垃圾焚化飛灰中揮發性重金屬之移動特性

Mobility characteristics of volatile heavy metals in municipal solid waste incinerator fly ash

何鴻哲(Hong-Che Ho)

指導教授 ： 高思懷

淡江大學/工學院/水資源及環境工程學系博士班/博士(2008年)

https://doi.org/10.6846/TKU.2008.00690

摘要

垃圾焚化飛灰不論採固化掩埋處置或熱處理再利用，其重金屬之溶出特性與熱處理之蒸發特性，均為必須嚴重關切的問題。飛灰中重金屬之溶出特性與蒸發特性除本身之化學組成外，亦受環境之pH值或周邊化合物特性之影響。本研究之目的主要在探討旋風集塵灰與袋式過濾灰兩種飛灰中，四種重金屬（鉛、鋅、銅及鎘）的溶出與熱處理時之移動特性。
飛灰重金屬之溶出行為主要依毒性特性溶出程序（TCLP）進行，並討論飛灰粒徑及鹼度對重金屬溶出行為之影響；重金屬之熱移動特性則藉管狀燃燒爐進行，並配合水洗前處理釐清氯鹽在重金屬蒸發過程所扮演之角色；此外磷酸穩定對重金屬之溶出及蒸發的作用，在研究中亦有所探討。
由溶出實驗結果得知，旋風集塵灰之TCLP可符合法規之限值，即使提高其鹼度或降低其粒徑可使重金屬鉛之溶出量增加，但仍可符合溶出標準。袋式過濾灰中鉛之溶出濃度則明顯超過限值，添加少量磷酸予以穩定化後，則可有效抑制鉛之溶出，同樣地，使用適量之硫酸與硝酸，使TCLP溶出液之pH值落於10-12範圍內，亦可使各重金屬之溶出濃度降至最低。
兩種飛灰於熱處理時，鉛均為最易蒸發之重金屬之一，且袋式過濾灰經水洗前處理後，鋅、銅及鎘之蒸發率均大幅降低，但鉛之蒸發趨勢則未受影響，顯示鉛為飛灰中最具移動性之重金屬。此外，研究中亦證實，袋式過濾灰中所含之高量氯化物（如氯化鈣）在重金屬之蒸發特性中扮演了相當重要的角色，在熱處理過程中，可將飛灰中之重金屬氧化物轉化為氯化物而加速其蒸發，且其對氧化鉛之轉化作用明顯優於氧化鋅，具有一定之順序性。至於磷酸穩定後之袋式過濾灰及水洗灰，其重金屬蒸發率似無明顯變化，就重金屬之熱移動特性而言，其穩定效果有限。

關鍵字

焚化飛灰 ； 重金屬 ； 溶出 ； 蒸發 ； 磷酸穩定

並列摘要

Leaching and evaporation characteristics of heavy metals in Municipal Solid Waste Incinerator Fly Ash (MSWIFA) should be considered seriously during solidified for landfill or thermal treatment for recycling. These characteristics of heavy metals in MSWIFA are affected by the species of metals and the conditions of surrounding, such as pH and chemical components. In this study, leaching and thermal mobility of four selected heavy metals (Pb, Zn, Cu and Cd) found in two types of MSWIFA [cyclone ash (CA) and filter ash (FA)] were investigated.
Leaching behavior of heavy metals from MSWIFA was investigated by toxicity characteristic leaching procedure (TCLP). The effect of particle size and alkalinity of fly ash on leaching behavior were also discussed in this study. Thermal behavior of heavy metals from MSWIFA was performed with tube furnace. The role of chloride in MSWIFA during heavy metals evaporation procedure was investigated by water washing pretreatment. In addition, the influence of phosphoric acid stabilization on heavy metals leaching and evaporation was also explored in this research.
While reducing the particle size or/and increasing the alkalinity of CA elevate the leaching concentration of Pb, the leaching concentrations of Pb, Zn, Cu and Cd in CA meet the regulatory limit of TCLP in Taiwan. However, the leaching concentration of Pb in FA fails to the regulatory limit. Lead leaching concentration was restrained by blending FA and 2-3 M phosphoric acid with liquid/solid ratio=0.5 ml/g. Similarly, FA blending with sulfuric acid or nitric acid result in the pH of TCLP leachate 10-12 also inhibits the leaching concentration of heavy metals.
Lead possesses the highest evaporation ratio among the examined heavy metals in the two types of fly ashes under thermal treatment. While FA washed with water removes large amounts of chloride in FA and is able to inhibit the evaporation ratio of zinc, copper and cadmium significantly, it still has no effects on lead. It is experimentally concluded that chlorides play a key role in the determination of the evaporation of heavy metals in the fly ashes. That is, chloride salts in fly ashes will transform metal oxides into metal chlorides and enhance the evaporation ratio of heavy metals significantly. Furthermore, there is a selectivity of the transformation of chloride salts so that lead oxide has higher priority than zinc oxide. FA and water washed filter ash (WWFA) stabilized by phosphoric acid show no significantly variance in evaporation ratio of selected heavy metals.

並列關鍵字

incinerator fly ash ； heavy metals ； leaching ； evaporation ； phosphoric acid stabilization

參考文獻

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