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  • 學位論文

放射性廢棄物處置之優質緩衝回填材料研製

Preparation of advanced buffer materials for application to radioactive waste repository

指導教授 : 陳建瑞 鄧希平

摘要


蒙托土(mmt)是目前放射性廢棄物處置設施中廣泛使用的緩衝回填材料,但蒙托土對銫離子的吸附選擇性欠佳,尤其在高離子強度環境,背景溶液中的陽離子會與銫離子競爭吸附,降低蒙托土對銫離子的吸附。鑒於此,本研究利用四級銨鹽(HDTMA)、18-CROWN-6(18C6)和222-cryptand等有機物質,改質鈉型蒙托土,製備優質緩衝回填材料。利用X光繞射(XRD)、電子顯微鏡(SEM)、熱重分析(TGA)和氮氣表面吸附方式(N2-BET)等技術,分析有機黏土的基本性質與特性,並進行銫離子吸附實驗,評估有機黏土的功能表現。 實驗結果顯示經由18C6改質蒙托土(18C6-mmt)在0.1 M背景離子強度下,對銫離子的吸附率最高可達94%,比原始鈉型蒙托土對銫離子的吸附率提高約5%,而在1 M背景離子強度下,對銫離子的吸附率最高可達77%,比原始鈉型蒙托土對銫離子的吸附率提高約11%;經由222-cryptand改質的有機黏土(cryp-mmt)在0.1 M背景離子強度下,對銫離子的吸附率最高可達96%,比原始鈉型蒙托土mmt對銫離子的吸附率提高約8%,而在1 M背景離子強度下,對銫離子的吸附率最高可達84%,比原始鈉型蒙托土對銫離子的吸附率提高約20%,其中crypt-mmt的吸附選擇性和吸附率又比18C6-mmt顯著,所以利用18-crown-6和222-cryptand修飾原始鈉型蒙托土,可增加對銫離子的吸附選擇性和吸附率,然而,利用四級銨鹽+18-crown-6或是四級銨鹽+222-cryptand改質的18C6-4o-mmt和crypt-4o-mmt對銫離子吸附率和吸附選擇性都較18C6-mmt和crypt-mmt欠佳,故日後製備高吸附選擇性的優質緩衝回填材料時,四級銨鹽銨鹽改質步驟並不是必要改質步驟。

並列摘要


Montmorillonite is widely used as backfilled/ buffer material in radioactive waste repository facilities. However, the shortcomings of poor sorption selectivity of montmorillonite need to be improved by surface modification. The self-assembly modification of Na-montmorillonite through the intercalation of hexadecyl- trimethylammonium (HDTMA), 18-crown-6 crown ether (18C6) and 222-cryptand (crypt) into the clay’s interlayer spaces was achieved in this study. Means including X-ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TG), and N2-BET analysis were applied to probe the surface properties of obtained self-assembly organoclays. Moreover, their performances were examined by conducting Cs sorption experiments. The XRD results demonstrated the expanded interlayer spaces of obtained self-assembly organoclays due to successfully intercalation of HDTMA, 18C6, and crypt molecules. SEM observation showed the aggregated appearance of self-assembly organoclays with reduced particle sizes. The FTIR analyses showed the reduced amount of water adsorbed on self-assembly organoclays after modification. The TG results revealed the excellent thermal stability of obtained organoclays. Organoclays modified with 18-crown-6 or 222-cryptand possess higher sorption selectivity toward cesium cation compared to raw montmorillonite samples. Particularly, over 10 % of increase in the Cs sorbed ratio under 0.1 N NaCl background solutions was achieved by the crypt-mmt and 18C6-mmt samples. These observations demonstrated the high Cs sorption selectivity of 18C6-mmt and crypt-mmt. In contrast, organoclays pretreated with HDTMA didn’t show any significant improvement in Cs uptake under high ionic strength solutions. The latter observation implied that HDTMA modification prior to 18C6 and crypt intercalation is not the necessary step when preparing high sorption selectivity buffer/back-filled materials.

並列關鍵字

montmorillonite HDTMA Cesium

參考文獻


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