城市生活垃圾焚烧飞灰重金属的浸出特性

LEACHING BEHAVIOR OF HEAVY METALS FROM MSWI FLY ASH

对用流化床焚烧炉混烧垃圾和煤的布袋飞灰进行了重金属的TCLP(ToxicityCharacteristicLeachingProcedure)浸出特性实验,探讨了液固比、初始pH值及浸出时间对飞灰中重金属Pb、Cr、Cd、Ni、Cu、Zn的浸出影响。结果表明,重金属的浸出量都随着液固比的增加而增加,其中Cr、Cu一般呈上升趋势,Cd、Ni、Zn在液固比大于20时曲线变化较平缓,Pb的浸出规律比较特殊,有一个明显的波峰和波谷。重金属在浸取液的pH≤2 90时的浸出浓度远远大于pH≥4 03时的浸出浓度。Pb、Cr、Zn随着浸出时间的增加,浸出浓度下降,而Cd、Ni上升,Cu是先上升后下降。在液固比、初始pH值及浸出时间这三个影响因素中,pH值对重金属的浸出影响较大,重金属在酸性环境下较易浸出。

TCLP experiment has been performed to study the relationships between liquid-to-solid ratio (L/S), initial pH value, extraction time and leaching characteristics of heavy metals (Pb, Cr, Cd, Ni, Cu, Zn) in fly ash from a coal and MSW(municipal solid waste) co-firing fluidized bed incinerator. The results suggest that the leaching weight of heavy metals increases with the rise of L/S, in which the leaching weight of Cr and Cu increases in most cases, but the leaching weight of Cd, Ni and Zn changes slightly when L/S exceeds 20. The leaching behavior of Pb is special, for its leaching curve has obviously a wave crest and a wave hollow. The leaching concentration of heavy metals at initial pH≤2.90 is larger greatly than that at initial pH≥4.03. With the increase of extraction time, the leaching concentration of Pb, Cr and Zn decreases, but that of Cd and Ni increases in general. The leaching concentration of Cu increases first, and then reduces. Among the three factors which are L/S, initial pH and extraction time, the effect of initial pH on heavy metals leaching is the largest. Heavy metals leaching from fly ash is more easily in acidic liquor than in basic liquor.