Surfactant Gel Extraction of Metal Ammine Complexes using SDS and KCl at Room Temperature, and a Small-angle X-ray Diffraction Study of the Surfactant Phase

Abstract

Micellar solutions of sodium dodecylsulfate (SDS) exhibit the property of being separated into two phases as a result of a temperature change or the addition of salts. Upon addition of KCl to an SDS solution, the surfactant phase of Na⁺DS^- changed to the potassium dodecylsulfate phase of K⁺DS^- (KDS) at room temperature around 25°C. The ammine complexes of metal ions such as copper reacted with the dodecylsulfate anion (DS^-) to form the corresponding ion pair, and were separated from the solution as the surfactant phase. After the phase separation of the solution containing SDS, KCl, ammonia, and copper, the surfactant phase consisted of KDS and the ion pair of [Cu(NH₃)₄^2＋](DS^-)₂ (abbreviated CuDS). The structures of the surfactant phases were investigated by small-angle X-ray diffraction (SAXRD) and differential scanning calorimetric measurements. The surfactant phases had lamellar structures with layer distances (d₍₀₀₁₎) of 3.4 nm for KDS and 2.4 nm for CuDS. This surfactant gel extraction method was applied to the mutual separation of copper and zinc in a brass alloy. The extractability of the metals was regulated by the initial metal concentration in the sample solution. The percent extraction was (98.7 ± 0.6)% and (6.8 ± 1.4)% for copper and zinc, respectively.