1998 Volume 31 Issue 5 Pages 787-794
The preparation of composite Sr-Pb oxalate particles was carried out by using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as a surfactant and D2EHPA (bis(2-ethylhexyl)phosphoric acid) as an extractant (cation carrier). Sr and Pb ions were extracted from the external water phase and stripped into the internal water phase, to make submicron-sized composite oxalate particles 0.2–0.8 μm in size, which were much smaller than those obtained in homogeneous aqueous solutions. The molar composition of the particles, (Sr/Pb)p, prepared in the ELM system was almost identical to that of the feed external solution, (Sr/Pb)f, and was greater than the molar ratio of the two metals moved to the internal phase, (Sr/Pb)m. This indicates that Sr oxalate precipitates more easily in the internal water droplets, and Pb oxalate is coprecipitated with Sr oxalate. XRD, XPS, thermal analyses, and lattice spacing and lattice strain studies indicate that the particles obtained at (Sr/Pb)f = 20–50 have a structure in which Pb oxalate is finely dispersed in SrC2O4·H2O. Calcination of the oxalate particles obtained gives SrPbO3 or Sr2PbO4, depending on the value of (Sr/Pb)p and calcination temperature.