- 學位論文
微米氣泡油膜萃取系統去除及回收水中六價鉻重金屬
Removal and recovery of Cr(VI) by compressed air-assisted solvent extraction (CASX)
摘要
萃取程序如LLE、SLM、ELM皆有處理時間冗長、萃取劑容易流失、操作程序繁瑣等問題，而CASX系統因為可產生大量油泡擁有極大的接觸表面積，使得處理時間縮短，且濃縮比例高，因此本研究選擇CASX系統作為萃取程序。 本萃取系統以Aliquat 336當萃取劑，以去除水中含鉻之重金屬廢水，Aliquat 336在水中並不受pH影響，影響其去率高低之因素取決於六價鉻在水中以何種形式存在（HCrO4-或CrO42-）。而當水中若同時有其他陰離子（Cl-或SO42-）存在則會與（HCrO4-或CrO42-）產生競爭萃取劑的現象，使得去除效率降低。 以陶瓷薄膜過濾含Aliquat 336萃取溶劑並不合適，雖然其他研究可以成功過濾含D2EHPA之萃取溶劑，但因Aliquat 336與D2EHPA其物理特性截然不同，使得薄膜內壓力容易累積升高，以及出流水COD偏高。 以NaCl與NaOH混合之脫附劑，在脫附六價鉻反應程序中，Cl-才是主要參與置換的物種，而NaOH只是在改變油相中六價鉻之化合物型態，因為與Aliquat 336結合之能力依序為HCrO4-＞Cl-＞CrO42-。
並列摘要
In this study, Aliquat 336 was used as extractant in CASX system for Cr(VI) removal. The speciation of Aliquat 336 is not affected by pH; however, Cr(VI) species (HCrO4- or CrO42-）are function of pH and have great impact on their removal efficiency. Meanwhile, other anions have slightly influence on Cr(VI) removal with increasing anionic concentration decreasing the removal efficiency of Cr(VI). Although previous study has successfully shown the recovery of D2EHPA-containing solution by ceramic MF membrane, membrane filtration using ceramic membrane is not a suitable option for recovering Aliquat336 due to different physical characteristics of Aliquat 336 and D2EHPA. The relatively high viscosity and solubility of Aliquat336 caused severe membrane fouling and elevated COD in the permeate. Mixtures of NaCl and NaOH were employed as regenerant during regeneration process. Chloride ions are the main species for stripping Cr(VI) from Aliquat336. However, alkaline condition (addition of NaOH) is needed to convert HCrO4- to CrO42- for achieving high regeneration efficiency. It is concluded that the affinity of these ions with Aliquat 336 follow the order of HCrO4-＞Cl-＞CrO42-