Preparation of rare earth oxalate ultrafine particles in emulsion liquid membrane system using carboxylic acid as cation carrier

The preparation of oxalate particles of Y and Pr is carried out by using an emulsion liquid membrane (ELM, W/O/W emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as a surfactant and VA-IO (2-methyl-2-ethyl heptanoic acid) as an extractant (cation carrier). The rare earth ions are extracted from the external water phase and are stripped into the internal water phase to precipitate by the reaction with oxalic acid. Oxalate particles, 20-60 nm in size, are obtained for both rare earth elements, together with a smaller amount of submicron-sized spherical aggregates. This result is rather different from that obtained in the ELM system employing EHPNA (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) as an extractant, where oxalate particles of heavier rare earths such as Y are hardly obtained. Calcination of the resulting particles easily gives Y2O3 particles of about 50 mm in size and Pr6O11 particles of submicron-size.