開發一個適合評估焚化爐底渣資源化之焚化再生粒料金屬溶出潛勢之方法

Development of a suitable method for assessing the heavy metal leaching potential of incinerating recycled aggregate from bottom ash

呂建志(Chien-Chih Lu)

指導教授 ： 林逸彬

國立臺灣大學/工學院/環境工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802219

摘要

焚化再生粒料是以焚化爐底渣為原料，經再利用機構以破碎, 分選,水洗、熟化等前處理而成，在台灣受環保署訂定之「垃圾焚化廠焚化底渣再利用管理方式」管理，這些焚化再生粒料經固定頻率之毒性特性溶出試驗(TCLP)後，若符合再利用標準，可以作為建材使用。此外，部分焚化再生粒料會以水泥製成混凝土使用，試圖更進一步增進其環境相容性。TCLP是根據樣品的酸鹼值，以pH 4.9或2.9的醋酸溶液作為萃取液以模擬掩埋場的環境，然而，TCLP檢測方法有其限制，尤其在檢測鹼性廢棄物或材料時，儘管使用pH 2.9的醋酸溶液也可能在短時間內變為鹼性，使重金屬離子形成不溶性的氫氧化物，低估這些廢棄物或材料應用於真實環境後之金屬溶出量，其低估程度在受酸沉降影響的地區可能更為顯著。此外，也可能在環境條件的變化下，使初期TCLP檢驗合格的焚化再生粒料隨時間而變得不穩定，進而釋出更高量的有害金屬。本研究目的為以不同溶出程序，包含傳統的TCLP、多點pH溶出試驗和乙二胺四乙酸(EDTA)添加之TCLP評估焚化再生粒料及其製成的混凝土中重金屬溶出潛勢。其中多點pH溶出試驗的目的為模擬在不同最終pH值條件下，重金屬之溶出，而EDTA添加之TCLP為本研究所提出，用於模擬在含大量有機物的環境下重金屬之溶出情形。本研究以高雄兩焚化爐底渣製成之焚化再生粒料及其固化後之控制性低強度回填材料(CLSM)和低密度再生透水混凝土(MRC)進行試驗。結果顯示，經由TCLP試驗，這些材料都符合標準，且固化後更能降低重金屬之溶出。但在pH較低或含大量有機物的環境下，TCLP則會低估金屬的溶出，在多點pH溶出試驗和EDTA添加之TCLP試驗中發現，在最終pH 分別小於4.5和5或EDTA 濃度大於7 毫莫爾時，鉛及銅會超過再利用標準。此外，添加7 毫莫爾 EDTA之TCLP的金屬溶出量和最終pH值4-5的金屬溶出相當，考慮其操作流程的簡易性，本研究建議EDTA添加之TCLP可作為取代TCLP做為檢測鹼性廢棄物或材料環境相容性的方法。

關鍵字

焚化再生粒料 ； 固化 ； 毒性特性溶出試驗 ； 重金屬 ； 酸鹼值 ； 乙二胺四乙酸

並列摘要

Incinerating recycled aggregate (IRA) is produced from bottom ash, the byproduct generated from the incineration of municipal solid waste, after pre-treatments such as crushing, classifying, water washing and carbonation. In Taiwan, IRA is currently regulated under Taiwan EPA “Bottom Ash Reuse Management” and can be reused as construction materials if the toxicity characteristic leaching procedure (TCLP) results meet the reuse standards at required testing frequency. In addition, IRAs can be further stabilized using cement-based solidification/stabilization (S/S) to improve their environmental compatibility. In the TCLP test, pH 4.9 or 2.9 acetic acid which depends on the pH of samples is used as the leaching solution to simulate the release of toxic substances in landfill. However, its applicability to alkaline materials/wastes can be limited because the pH 2.9 acetic acid solution may turn into alkaline in a short time and result in the precipitation of insoluble hydroxides. This may underestimate the leaching of metals from IRAs especially if the reuse is in regions suffering from acid precipitation. Moreover, as environmental conditions change, the original IRAs qualified for reuse may become unstable as time proceeds and release unacceptable levels of heavy metals. In this study, the leaching of heavy metals from IRAs with and without solidification/stabilization (S/S) were evaluated using different leaching procedures including traditional TCLP, multi-point pH leaching test which determines metal leachability at different final pH and EDTA-mediated TCLP which determines metal leachability in the presence of high levels of organics. IRAs produced from bottom ashes collected from two incineration plants in Kaohsiung, controlled low-strength materials (CLSM) and multi-functional regenerated concrete (MRC) made of these two IRAs were employed. The results showed that the leaching of metals from these materials met the reuse standards using TCLP and that after S/S, the leaching of metals tend to decrease. However, the results obtained using multi-point pH leaching test and EDTA-mediated TCLP showed that the release of Pb and Cu could exceed the reuse standards when the final pH was < 4.5 and 5, respectively or in the presence of > 7 mM EDTA. Moreover, the amounts of metal released are comparable between multi-point pH leaching test at pH 4-5 and EDTA-mediated TCLP at 7 mM. Considering its easy procedures, EDTA-mediated TCLP is recommended as the alternative of traditional TCLP to evaluate the environmental compatibility of alkaline wastes/materials during their reuse.

並列關鍵字

Incinerating recycled aggregate (IRA) ； solidification/stabilization (S/S) ； toxicity characteristic leaching procedure (TCLP) ； heavy metals ； pH value ； EDTA

參考文獻

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