以流電極電容去離子技術濃縮碘化鉀

Abstract

隨著經濟發展，碘已成為化學合成工業、製藥產業與面板製程等方面不可或缺的元素，然而近年來碘的生產與銷售逐漸被單一國家所壟斷，且受限於環保法規，含碘廢水須妥善處理，故深具回收價值。考量碘回收時的能耗問題，本論文提出以流電極電容去離子技術回收低濃度含碘廢水，並加以濃縮。 首先以批次式進料結合接續再生系統測試各操作參數下性能表現，綜合評估移除速率、再生速率、電流效率、能耗及陰離子交換膜沉積情形等結果，選擇回收操作條件為:以0.4 V與-0.4 V作為離子移除與回收的操作電壓，且不調整酸鹼值，此條件雖然速率最慢，但電流效率較高、且能耗較低。操作過程中雖然無法避免I-氧化生成I2，但I2可與I-結合成I3-，仍能順利從活性碳上脫附並透過離子交換膜順利將碘回收。 本研究第二部分則是以上述操作條件進行碘化鉀移除同時進行流電極再生，以批次式進料進行測試，觀察到進料中的碘、鉀離子幾乎可被完全移除，也可順利從流電極中被回收濃縮。另外亦觀察到在低濃度進料時，離子移除速率會與濃度一次方成正比，而當進料濃度提高時，移除速率則會趨近於一定值，離子移除速率與進料濃度間的關係可以 \frac{\mathrm{1}}{\mathrm{r}}\mathrm{\ =\ A\ +\ }\frac{\mathrm{B} }{\mathrm{C}} 描述，從實驗數據可以迴歸出A、B的數值，發現B為一常數，而A會因為碘沉積在上而變大，使速率降低。 本研究第三部分，則是在同時進行離子移除和流電極再生的操作下，對連續進料進行KI回收。結果顯示: 1.00 mM與2.50 mM的碘化鉀水溶液以18 ml/min之流速連續流入系統，20小時後可得到碘濃度70.90 mM (9010 ppm)與152.00 mM (19290 ppm) 100 ml的濃縮液，濃縮倍率分別為58.5、60.8倍。我們也以第二部分所推出的離子移除速率式來計算連續操作時的離子移除和回收速率，計算結果與實驗數據相當吻合，顯示所用的速率-濃度關係式可以做為系統放大的設計依據。

Iodine has been the indispensable element in chemical synthesis, pharmaceutical, and panel manufacturing process due to economic development. However, the produce and sales of iodine have been monopolized by single country. Besides, proper treatment of iodine-containing wastewater is needed to be done because of the environmental regulations. Therefore, it is worthwhile to recovery iodine. In this thesis, we propose recovering and concentrating the low concentration iodine-containing wastewater by flow-electrode capacitive deionization under the consideration of energy consumption. We first test the performance of a batch-mode deionization with successive regeneration system in various operating parameters. After a comprehensive evaluation of removal rate, regenerated rate, charge efficiency, energy consumption and the iodine deposition in anion exchange membrane, we choose the operating parameters: 0.4 V of charge voltage and -0.4 V of discharge voltage without pH controlling which lead to the lowest rate but highest charge efficiency, lowest energy consumption. Although it is unavoidable to generate I2 from the oxidation of I- during operation, both could combine with each other to form I3- and be recoveried through ion exchange membrane after desorption from activated carbon. The second part of the study is about the performance of a batch-mode deionization with simultaneous regeneration system by the operation parameters mentioned above. We found that almost all iodide and potassium ions in feed solution could be removed and successfully recoveried and concentrated from flow electrodes. Also, a proportional relationship between concentration and removal rate was observed under low feed solution concentration while the removal rate approaches to constant at high concentration. The relationship between ion removal rate and feed concentration could be described as \frac{\mathrm{1}}{\mathrm{r}}\mathrm{\ =\ A\ +\ }\frac{\mathrm{B} }{\mathrm{C}} . The values of A and B are obtained from the regression analysis of experimental data. We found that B is a constant, whereas A would increase due to iodine deposition which reduces the rate. In the third part of this study, the continuous-mode deionization combined with the simultaneous regeneration system was carried out to recovery potassium iodide. It shows that the 100 ml concentrated solution at concentration of 70.90 mM I (9010 ppm I) and 152.00 mM I (19290 ppm I) could be obtained by treating 1.00 mM and 2.50 mM potassium iodide aqueous solution at the flow rate of 18 ml/min for 20 hours. The concentrated ratios are 58.5 and 60.8 times respectively. We also calculated the ion removal and recovery rate by the rate equation derived in second part. The results quite fit the experimental data which shows the rate-concentration equation could be the basis of scale-up designing of the system.