别.PVC对Cd迁移分布影响受温度影响显著,550℃时Cd在飞灰中分布为80.51%,850℃时Cd在飞灰中的分布上升为97.91%,但在温度超过CdCl₂的熔点568℃后温度的影响较小.NaCl对Cd的迁移分布受温度影响不明显,加入NaCl后550℃时Cd在飞灰中分布为95.02%,1 000℃时在飞灰中的分布为96.58%.氯化物存在下停留时间对Cd迁移分布没有显著影响.底渣和飞灰的SEM/EDS和XRD分析表明,PVC和NaCl对Cd迁移转化作用机理不同.

Effects of chlorides on Cd partitioning and speciation in a simulated MSW incinerator

The effects of chlorides (including inorganic chloride NaCl and organic chloride PVC) on Cd emission in MSW (municipal solid waste) incineration was investigated using a simulated tubular furnace and the simulated MSW spiked with heavy metals. The concentrations of heavy metals were measured by ICP-AES after the digesting of samples including bottom ash, fly ash and flue gas according to related USEPA Methods. Heavy metal species in bottom ash and fly ash were identified by X-ray diffraction technique and the spectra of elements distributed and micrographs of bottom ash and fly ash were detected by energy dispersive X-ray system and scanning electron microscope, respectively. The results indicated that the emission of Cd tended to be enhanced with the increasing of chloride content, and 97% Cd partitioned in fly ash after spiked chlorides. However, the content effect of inorganic chloride NaCl and inorganic chloride PVC on Cd emission had no significant difference. The effect of PVC on Cd partitioning was affected by temperature, 80.51% Cd partitioned in fly ash at 550 degrees C and 97.91% Cd partitioned in fly ash at 850 degrees C, when temperature went above the melting point of CdCl2 (568 degrees C), the effect of temperature became less important. The effect of NaCl on Cd partitioning was not affected by temperature, 95.02% Cd partitioned in fly ash at 550 degrees C and 96.58% Cd partitioned at 1 000 degrees C when spiked NaCl. Residence time had no significant effect on Cd partitioning with spiked chlorides. The two different mechanisms of chlorides effects on Cd emission were identified by bottom ash and fly ash analysis using SEM/EDS and XRD technique.