Microemulsion Extraction Of Samarium

Microemulsions, which are made from water, an organic solvent, a surfactant and occasionally a cosurfactant, are thermodynamically stable systems. They have unique properties as separation media such as the nanometer-sized spherical or bicontinuous structure, the rapid coalescence and reseparation dynamics of the structure and the enhanced solubilization capacity.First, the influence of the concentration of sodium oleate, alcohol and the nature of the internal water phase on the water content of microemulsion was stuied. It is found that: the water concent of mircoemulsion increased as a straight line basically with the increase of the NaOL concentration. It first increased to a maximum and then decreased sharply, with a subsequent slow decrease to a flatform with the increase of the alcohol concentration. The addition of acid, base or salt into the in ternal water phase would reduce the water concent of mircoemulsion. The structural paraneters of sodium oleate microemulsion, inner water radius R_w, effective radium R_e, length of interface L, average aggregation number N,total number of particles N_d, and total interfacial area of dispersed phase A_d, were calculated based on dilution method. The change of standard free energy â–³G^o_c-I for the alcohol to transfer from the continuous phase to the interface membranes was also calculated. It is found that with the increase of water uptake of the formed microemulsion, R_w increased linearly, N and â–³G^o_c-I decreased, and the microemulsion became unstable. The variations of electric conductivity of microemulsion with the alcohol species and the salinity of internal water during the solubilization process were determined. The results support the cation conduction mechanism of W/O microemulsion. It is found that the micro emulsion was more stable when using short chain alcohols as cosurfactant.In the next section, the microemulsions prepared were used for the extraction of samarium(III). The effect of the concentraction of surfactant, alcohol, salting-out agent, extractant added and of contact time,volume ratio of aqueous to microemulsion (R) and temperature on the extraction yield was investigated. The result shows that the extraction of samarium is effective under well-defined conditions utilizing Winsor II microemulsioin systems. The extraction yield inceased with the increase of alcohol concentration first and then reduced, reduced with the increase of temperature and had a maximum with the increase of salting-out agent concentration. The addition of TBP, MIBK, N503 into the microemulsion will reduce the extraction yield, but the addition of N235 will improve the extractin. The separation of Sm(III) and Co( II) us ing microemulsion was investigated. It is found that the two metal ions will be separated well(β_Sm/Co=132.26) at proper sodium oleate concentration.At last, the extraction mechanism of metal ions by NaOL microemulsion system was discussed via the investigation on the nature of the load saturation organic phase of different metal ions (Sm³⁺, Ni²⁺, Co²⁺, Ca²⁺ and Mg²⁺, respectively). The FT-IR spectra, electric conductivity (c) and coloring by xylenol organe of the load saturation organic phase were investigated. The result showed that the extraction of Sm³⁺, Co²⁺ and Ni²⁺ with NaOL microemulsion may be an ion-exchange reaction with Na⁺. The reaction product is a stable hydrophobic chelate complex of metal ions and OL^-. In addition, this chelate complex, with no surface activety to form a microemulsion, dissolves in the continuous organic phase. However, the extraction of Ca²⁺ and Mg²⁺ may be achieved mainly through an electrostatic attraction effect. The metal ions and OL^- exist in a form of ion-pair compounds, which can also form W/O microemulsions. Based on the discussion of the extraction mechanism, we inferred the possible structure of the extractants.