固体添加剂对垃圾掺烧污泥焚烧飞灰高温过程中重金属挥发特性的影响

在研究垃圾与污泥掺烧后焚烧飞灰中重金属浸出特征的基础上,重点研究了飞灰在1 000 ℃条件下高温处置过程中重金属(Cu、Zn 、Pb、Cd)随不同停留时间的挥发特性及添加剂(CaO、Al₂O₃、SiO₂、高岭土、粉煤灰)对重金属转化与挥发特性的影响。研究结果表明,飞灰中重金属Zn、Pb、Mn含量较高,Ni的含量较低,而毒性较大的Cd达到29.4 mg/kg。浸出液中七种金属都满足危险废物鉴别标准(GB5085.3-1996),并且重金属的浸出浓度受浸取时间及浸取液pH值影响较大。在同样的高温处置条件下,焚烧飞灰中不同重金属的挥发特性有较大的差别。其中,Pb表现出易挥发的特性,其挥发率超过80%,而Cu挥发性较小,其挥发率小于30%。综合来看,飞灰中重金属的挥发性大小依次为Pb>Cd>Zn>Cu。飞灰中添加Al₂O₃和高岭土可以抑制Cd的挥发,添加Al₂O₃后Pb的挥发率有所减少,添加SiO₂、CaO、高岭土、粉煤灰均使Zn的挥发率降低,而对Cu的挥发率没有抑制作用,这与飞灰中高Cl含量及各痕量元素化合物对固体添加剂活性位选择性的竞争吸附有关。

Effect of solid additive on heavy metal vaporization of fly ash from co-incineration of MSW with sludge at high temperature

On the basis of the leaching characteristics of heavy metals in the fly ash collected from a co-combustion plant of MSW and sewage sludge, the volatilization of heavy metals (Pb, Cd, Cu and Zn) were studied at 1 000 ℃with different residence time. Meanwhile, the influence of solid additive agents (CaO, Al₂O₃, SiO₂, kaolinite and coal ash) was studied. The results show that the contents of Zn, Pb, Mn in fly ash are high, Ni is low and Cd content reaches 29.4 mg/kg. The metals concentrations in leaching solution, changing a great with leaching solution pH and extraction time, meet the hazardous waste identification criteria (GB5085.3-1996).The volatilization of heavy metals has great differences with the order of Pb> Cd> Zn> Cu, in which the volatilization rate of Pb is higher than 80% and that of Cu is less than 30%. In the thermal disposal process, the volatilization rate is influenced by the residence time, and the volatile elements Pb and Cd are particularly evident.The volatilization of Cd reduces after adding Al₂O₃ and kaolinite, and that of Pb reduced after adding Al₂O₃. Zn evaporation rate decreases with adding SiO₂, CaO, kaolinite and coal ash, while that of Cu is not changed. This is related to the high Cl content in fly ash and the competitive adsorption selectivity of the trace element compounds on the active sites of solid additives.