機械化學處理焚化飛灰對鉛穩定機制及製備陶瓷材料之研究

The study on the Mechanism of Pb(II) stabilization and the preparation of ceramic materials with MSWI fly ash by mechanochemical treatment

吳靜薇(Ching-Wei Wu)

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(2013年)

https://doi.org/10.6846/TKU.2013.00649

摘要

台灣地區的垃圾係以焚化為主要的處理方式，焚化處理雖具有減容、減量、衛生之效果，但仍產生一定比例的灰渣，其中飛灰內含重金屬等有害物質，易溶出而超過有害廢棄物認定標準，因此被判定為有害廢棄物，需經適當處理降低其毒性後始可進掩埋場。由於新掩埋場開發愈形不易，且固化體的長期重金屬穩定性仍有疑慮，因此追求有效的飛灰無害化及資源化技術之開發，已成為刻不容緩的議題。
本研究引進機械化學反應(Mechanochemical Reaction)之觀念，藉由機械能促使飛灰中的重金屬特性改變，達到穩定不易溶出的效果。本研究以採高能球磨以減少所需的研磨時間，首先找出最佳的濕式高能球磨操作條件，再探討重金屬鉛穩定機制。此外，機械化學研磨後由於粒徑減小，大幅度提高表面積，有助於吸濕性能，故嘗試再利用為製備調濕陶瓷材料的原料，搭配含大量鋁矽酸鹽的高嶺土，提高燒結性。另一方面，利用飛灰富含鈣基的特性，與高嶺土進行調配，並藉由機械研磨達成軟化學合成反應，製成鈣長石基陶瓷產品。
由實驗結果發現，濕式高能球磨研磨8小時即可達到傳統濕式球磨研磨96小時對鉛的穩定效率。而鉛在飛灰之高pH值下與氯離子反應生成Pb7O6Cl2的沉澱，經研磨處理後會形成較穩定的PbO2及Pb2O3。由數學關係式求得鉛穩定因子權重，發現研磨灰穩定能力最高，達92.44 %，鉛氯鹽沉澱穩定效果最低且為負值，且在試驗中會影響其他作用的穩定性。
機械化學研磨8小時的水萃飛灰與高嶺土調配後可製成良好調濕性能的調濕陶瓷材料，吸濕量為日本調濕建材性能評價委員會之等級3，放濕率並可達到70 %標準。而研究中也發現鈣鋁石(Mayenite，Ca12Al14O33【C12A7】)之繞射峰強度與吸放濕量成正比，而鈣鋁黃長石(Gehlenite，Ca2Al2SiO7【C2AS】)之繞射峰強度則成反比，鈣鋁石的生成有助於長時間研磨的燒結體之吸放濕。
機械研磨飛灰-高嶺土不僅將粉體粒徑減小，且使粉體達到無晶序化(amorphization)，粉體的無晶序化和燒結後鈣長石相對含量具正相關；而以焚化飛灰作為合成鈣長石的鈣源，經研磨粉體燒製後，可觀察到眾多短柱狀的鈣長石結晶，成功製備出鈣長石基陶瓷材料，並將燒製的溫度從1,300 ℃降至950 ℃，經燒製後的產品，重金屬溶出已經非常低，產品已無害化。

關鍵字

焚化飛灰 ； 機械化學 ； 鈣長石 ； 無晶序化 ； 鉛穩定 ； 調濕陶瓷

並列摘要

In Taiwan, incineration had become the major method to treat the municipal solid waste. Incineration has the advantages of good volume and mess reduction efficiency and healthy, but the residual fly ash was classified as hazardous waste since it contained much heavy metals, which could not pass the TCLP test, and should be solidified before landfilling. Nevertheless, the landfill site is difficult to be installed, and the long-term stability of the heavy metals of the solidified matrix was doubted by the publics. Therefore, to develop new detoxification and recovery technologies for fly ash are urgently.
This study introduced the concept of mechanochemical reactions, which provided mechanical energy to promote the characteristics change of the heavy metals in the fly ash to reach the aim of stability. In this study, the high energy ball milling was used to reduce the milling time. The optimum operation conditions for wet milling were studied, and then to explore the stabilization mechanism of lead. Furthermore, milled fly ash powder was blended with aluminum silicate rich kaolin, and sintered to produce humidity-controlling ceramic as the ecological building material. On the other hand, the soft mechanochemical synthesis mechanism was applied in the anorthite-based ceramic production with fly ash blended with kaolin, due to the rich calcium-based property of fly ash.
The results showed that, 8 hours milling can reach the effect of 96 hours traditional wet ball milling for lead stabilization. Lead in the high pH could react with chloride ions to generate Pb7O6Cl2 precipitation, after milling, the much stable species PbO2 and Pb2O3 will produced. The results of the mathematical relationship analysis for weight factors of lead stabilization showed that, the highest weight factors is milled ash, 92.44 %; but the lowest is lead chloride salt which weight factor, which is negative, and it will affect the other stability effects.
The humidity-controlling ceramic produced from mixed powder milled 8 hours and then sintered at 1,000 oC performed 70 % moisture absorption ability, which can meet the grade 3 standard in Japan. It was found that the intensity of the diffraction peaks of mayenite (Ca12Al14O33, C12A7) of sintered sample is proportional to the amount of moisture absorption and desorption, while calcium aluminum (Ca2Al2SiO7, C2AS) is inversely proportional. Therefore, the mayenite generated in sintered specimen is helpful to moisture absorption and desorption.
Mechanical milling of the fly ash with kaolin not only decreases particle size, but also transforms the crystals into amorphization. Furthermore, the amorphization of the powder and relative content of anorthite after sintering process have a positive correlation. Using fly ash as a calcium source to synthesize anorthite by milling and sintering could observe many short columnar crystals of anorthite. The process of milling and sintering can successfully prepare anorthite-based ceramic materials and could decrease the sintering temperature from 1,300 oC to 950 oC. The leaching of heavy metals of the product is very low and it has been harmlessly.

並列關鍵字

MSWI fly ash ； mechanochemistry ； anorthite ； amorphization ； Pb(II) stabilization ； humidity-controlling material

參考文獻

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