具分散反萃取相支撐式液膜穩定性之評估

Abstract

具分散反萃取相之支撐式液膜（ Supported Liquid Membrane with Strip Distribution）相較於傳統之支撐式液膜，其有機相不易流失，因此穩定性較佳，此外，也具備了操作簡便、反萃取效率高及可高度濃縮待萃物質……等優點。因此，本研究選用具分散反萃取相之支撐式液膜，利用中空纖維模組（hollow fiber module）來回收工業廢液中之銦離子並加以濃縮，以獲得銦之二次資源。在操作過程中，我們觀察到液膜會有不穩定現象，如第三相（第二種有機相）生成所造成的膜結垢現象。本研究將針對此不穩定現象進行評估，並尋求改進，期能使此液膜回收程序更具實用性。 本研究利用具分散反萃取相之支撐式液膜處理含高濃度（約5,000~10,000 ppm）銦離子之進料溶液。我們選用0.6 M 之酸性萃取劑-二(2-乙基己基)磷酸（D2EHPA）及2 vol%之修飾劑十二醇（dodecanol）溶於稀釋劑isopar-L 中作為有機相，並以5 M HCl 為反萃取溶液。在操作過程中，發現銦離子與萃取劑所形成之錯合物會因有機相中銦濃度達飽和而沈澱析出，造成支撐膜結垢及處理效率下降。此沈澱物為第二種有機相，因此又稱為第三相，生成的原因可能是D2EHPA萃取銦離子之速率大於In-D2EHPA 錯合物於支撐膜孔內之擴散速率，而造成錯合物累積於支撐膜內。故我們嘗試降低萃取劑的用量使萃取速率降低，並增加修飾劑dodecanol 的比例以提高錯合物的溶解度，以抑制第三相的生成。實驗結果顯示，當有機相含0.05 M D2EHPA 及10 vol% dodecanol 時，支撐膜的結垢現象有大幅的改善。

Compared to the traditional supported liquid membrane process, the supported liquid membrane with strip distribution（SLMSD）has less loss of organic phase during operation and also the advantages of easy operation, high stripping rate, and high concentration ratio of target species. In the present research, indium ion was recovered from industrial wastewater by the process of SLMSD with hollow fiber modules, to get the second resource of indium. During the process of recovery, we observed instability of supported liquid membrane, such as the water transfer caused by the osmotic pressure differences across the membrane and the membrane fouling caused by the third-phase formation. These phenomena affected the efficiency and stability of the recovery process. The main purpose of this research is to evaluate the stability of SLMSD, and to find ways to improve the stability, so as to make this process more practical in industry. In this research, we recovered indium ion from the feed solution with higher indium concentration (about 5,000~10,000 ppm) by SLMSD. The organic phase contained D2EHPA as extractants, dodecanol as modifiers and isopar-L as diluents, and the strip solution was 5 M HCl aqueous solution. During the operation, we found that the concentration of In-D2EHPA complexes saturated in the organic solution and then deposited on the membrane to cause the membrane fouled and the recovery efficiency decreased. The deposits were the second organic phase, so they were also called the third phase. Because the extraction rate of indium from the feed solution was larger than the diffusion rate of In-D2EHPA complex in the organic phase, so the In-D2EHPA complexes accumulated and finally saturated in the organic phase inside the membrane pores. So we decreased the concentration of D2EHPA to lower the indium extraction rate, at the same time, we increased the concentration of dodecanol to raise the complex solubility in the organic phase. As the experimental result showed, when the organic phase contained 0.05 M D2EHPA and 10 vol% dodecanol in isopar-L, the condition of membrane fouling was inhibited a lot.