Effects of pH, extractant/diluent ratios, and metal concentrations on the extent of extractant dissolution during liquid–liquid extraction were investigated. Experimental result shows that D2EHPA dissolution increases dramatically at pH above 4, leveling off at pH 6–7. The phenomenon is consistent with deprotonation of D2EHPA and the domination of negatively charged D2EHPA species at pH of higher than 4. Concentration of D2EHPA in the aqueous phase, i.e., the extent of extractant dissolution, drops after addition of metal and decreases with increasing metal concentration. The amount of D2EHPA ‘re-entering’ the organic phase is calculated to be 2.04 mol per mol of Cd added, which is quite closed to the stoichiometric molar ratio of 2 between D2EHPA and Cd via ion exchange reaction. The effect of metal species on the extent of extractant/metal complexes re-entering is in the order of Cd≈Zn >Ag, which might be coincident to the complexation stability of these metals with D2EHPA. The extent of extractant dissolution in liquid–liquid extraction process depends on the type and concentration of metal to be removed, pH of aqueous phase, and extractant/diluent ratios. 本研究中探討酸鹼度(PH) ，萃取液與稀釋液的比例，及重金屬濃度對液相-液相萃取系統中萃取液溶出的影響。實驗結果顯示D2EHPA於pH4 大量的溶出至pH6-7 達到平衡。此現象與D2EHPA 去質子化及於pH>4 帶負電物種為主之情況一致。D2EHPA 於液相的濃度(萃取液溶出)因加入金屬而降低且隨著加入金屬濃度的增加而減少。D2EHPA 再次進入有機溶液相的比例濃度為2.04 莫耳(mol) 每莫耳加入的鎘(Cd) ，比比例數值相當接近經由離子交換反應的化學計量數值2 之比例。金屬物種對於萃取液與金屬複合物再溶出的影響程度為Cd≈Zn> Ag，此原因可能與金屬結合D2EHPA 之複合物的穩定性有關。液相-液相萃取程序中萃取液溶出的程度取決於欲萃取之金屬物種及濃度，液相的pH 值，及萃取液與稀釋液的比例。
