有機物質對鍶核種在蒙托土吸附行為影響之研究

Effect of Organic Matters on Sr sorption to montmorillonite

王清海(Tsing-Hai Wang)

指導教授 ： 鄧希平

國立清華大學/原子科學院/核子工程與科學研究所/博士(2010年)

https://doi.org/10.6843/NTHU.2010.00042

摘要

本研究利用在自然界中發現的有機小分子作為天然有機分子類比物，探討有機分子對鍶離子(Sr2+)於蒙托土表面吸附行為的影響。並利用MINEQL+模式擬合實驗結果，推論出反應環境的平衡常數logK，藉由觀察logK的改變，討論有機物質存在對鍶離子(Sr2+)吸附行為的影響。
由MINEQL+模式解析鍶離子(Sr2+)吸附特徵發現，背景陽離子與鍶離子競爭蒙托土平面吸附位置，導致logKx從4.0(I = 0.017 M)降低至2.2(I = 0.1 M)，但邊緣吸附位置對鍶離子(Sr2+)的吸附增加，使logKs從-0.3(I = 0.017 M)增加至8.5(I = 0.1 M)，表示蒙托土的邊緣吸附位置對鍶離子(Sr2+)有較高的吸附親和力。此外，在相同背景濃度時(I = 0.017 M)，當起始鍶離子(Sr2+)濃度從100 ppm降低至10 ppm，logKs從-0.3升高至1.3，顯示在低鍶離子(Sr2+)濃度時，蒙托土的邊緣吸附位置對鍶離子(Sr2+)吸附的重要性增加。
由巨觀的鍶離子(Sr2+)吸附變化量發現，有機分子對鍶離子(Sr2+)的吸附行為並沒有顯著影響。MINEQL+模式解析發現，有機分子的存在競爭了蒙托土的邊緣吸附位置，導致logKs從-0.3降低至-1.3(羧基類) ~ -2.3(苯環類)。表示在中性與鹼性環境下，有機分子會降低蒙托土對鍶離子(Sr2+)的吸附量。同時，有機分子的存在會產生大量的懸浮固體。
比較純有機環境和鍶離子(Sr2+)與有機分子共存環境的有機濃度變化，發現鍶離子(Sr2+)存在會增加有機分子的吸附。這表示鍶離子(Sr2+)是有機分子吸附在蒙托土表面的吸附橋梁。並藉由此現象，有機分子被鍶離子(Sr2+)帶入蒙托土的層間，改變層間水的分布狀況。
由XRD圖譜發現，有機分子與鍶離子(Sr2+)共同存在時，蒙托土層間水分子組成會有不同的影響。在酸性環境下，層間水分子組成沒有明顯的改變。但在中性環境下，雙層水分子組成的層間排列比例會增加。在鹼性環境下，有機分子的存在增加雙層水分子組成的層間。表示鍶離子(Sr2+)將有機分子帶入蒙托土的層間。而FTIR分析結果顯示，有機分子是透過外圈錯合機制吸附於蒙托土表面。

關鍵字

蒙托土 ； 鍶 ； 吸附 ； 結構位置 ； 邊緣位置 ； MINEQL+

並列摘要

The influence of natural organic matters (NOMs) on strontium (Sr2+) sorption to montmorillonite was investigated in this study by using some defined structure low-weight organic species as NOMs sarrogates. With assistance of MINEQL+ code, results from Sr2+ sorption were quantified to reaction equilibrium constats (logK).
It was found that stronger background electrolytes competed with Sr2+ for the structure sorption sites, and caused a decrease in logKx from 4.0 (I = 0.017 M) to 2.2 (I = 0.1 M). However, the logKs rose from -0.3 (I = 0.017 M) to 8.5 (I = 0.1 M), indicating a higher sorption affinity of the edge sorption sites toward Sr2+. Under identical background strength (I = 0.017 M) environments, when Sr2+ concentration droped from 100 ppm to 10 ppm, the corresponding logKs rose from -0.3 to 1.3. This demonstrated the important role of the edge sorptioin sites under low Sr2+ environments.
By comparing Sr2+ sorption ratios obtained under varios concentrations of organic species, it was found that Sr sorption was unaffected by the presence of organic species. However, results from MINEQL+ code showed that aqueous organic species competed for the edge sorption sites against Sr2+, and reduced the values logKs from -0.3 to -1.3 (COO group) or to -2.3 (aromatic group). This indicated that the presence of organic species would reduce Sr2+ uptake under neutral and alkaline environments. Moreover, organic speices also increased the concentration of suspension solids.
It was found that organic species uptake was greatly increased with the presence of Sr2+, indicating sorbed Sr2+ acts as sorption bridges for organic species. That is to say, organic species were introduced into interlayer of montmorillonite along with Sr2+. Intercalated organic species rearranged the distribution of interlayer water molecules, resulting in the various compositions of interlayer environments as indicated by XRD observations. Furthermore, FTIR results confirmed that organic species were sorbed to montmorillonite through outer-sphere complexation.

並列關鍵字

Montmorillonite ； strontium ； sorption ； structure sites ； edge sites ； MINEQL+

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