| 摘要: | 本研究採用Thermite反應放熱將焚化飛灰予以高溫熔融處理，分析熔融前後各組成元素與重金屬之移轉與溶出行為，印證產物無害化。並進一步探討熔渣工程性質，以提供熔渣未來資源化可能方向。 研究結果顯示，熔融溫度變化範圍在1744-2781℃，決定於鋁熱劑與飛灰之質量比率，飛灰對混合物質量比率每增加1%，反應溫度以線性約下降172℃。最大處理比例為飛灰對應起始混合物30%。 起始反應物各主要組成元素及重金屬之分佈依各元素及重金屬之熔沸點及蒸氣壓特性而變。重金屬Cd主要分佈於氣相中；Pb、Zn分佈於熔融飛灰中。Cu、Cr、Ni及Fe主要分佈於熔渣與金屬錠中，熔融溫度越高，金屬錠中之比率隨之增高。Ca、Si則主要分佈於熔渣相中。Al隨熔融反應溫度升高，主要分佈由熔渣中隨之轉移分佈於熔融飛灰中。熔渣對起始混合物質量百分比與飛灰摻量對起始混合物質量百分比成線性上升關係，金屬錠對起始混合物質量百分比與飛灰摻量對起始混合物質量百分比成線性下降關係。依化學反應配置之鋁熱劑（AF）與使用一半鎂粉取代鋁粉作為還原劑之鋁熱劑（AMF之鋁熱劑）熔融時物種轉移行為相似，但在鋁熱反應中加入的過量鋁粉（A2F鋁熱劑）會與飛灰中物種發生作用，使其還原為元素態。此行為將使Pb不易揮發，Cd與Zn更易揮發。 金屬錠含鐵量大多達97%以上。熔渣呈玻璃化結構，重金屬溶出已低於法規標準且具長期穩定性；其體比重多在2以下，視孔隙率在2-25 %間，吸水率在1.55-16 %間；線膨脹率多低於15%，對酸鹼抵抗力多在80%以上。由此顯示Thermite法熔融處理後之熔渣與金屬錠皆具備高度資源化與材料化之發展潛力。 This study investigated the feasibility of melting fly ash for a recycling purpose, by using chemical energy released by the reaction of waste-derived thermite. Typical thermite tested in this study comprised of strong-exothermic aluminum and iron(Ⅲ) oxide, simulating aluminum dross from aluminum foundries and iron oxides from the fly ash and byproducts of steelworks in industrial practice. The self-propagating characteristics of the targeted thermite treating municipal solid wastes incinerator(MSWI) fly ash was evaluated by varying fly ash content in the starting mixture (thermite mixed with fly ash) from 5% to 35% by weight. The distribution of major elements (Al, Fe, Ca, and Si), and the partitioning of heavy metals during thermite type melting process were determined. The recovered alloy and slag were analyzed for their composition and engineering properties. The results indicate that the self-propagating temperature required a maximum fly ash content less than 30%, corresponding to a melting temperature higher than 2017K in this study. The maximum reaction temperature reached was found to be 3055K for thermite without addition of fly ash, depending on the fraction of heat loss from the thermite reactor. It was also noted that the recovery of slag increased with increasing MSWI fly ash content in the starting mixture whereas greater than 91% alloy, mainly iron, was recovered. The major elements in thermite and MSWI fly ash, including Al, Fe, Ca, Si, were evaluated. It was found expectedly that most of the iron was recovered in alloy, and aluminum in slag and secondary fly ash (generated from melting process, SFA). The distribution of Al to SFA decreased with increasing ash addition, showing the violent character of the thermite reaction was weakened. Calcium and silicon existed in MSWI fly ash as calcium oxides and silicon oxide, and were mostly recovered in slag. In the thermite reactions with half of the Al replaced by Mg, and with 100% excess of stoichiometric Al, it was found that the volatility of Pb was decreased; whereas the volatility of Cd and Zn was enhanced. Moreover, the recovered slag showed stable vitrified structure with extremely low TCLP leaching concentration of heavy metals which complies with current regulatory thresholds. The slag has a specific gravity less than 2, with apparent porosity ranging from 2-25%, and water adsorption from 1.6-16%. Most of the slag samples has a linear expansion less than 15%. The ability of anti-acid(base) corrosion for all slag samples is greater than 80%. This study demonstrated that a thermite reaction of aluminum and iron oxide treating MSWI fly ash was demonstrated to be a feasible approach to recover metallic resources and slag for construction materials. |
