以疏水性中空纖維模組為油水分離器之萃取－反萃取系統開發

Abstract

液液萃取 (Liquid-liquid extraction) 為一常用之金屬離子回收方式。藉由對待萃金屬有選擇性且親和性強的有機萃取劑，將金屬離子自水相溶液中萃取至有機相溶液中。液液萃取會因為達到熱力學平衡而需要多級萃取單元操作來得到較高的移除率，或將有機相進行反萃取以破壞平衡。本研究探討如何改進液液萃取之系統，使有機相溶液能有效再生。實驗所使用之進料溶液為模擬 ITO 蝕刻廢液，其中銦離子濃度約為 200 ppm，螯合劑草酸的濃度為 2 wt%，並以此比較不同系統間之萃取速率與探討不同條件下以疏水性中空纖維模組為油水分離器之萃取－反萃取系統之金屬離子移除速率。 研究中使用多項液液萃取系統，探討不同系統移除草酸銦離子溶液中之銦離子之速率。首先分別操作批次萃取與具分散反萃取相支撐式液膜 (supported liquid membrane with strip dispersion, SLMSD) 程序，研究顯示在批次萃取情況下，因萃取面積較 SLMSD 所使用之萃取面積大而初始移除速率較快，但因熱力學平衡而無法將移除至較低濃度，而 SLMSD 技術因同時進行萃取與有機相的再生，可將金屬離子以穩定速率移除。為結合有機相再生與較大的萃取面積，第二部分改以疏水性中空纖維模組為油水分離器之萃取－反萃取系統 (extraction-stripping with hydrophobic membrane separators, ESMS) 進行實驗，將 SLMSD 中的萃取端改為批次萃取型式，並將中空纖維模組從原先的萃取接觸面積角色改為油水分離膜，利用球閥控制壓力差使有機相溶液在萃取端與反萃取端進行震盪流動，達到增加反應面積與有機相再生的目的。此系統可有效結合批式萃取較大的反應面積並結合有機相的再生，但有機相的再生速率不足仍為萃取反應之速率決定步驟。第三部分則將ESMS系統加裝另一中空纖維模組，使萃取端與反萃取端中的有機相溶液進行循環式流動，以增加有機相再生效率，並比較不同濃度之進料與不同有機相體積流速對移除速率之影響。實驗結果顯示無論在銦離子進料濃度為 1600、200、10 ppm下，均需要將有機相再生以破壞其熱力學平衡使銦離子濃度持續降低。本研究亦提出一模型，藉此解釋有機相體積流速對萃取速率之影響。 本研究也對實務上之銅廢水進行測試，分別以SLMSD及循環式ESMS操作回收廢水中之銅離子，結果顯示以 ESMS 系統具有較高的移除速率，亦具有應用於工業上的潛力。

Liquid-liquid extraction is a widely used method in metal ion recovery. By using extractant with high selectivity and affinity to the metal ion, we can extract the metal ion from aqueous solution to organic phase. However, due to chemical equilibrium, regeneration of extractant or multi-stage extraction process is needed to obtain high removal. The main purpose of this research is how to improve the regeneration of extractant in liquid-liquid extraction system. We present different solvent extraction techniques to recover indium from oxalic acid solution, which demonstrate wastewater in liquid-crystal display (LCD) process. First, we compared solvent extraction and supported liquid membrane with strip dispersion (SLMSD) process. Because of the presence of oxalic acid, indium could not be recovered completely by solvent extraction. Extraction and stripping happens simultaneously in SLMSD system, although the removal rate is slower than solvent extraction, it might recover completely if operated with longer time. To combine large surface area and extraction-stripping simultaneously, we develop extraction-stripping with hydrophobic membrane separators (ESMS) technique. Extraction and stripping is operated separately in the extraction and stripping tanks by dispersing aqueous solution (feed or strip) in organic solution, and make the hydrophobic membrane as a role of oil-water separator. We can control pressure difference in the system to force the organic phase to oscillate through membrane pores. ESMS system can combine the advantage of solvent extraction of its large reaction area and SLMSD of its organic phase regeneration. We then find oud that adding one more hydrophobic membrane into the ESMS process, and change the organic phase translation from oscillation into circulation might improve the system efficiency. We operate the system with 10, 200 and 1600 ppm indium solution with oxalic acid, and with different organic volumetric rate. Among all concentration, without the presence of stripping, the removal rate would gradually decrease due to chemical equilibrium. With the presence of stripping, higher organic volumetric rate brings to higher removal rate. We also make a model to explain how the organic volumetric rate affects the removal rate. In addition to lab research, we also dealt with copper-containing wastewater from industry to recover copper ions by SLMSD and ESMS. Experiment results show that by ESMS, we can recover copper ions with higher efficiency. Therefore, ESMS technique has its potential in industry.