以具分散反萃取相支撐式液膜分離回收稀土金屬離子

Abstract

稀土金屬具有特殊的的磁性、發光特性及電化學性質等，不僅能提升產品的效能，更能達成減重、減碳、節能等環保目的，廣泛應用於磁鐵、螢光粉與觸媒等產品中。然而稀土最大宗出產國中國自2009年限制出口配額而造成高純度的稀土金屬供給危機，近年來稀土金屬已成為各國傾力回收的戰略資源，因此如何在國內建立有效的稀土金屬分離回收技術為一重要課題。本研究使用具分散反萃取相支撐式液膜的技術，建立傳輸模型預測雙成分系統中銪、釔離子以酸性萃取劑二(2-乙基己基)磷酸（D2EHPA）萃取透過液膜的效率，並以高濃度硝酸作反萃取劑對其做分離與回收。 首先對萃取機制作探討，利用搖瓶式萃取實驗建立銪、釔金屬離子在系統中的萃取平衡式與平衡常數；第二部分利用在液膜中影響透過係數的參數- 進料相pH值、進料相流速、萃取劑濃度，調控實驗條件並以最小方插法與斜率分析法得到在進料相傳輸阻力與膜相傳輸阻力大小，結合第一部分所找到的反應平衡常數建立傳輸模型。最後利用傳輸模型設計銪、釔離子的分離實驗，在第一步驟中將進料相混和溶液中的釔離子單獨地透過液膜，透過係數為9.55×10-6 m/min，兩小時內回收率達99.7%，濃縮效果從270 mg/L至1346 mg/L。在第二步驟，調整實驗參數可將進料相中剩餘的銪離子於90分鐘內透過液膜，透過係數達4.58×10-4 m/min，回收率達99.2%，濃縮效果從28.9 mg/L濃縮至143 mg/L。經由此二階段的程序，可成功將銪釔兩離子加以分離並且得到五倍濃縮液，由結果可知此傳輸模型對單成分與雙成分系統提供了高準確度的預測，並突破以往萃取劑過量的假設，在考量萃取劑改變量的同時能夠預測高濃度稀土金屬離子溶液的透過係數，達成高處理量、高選擇性、高效率且高穩定性等目的，為日後製程放大的依據。

Rare-earth metals have a wide range of applications like phosphors, permanent magnets, catalysts, and other advanced industrial devices due to their excellent performances even in trace amount. With the increasing demand for high purity of rare-earth metals and with the supply risk caused by China, the separation and recovery of a single rare-earth metal from minerals and industrial waste have gained much attention. The present work reports on the technique of supported liquid membranes with strip dispersion (SLMSD) to separate and recover two critical rare-earth metal ions, europium (III) and yttrium (III), with organic extractant di-(2-ethylhexyl)phosphoric acid (D2EHPA) in nitrate medium. First, the dominant reactions for single rare-earth metal ion in the solvent extraction were investigated by shaking-flask experiments to obtain accurate equilibrium constants. With the equilibrium constants, transport models describing the transport and reaction of single ion in SLMSD were developed with the factors, including extractant concentration, pH value in feed, and velocity of feed. The data calculated by the transport models show high consistence with the ones obtained from mixture experiments. Based on the results, the transport models provide good predictions for separation and recovery of rare-earth metal ions, which enables operators to choose the optimal experimental parameters more efficiently with certain high selectivity through SLMSD.