液-液萃取程序廣泛使用於工業上回收重金屬，但在某些條件下，萃取劑會脫離有機溶劑進入水中，形成所謂的「溶出」現象。萃取劑溶出雖不一定會降低重金屬去除率，但會大量增加水中之有機物，造成水質汙染。未來若將萃取程序應用至環工之廢水處理，萃取劑溶出之避免勢必為重要的議題。 影響溶出之因素包括pH值、溶劑量及萃取劑本身特性等。本研究以D2EHPA、TBP及Aliquat336等三種常見之萃取劑進行溶出試驗，探討在不同pH值時之溶出趨勢。重金屬萃取實驗以D2EHPA為主，主要針對銀、鎘及鋅三種不同重金屬進行實驗。 實驗結果指出，純水中之D2EHPA在pH 4後開始大量溶出，至pH 6、7趨近平衡，代表D2EHPA等酸性萃取劑並不適合於高pH值操作。D2EHPA萃取重金屬時可有效減少溶出量，但整體趨勢仍與純水系統相同，實驗D2EHPA萃取重金屬之COD高低為Ag(I)>Zn(II)>Cd(II)。當重金屬濃度增加，水中COD有逐漸下降之趨勢，代表D2EHPA之反應機制為在水中與重金屬結合，形成電中性物質後再回至油相。 相較於D2EHPA，TBP及Aliquat336之溶出受pH影響較小。TBP之溶出為三種萃取劑中最低者；Aliquat336因本身溶解度較高，其溶出皆較酸性條件下之D2EHPA及TBP高，使用Aliquat336所造成之水質汙染實無法避免。 Liquid-liquid extraction was widely used to recover metal in industry. However, the extractant may depart from the organic diluent entering aqueous phase, where the phenomenon is called「extractant dissolution」. Extractant dissolves into aqueous phase not only possibly reducing the extraction efficiency, but also increasing the organic concentration in the treated effluent. Extractant dissolution is affected by several parameters including pH, extractant/diluent weight ratio and solubility of extractant. In this study three commonly used extractants, namely D2EHPA, TBP, and Aliquat336, were employed to test the effect of pH on extractant dissolution. The effect of metals(Ag(I), Cd(II) and Zn(II)) in aqueous phase on extractant dissolution was carried out using D2EHPA. The result showed that dissolution of D2EHPA increased dramatically at pH 4 and reached equilibrium at pH 6 and 7. When dissolution test was conducted with metal-containing water, COD in the aqueous phase decrease, revealing the extractant/metal complexes will re-enter the organic phase resulting in effectively reducing organic content in aqueous phase. The re-entering ability of the extractant/metal complexes is in the the order of Cd>Zn>Ag. COD in aqueous phase decreases with increasing the concentration of metal. Both TBP and Aliquat 336 dissolution is not strongly affected by pH. Dissolution of Aliquat 336 at acidic pH is much higher than TBP and D2EHPA due to the highest water solubility among three extractants investigated. However, the dissolution of D2EHPA in alkalinity condition is the highest.
