磷酸活化對蒙脫土表面吸附性的改質研究

Effect of phosphoric acid activation on montmorillonite surface : a sorption property study

劉宗穎(Tsung-Ying Liu)

指導教授 ： 陳建瑞

國立清華大學/工學院/材料科學工程學系/碩士(2008年)

摘要

本研究利用不同的磷酸濃度和三種處理時間(3、12和24小時)來活化蒙脫土以製備緩衝回填材料，並以銫離子等溫吸附實驗評估活化蒙脫土對銫離子吸附量的表現。根據實驗結果顯示：活化蒙脫土在吸附過程中的產生的懸浮固體量低，所以由磷酸活化的蒙脫土的材料穩定性佳，足以運用於緩衝回填材料；且根據Langmuir model結果，活化蒙脫土的吸附量遠大於蒙脫土，這是由於蒙脫土在活化的過程中增加比表面積，由FTIR、BET比表面積可以證明蒙脫土結構裂解而增加比表面積，而且裂解的程度隨活化時間增加而提高。
同時，活化蒙脫土在高濃度的鉀和銨離子溶液中展現相當良好的吸附選擇性，這是因為蒙脫土在活化時表面質子化，進而造成表面電荷密度提高，並可以由pH值滴定和陽離子交換容量分析得到證實。其中又以活化三小時的蒙脫土表面電荷密度最高，所以有最好的吸附選擇性。
綜合所有實驗結果，活化三小時蒙脫土擁有高吸附性和選擇性，所以具備優質緩衝回填材料的條件，將可以降低外洩放射性廢料對人類生活環境圈的影響。

關鍵字

蒙脫土 ； 緩衝回填材料 ； 活化 ； 吸附 ； 銫離子

並列摘要

In this study, phosphoric acid with different concentrations and activation times is used to active montmorillonite (mmt) powder to prepare a promising backfill and buffer material for radioactive waste repository. At the same time their performance are evaluated by cesium sorption experiments. The experimental results show that the amount of suspension solids in these sorption experiments is not significant, which stands for the stability of these phosphoric acid activated montmorillonite (PAmmt). According to the fitting results by Langmuir model, PAmmts behave a much higher sorption capacity toward Cs ions than the original mmt. The high sorption capacity is strongly related to the increased specific surface area, which is confirmed by the N2-BET method. Further XRD and FTIR analyses demonstrate that the mmt structure is deconstructed during the activation, at which the degree of deconstruction depends on the concentration of phosphoric acid and reaction time. Also these PAmmts show a high selectivity even in high saline potassium or ammonium solutions. This is attributed to the higher surface charge density produced by surface protonation, which is supported by experiments of potentiometric titration and cation exchange capacity. Based upon experimental results, three hours of phosphoric acid activation is suggested to prepare a high selectivity along with a good sorption capacity for use in the radioactive waste repository.

並列關鍵字

Montmorillonite ； Backfill and buffer material ； Acid activation ； Sorption ； Cesium

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