This paper describes a chemical processing route of a rare-earth oxide precursor, in which rare-earth carbonate powders are prepared directly from disperse systems of rare-earth-loaded carboxylate solutions and water, using carbon dioxide gas as a precipitant. This synthetic route of rare-earth carbonate is;a combined process of the stripping and precipitation stages,in a conventional solvent extraction. Tertiary carboxylate solutions of lanthanum and yttrium gave precipitates of lanthanum carbonate and yttrium carbonate, when contacted with both water and pure carbon dioxide gas at 10-80 degreesC and 0.1-3.0 MPa for 2 h. The rates of carbonate precipitation-in a batch autoclave were sensitive to processing parameters such as carbon dioxide pressure, temperature, and: organic-phase composition. The particle size distributions of the carbonate powders were markedly dependent on the operating temperature: the mean particle: size of yttrium carbonate drastically decreased from 41 mum at 80 degreesC to 7.2 mum at 10 degreesC.