以具分散反萃取相支撐式液膜回收鎳離子之評估

Abstract

在無電鍍鎳程序中，反應所剩餘的廢液，含有未完全反應的鎳離子，故回收具有價值的鎳離子(nickel)，不但可減少汙染，亦可使之重回無電鍍鎳程序中使用。本研究之主要目標，在於開發出可用來回收水溶液中鎳離子的技術，並將其濃縮至可重回無電鍍中使用的濃度。主要以進料溶液模擬無電鍍鎳廢液的陰離子(硫酸根)而得，先以較低濃度的進料做為入門的參考，鎳離子濃度為1000 mg/L -3000 mg/L，其中以1000 mg/L做為研究的主軸。 研究中選擇以酸性萃取劑-二(2-乙基己基)磷酸(D2EHPA)為載體，以Isopar-L做為稀釋劑，首先以具分散反萃取相支撐式液膜來回收鎳離子。研究顯示程序中進料溶液的pH值原為6，在程序一進行進料溶液pH即遽降至2 - 3之間，利用0.6 M D2EHPA只能將進料溶液中的鎳離子由1000 mg/L降至700 mg/L左右，且耗時4小時，而在程序的50分鐘就可以萃取出200 mg/L左右，可知道在50分鐘之後萃取速率慢得多，探討pH值遽降的原因，並由觀察進料溶液的pH值變化，在計算了溶液中氫離子交換濃度後，可知萃取微量的鎳離子釋放出的氫離子可使pH下降速迅，了解到整個系統對pH值是相當敏感的，而選擇以碳酸鈉來提高進料溶液的pH值，使得萃取速率可以維持，並可有效將進料溶液中的鎳離子1000 mg/L完全萃取至有機相，甚至以鎳離子為3000 mg/L亦可以有效的完全萃取。 使用具分散式反萃取相支撐式液膜來回收鎳離子，反萃取相使用5 M H2SO4，期望能以硫酸來高度濃縮鎳離子，但在系統中發現，進料溶液鎳離子濃度為1000 mg/L，在加入鹼於進料溶液來提高pH值，使得程序能完全萃取進料溶液中的鎳離子，而反萃取相所得到的濃縮液，卻無法達到所期望的5倍濃縮，而反萃取濃縮液只濃縮3倍左右，值得探討鎳離子濃度不足以守恆之原因，推測為反萃取不易及水傳遞現象，以期找出方法或條件來提升濃縮效率，在降低了反萃取相的硫酸濃度可使濃縮效率上升，最後可得鎳離子濃縮倍率近5倍。

In terms of the residual wastewater contains no fully reacted nickel ions in electroless nickel process, recover the valuable nickel ions could not only reduce environmental pollution but also reuse them in electroless nickel process. The main purpose of this research is to develop a technique that could be used to recover nickel ions from an aqueous solution and concentrates them to be reusable in electroless nickel process. The feed solution contains 1000-3000 mg/L nickel ions (1000 mg/L, mainly) simulated electroless nickel wastewater of anions (sulfate). In this process, we chose D2EHPA as extractant with diluent Isopar-L. At first, we recovered nickel ions by supported liquid membrane with strip dispersion (SLMSD). The feed solution pH value was 6. Once the process proceeded, the feed solution pH suddenly decreased to 2-3. By using 0.6 M D2EHPA extractant, the concentration of nickel ions could only be decreased from 1000 mg/L to about 700 mg/L in four hours operation. In the first 50 minutes the process could extract 200 mg/L nickel ions, after 50 minutes the extraction rate was much slower. We observed feed solution pH value decrease to calculate how the hydrogen ion exchange to aqueous solution and found out the reason why feed solution pH value decreased drastically was that the small volume hydrogen ions could let the feed solution pH value decreases drastically. We realized that the whole system is very sensitive to the pH value. We used sodium carbonate to increase the feed pH, the feed solution of nickel ions 1000 mg/L completely extracted to the organic phase. 3000 mg/L of nickel ions could also be effect for the complete extraction. We used the supported liquid membrane with strip dispersion to recover nickel ions and 5M H2SO4 aqueous solution as a strip. We expected to get highly concentrated nickel ions by using sulfuric acid, but we found that even though we could fully extract nickel ions via adding base into 1000mg/L concentration nickel ions feed solution to increase pH in the process, we could not meet stripping phase to 5 fold concentration (Actually, 3 fold or so). We conjectured the reasons that broke nickel ions concentration conservation were difficult to stripping and water transfer effect. We improved the efficiency by lower sulfuric acid concentration and results in higher recovery. Finally, we could approach nickel ions concentration to 5 fold.