| 摘要: | 聚電解質結合超過濾(PEUF)程序為近幾十年來去除鎳金屬研究之熱門議題，而以往之研究專注於如pH值、不同聚電解質對金屬的負載量(loading rate)、分子截流量(MWCO)，和螯合劑之濃度對於去除重金屬的影響，但是對於同時含有重金屬與聚電解質之PEUF濃縮液要如何處理並沒有多做研究，所以本研究以化學還原法處理PEUF之濃縮液。本研究使用PEI與PSS做為PEUF之聚電解質，測試此兩種聚電解質是否可以去除鎳離子，接著以dithionite做為化學還原法之還原劑，測試各pH值對於鎳的還原有何影響。實驗將使用之廢水分為兩種，一種為以NiSO4‧6H2O製備之人工廢水，另一種為桃園某家PCB廠產生之可能含螯合劑之實廠廢水，測試此技術是否可以整治實廠廢水。
PEUF程序處理鎳研究顯示，當PEI為PEUF之聚電解質時，pH值大於5之後去除率介於83-85%。當PSS為PEUF之聚電解質時，去除率會隨pH值上升而增加，且在pH 9以上去除率可達99%。本實驗之化學還原法分別使用Sodium dithionite (Na2S2O4) 和sodium sulfide (Na2S)處理PEUF濃縮液之鎳離子。以dithionite處理含有PEI之濃縮液時，鎳的去除率在各pH值下皆不超過10%；而當以dithionite處理含有PSS之濃縮液時，在pH 4-pH 9之去除率會隨pH值升高而增加，但在pH 10之後會明顯下降。從PSS system中所回收之固體經由 XRD分析可以知回收固體為Ni3S2，並從TGA分析可以得知在pH 9時所形成之固體有30%為PSS。以Na2S處理含有PSS之濃縮液時，在pH 5-pH 9的條件下，對鎳的去除率皆低於15%。
當PEUF處理可能含有螯合劑之實廠含鎳廢水時，PSS因為電性與金屬螯合物不合，去除率受到pH值很大之限制，在pH 5.4-pH 11之間，鎳的去除率介於20.6-98.2%之間，且經由分析TOC可以知道PEUF無法去除水中之螯合劑。因為PSS作為聚電解質進行PEUF處理程序在pH 11時仍有不錯之去除效果，所以本實驗便將PSS與含鎳實廠廢水混合模擬PEUF之濃縮液，並使用dithionite還原水中的鎳離子。由實驗結果可知，在pH 8-10的條件下鎳之去除率可以達到99%以上，且從XRD與SEM分析可知回收固體與還原人工廢水所產生之固體是相同的。
The PEUF process is frequently studied for the removal of nickels in recent decades. The majority of PEUF studies investigated the metal removal under various operation conditions such as pH, metal loading ratio, types of polyelectrolytes and metals, molecular weight cutoff (MWCO), and concentration of ligands without paying much attention on the treatment of the retentate generated from PEUF which contains both metal and polyelectrolyte. In this study, simultaneous removal and recovery of nickel and regeneration of polyelectrolyte from PEUF retentate by chemical reduction was explored. PEI and PSS were studied to explore their effects on the nickel removal in PEUF and on the nickel recovery by chemical reduction under various pH conditions. With PEI as the polyelectrolyte in PEUF process, the nickel removal efficiency was around 83-85% as the pH value greater than 5. With PSS, PEUF achieves almost 99% nickel removal efficiency as the pH higher than 9, and the nickel removal efficiency increases with increasing pH. Sodium dithionite (Na2S2O4) and sodium sulfide (Na2S) were used to remove nickel from PEUF retentate. With sodium dithionite, the nickel removal efficiency in retentate containing PEI was less than 10% for all pH ranges. For retentate containing PSS, the nickel removal efficiency increased with increasing pH from pH 4-9, and decreased dramatically as the pH higher than 10.The soilds obtained from PSS system were analyzed by XRD with Ni3S2 positively identified. TGA analysis was employed to analyzed the organic content of the obtained solids, showing PSS attached on the particles with weight ratio of 30% at pH 9. Sodium sulfide was also used to remove nickel from PEUF retentate for PSS
system. The result shows that the nickel removal efficiency for pH value ranges from 5-9 were lower than 15 %, indicating that precipitation of Ni by Na2S is not an efficient process.
For real industrial wastewater which might contain organic ligands, the nickel removal efficiency for PEUF process with PSS polyelectrolyte increased from 20.6 to 98.2% when pH increasing from 5.4 to 11. Based on TOC analysis of industrial wastewater and PEUF permeate, organic ligands were not removed by PEUF at all pH ranges. Chemical reduction was used to recover simulated PEUF retentate containing PSS and real industrial wastewater. More than 99% of nickel removal was achieved at pH of 8-10. The obtained solids were subjected with XRD and SEM analysis, and the results are similar to those obtained from chemical reduction of PEUF retentate prepared from synthetic wastewater. |
