Emulsion and Microemulsion Method

An emulsion liquid membrane (ELM) system has been studied for the selective separation of metals. This system is a multiple phase emulsion, water-in-oil-inwater (W/OAV) emulsion. In this system, the metal ions in the external water are moved into the internal water phase, as shown in Fig, 3.4. The property of the ELM system is useful to prepare size-controlled and morphology controlled fine particles such as metals, carbonates, and oxalates. Rare earth oxalate particles have been prepared using this system, consisting of Span83 (sorbitan sesquioleate) as a surfactant and EHPNA (2-ethyl-hexylphospholic acid mono-2-ethylhexyl ester) as an extractant.In the case of cerium, well-defined and spherical oxalate particles, 20 - 60 nm in size, are obtained. The control of the particle size is feasible by the control of the feed rare earth metal concentration and the size of the internal droplets. Formation of ceria particles are attained by calcination of the oxalate particles at 1073 K, though it brings about some construction of the particles probably caused by carbon dioxide elimination. 

The ELM method is convenient to synthesize fine particles in pm scale but not suitable for the preparation of nanoparticles. The production of single nanometer particles is nowadays one of the most important and attractive technology. Applying 

This method is based on the use of reversed micelles as small reactors. The microemulsion is composed of two immiscible liquids and a surfactant. In water-inoil microemulsions, nanodroplets of aqueous phase within the reversed micelles are dispersed in oil phase. 

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