The Extraction Of Rare Earth Metal Elements(Europium, Lanthanum) By Microemulsion

In1985, Leung and others had defined "microemulsions" as follows: thermodynamically stable, isotropy, transparent or semitransparent disperse system including two kinds of solution that are immiscible. Microemulsions, which are made from water, organic solvent and surfactant (occasionally cosurfactant) are thermodynamically stable systems. They have unique properties as separation media such as the nanometer-sized spherical or bicontinuous structure and the enhanced solubilization capacity. In this paper, the study is focused on the application of microemulsion on the extraction of europium and lanthanum.First, two stable W/O microemulsion which applied to europium extraction was made from proportionate anionic surfactant (sodium oleate or sodium napthionate), pentanol, heptane and NaCl solution (1mol/L). Various factors which impact the europium extraction yield (E%) had been investigated in this paper, such as contact time, aqueous-microemulsion ratio (R), concentration of sodium oleate (NaOL), extraction temperature, concentration and sort of alcohol, pH of the feed aqueous and concentration of salting-out agent. The result showed that both of these two microemulsion systems had excellent extraction effect on europium, like short balance time, high extraction efficiency, stable phase, and there was not emulsion breaking happen with high aqueous-microemulsion ratio. Europium was probably extracted into the microemulsion phase in the form of Eu(OL)2Cl through slope method(lgD～lgC). The enthalpy and entropy of Eu(III) extraction were calculated to be-12.18kJ/mol and-61.41J/(mol·K) through the thermodynamic calculation, respectively. We found that the extraction temperature had great influence on europium extraction yield, and low temperature was fit for this process.Second, rare earths La(III) had also been studied with those two microemulsion which was thermodynamically stable. Similarly, such as contact time, aqueous-microemulsion ratio (R), concentration of sodium oleate (NaOL), extraction temperature, concentration and sort of alcohol, pH of the feed aqueous and concentration of salting-out agent on lanthanum extraction yield was investigated either. Compared with europium extraction, the effect of temperature on lanthanum extraction was negligible. Lanthanum was probably extracted into the microemulsion phase in the form of La(OL)3Cl3through slope method(lgD～lgC) which slope is close to1.5. The enthalpy and entropy of La(III) extraction were calculated to be-0.7277kJ/mol and-52.58J/(mol-K) through the thermodynamic calculation, respectively.Last, for these two microemulsion with anionic surfactant, the acidity of aqueous had great influence on europium(or lanthanum) extraction yield. It can get a higher extraction rate only under the suitable pH range (3-7). It is precisely because of this, we studied the back-extraction experiments under the condition of high acidity. Different concentrations of hydrochloric acid and sulfuric acid were chosen as stripping. It was found that the stripping effect of hydrochloric acid was better than sulfuric acid under the same concentration of hydrogen ion. But this method made the two microemulsion systems unrecycled because that the microemulsion phase structure is destroyed by adding acid.