| The application of microemulsions for the extraction of metals seems an exciting and promising technique which has been developed during last more than ten years. Microemulsion is an optically isotropic, transparent, and thermodynamically stable system formed spontaneously from surfactants, cosurfactants, oil and water or aqueous solution. Generally, at the point of view of phase dispersion, microemulsion can broadly be divided into three types, i.e. the water-in-oil microemulsion (W/O), oil-in-water microemulsion (O/W) and bi-continuous microemulsion that related to value of the hydrophilic-lipophilic balances of surfactants used. It may also be fall into four categories: 1. dispersion of O/W microemulsion equilibrium with excess oil (Winsor I ); 2.dispersion of W/O microemulsion equilibrium with excess water (Winsor II );3.both O/W and W/O microemulsion(or bi-continuous microemulsion) equilibrium with both oil and water(WinsorIII);4.a homogeneous single phase of dispersion either O/W or W/O not in contact with any other phase(WinsorⅣ).Metal extraction from aqueous solution using microemulsions needs to becarried out in Winsor II system, so the phase behavior of microemulsion systems were firstly investigated by drawing their Pseudo-ternary phase diagrams in the present thesis. The microemulsion selected in this work is composed of OP-7[Polyoxyethylene (7) nonylphenol] and OP-4[Polyoxyethylene (4) nonylphenol], benzylacohol, kerosene, D2EHPA[di(2-ethylhexyl) phosphoric acid ] as well as HC1 solution, in which OP-7 and OP-4 are nonionic surfactants; benzylacohol is acted as co-surfactant; D2EHPA is an extractant (also called mobile carrier in the liquid membrane system); kerosene is the diluter, and HC1 solution acted as striping agent in the receiving phase of microemulsion. The results showed that the ion-exchanger-free microemulsion system (OP-7 + OP-4)/benzylacohol/ kerosene/HCl was favorite to forming WinsorⅢ system. While the desired Winsor II system was easily obtained by adding D2EHPA to this microemulsion.The properties of the microemulsion system (OP-7+OP-4)/ benzylacohol/ D2EHPA kerosene/HCl, such as the solubilization, viscosity and the interfacial behavior of surface activity agents, i.e. OP-7, OP-4, benzylacohol and D2EHPA, were studied in succession. This is because higher content of HC1 solution and moderate viscosity are required for microemulsions while they are used for extraction. The results repeal that the solubilization of HC1 solution in the microemulsions increase with the increasing of mass ratio of OP-7 to OP-4, of mixed surfactants (OP-7+OP-4) to benzylacohol and of HC1 solution concentrations. Similarly, the viscosity of the microemulsion increases with anincrease of HC1 solution concentrations. The interfacial activities of four agents are in the order OP-7>OP-4>D2EHPA>benzylacohol, and their cross-section area on the 1/1 interface are 67.8×10-20, 55.2×10-20,47.3×10-20, 115.4× 10-20(m2) respectively while the maximum adsorption amount are reached.The W/O nonionic microemulsion, on one hand, is a thermodynamic equilibrium system that is the same as the traditional solvent extraction system; on the other hand, it is no limited by equilibrium constant while it is used for extraction. Compared with emulsion liquid membrane, this microemulsion not only poses the advantage of high effect of separation but also over comes the membrane disruption and swollen arisen of thermodynamic instability of emulsion liquid membrane. Unfortunately, the serious leakage of solutes from receiving phase to source phase occurred in the disperse process of the microemulsion. The direct consequence for this is that solutes enrichment in receiving phase is poor. To solving this problem, a novel extraction technique using a W/O nonionic microemulsion within a hollow-fiber-contactor(HFC) for the extraction and enrichment of neodymium has been developed in this paper. The used microemulsion system is (OP-7+OP-4)/benzylacohol/D2EHPA/kerosene /HC1. The hollow-fiber membrane material is...
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