有機銨鹽改質膨潤土其銫離子吸附行為之研究

Adsorption behavior of Cesium ion affected by alkylammonium salts modified organoclays

謝其融(Chi-Jung Hsieh)

指導教授 ： 陳建瑞 ； 鄧希平

國立清華大學/工學院/材料科學工程學系/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00387

摘要

核能的運用伴隨而來的是放射性廢棄物的產生，處置場的建構是為必要。在回填作業上所選用之工程障壁材料〝膨潤土〞，已被許多處置經驗各國所選用，因為其對核種陽離子具良好的吸收特性，以及高膨脹特性能有效阻止水流穿透。而在放射性廢棄物中有可能造成遷移核種中，以銫核種半衰期30年為最長，對生物圈影響最深遠，需要嚴加控管。若未來需執行監控，將需要更多的膨潤土吸附銫離子相關研究報告。
本研究中為探討有機銨鹽物質對膨潤土吸附銫離子行為所造成的影響 ，以一倍CEC濃度的有機銨鹽作為黏土改質物形成有機改質黏土，由此觀點進行銫離子的吸附實驗。首先利用XRD 、FTIR 、BET 作為對改質後黏土結構與表面特性認定，而電位滴定實驗更可建立後續模擬實驗所需參數，另一方面進行銫離子吸附實驗，可由吸附實驗結果初步了解其不同改質物質對銫離子吸附行為的表現，結果指出鈉離子飽和處理黏土(Na-MX80)相較於原始未受處理前MX80，具有較佳的吸附表現，尤其是愈酸性環境其差異越多；改質黏土部分顯示，一級銨鹽改質黏土較四級銨鹽有較好的吸附效果，特別的是碳鏈長度為16之銨鹽類，皆表現出比原始MX80 差的吸附效果。
最後結合先前所建立參數與吸附實驗結果，以MINEQL+程式搭配雙層吸附模型，模擬銫離子在黏土表面吸附行為，藉觀察不同吸附位置其表面解離常數的變化，進而討論對吸附行為的影響。比較模擬結果發現，一級銨鹽改質黏土其邊緣吸附位置(edge adsorption site)貢獻會隨長碳鏈之碳數增加而提升，而結構性電荷位置貢獻反之下降，於碳數為16處為最低點；四級銨鹽改質黏土其邊緣吸附位置貢獻稍微下降，隨碳數增加影響並不顯著，而其結構性電荷位置則維持較低的貢獻，但於碳數為12處有顯著增加。此外，懸浮固體量測實驗指出，四級銨鹽改質黏土在減少懸浮固體的效果上較一級銨鹽改質黏土佳。

關鍵字

膨潤土 ； 有機銨鹽 ； 銫 ； 吸附 ； 懸浮固體

並列摘要

The use of nuclear energy is accompanied by the generation of radioactive waste, so the construction of radioactive disposal repository is necessary. In the backfilling process, the principal component of engineering barrier material is〝Bentonite〞. Because of it’s excellent sorption capabilities for cationic radionuclides and high-swelling property against the water to penetrate through the clay, it has been widely used in many countries. Among the nuclides of radioactive wastes that might migrate to living environment, Cesium ( Cs ) has the longest half-life for about 30 years. It may cause the most far-reaching effect on the biosphere. The migration of Cs+ should be supervised and controlled strictly. To evaluate and supervise the radioactive disposal sites in the near future, it will require more reports on this kind of research.
In this study, in order to investigate the effect of alkylammonium salt of organic substances to the Cs+ adsorptive behavior, the adsorption experiments were performed with MX-80 clay treated with primary/ quaternary alkylammonium salt in amounts equivalent to cation exchange capacity (CEC). Firstly, the analytical methods of XRD、FTIR and BET were used for determining the structure and the surface properties of the clay, and the potentiometric titration experiment can establish the necessary parameters for the subsequent simulation. From the result of the adsorption experiment, the preliminary understanding of the Cesium ion adsorption behavior is obtained. This result pointed out that Na-MX80 had better Cs+ adsorption behavior than that of untreated MX80, especially in the acidic environment. Secondly, on the part of the modified clay, the clay modified by the primary alkylammonium salts had better adsorption effect than that by the quaternary alkylammonium salts. Particularly, the modified clays with number 16 carbon chain length of the ammonium salt showed poor adsorption result than that of the untreated MX80.
Finally, the parameters established from the previous experiment results were linked up with MINEQL+ program and combined with double-layer model to simulate the adsorption of cesium ions on the clay surface. By observing the surface adsorption dissociation constants of different adsorption sites, we can discuss the adsorption behavior further.
According to the results of modeling, the contribution of edge adsorption sites of the clays modified by the primary alkylammonium salts would increase with the carbon number of carbon chain, while the contribution of structural adsorption site decreased with the carbon number, especially decreasing most in 16-C; the contribution of edge adsorption sites of clays modified by quaternary alkylammonium salts slightly decreased with the carbon number of carbon chain. However, the contribution of structural sites remained in a low level, while there is a remarkable increase in 12-C.
Furthermore, the measuring experiment of solid suspension( S.S.) exhibited that quaternary alkylammonium salts modified clay showed better effect than primary alkylammonium salts modified clay on reducing the solid suspension.

並列關鍵字

bentonite ； alkylammonium salts ； Cesium ； adsorption ； suspension solid

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