Department of Water Resources and Environmental Engineering, Tamkang University, 151 Ying-Chuan Road, Tamsui district 25137, New Taipei city, Taiwan.
Water Res. 2011 Nov 15;45(18):5953-8. doi: 10.1016/j.watres.2011.08.054. Epub 2011 Sep 7.
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 D(2)EHPA dissolution increases dramatically at pH above 4, leveling off at pH 6-7. The phenomenon is consistent with deprotonation of D(2)EHPA and the domination of negatively charged D(2)EHPA species at pH of higher than 4. Concentration of D(2)EHPA 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 D(2)EHPA '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 D(2)EHPA 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 D(2)EHPA. 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.
研究了 pH 值、萃取剂/稀释剂比以及金属浓度对液-液萃取过程中萃取剂溶解程度的影响。实验结果表明，在 pH 值高于 4 时，D(2)EHPA 的溶解急剧增加，在 pH 值为 6-7 时趋于稳定。这一现象与 D(2)EHPA 的去质子化和 pH 值高于 4 时带负电荷的 D(2)EHPA 物种的主导地位一致。水相中的 D(2)EHPA 浓度，即萃取剂的溶解程度，在加入金属后下降，并随金属浓度的增加而降低。计算得出，每加入 1 摩尔 Cd，有 2.04 摩尔的 D(2)EHPA“重新进入”有机相，这与通过离子交换反应 D(2)EHPA 和 Cd 的化学计量摩尔比 2 非常接近。金属种类对萃取剂/金属配合物重新进入有机相的影响顺序为 Cd≈Zn＞Ag，这可能与这些金属与 D(2)EHPA 的络合稳定性一致。液-液萃取过程中萃取剂的溶解程度取决于要去除的金属的类型和浓度、水相的 pH 值以及萃取剂/稀释剂比。
