Thermal decomposition features of calcium and rare-earth oxalates

Thermal decomposition of Ln2(C2O4)3 · 9H2O concentrate (Ln = La, Ce, Pr, Nd) in the presence of CaC2O4 · H2O was studied by X-ray diffraction, thermogravimetry, and chemical analysis. Annealing at temperatures above 374°C in the absence of calcium oxalate gives rise to the solid solution of CeO2-based rare-earth oxides. Calcite CaCO3 is formed in the presence of calcium oxalate at annealing temperatures above 442°C, which impedes the formation of lanthanide oxide solid solution and favors crystallization of oxides as individual La2O3, CeO2, Pr6O11, and Nd2O3 phases. An increase in temperature above 736°C is accompanied by decomposition of calcium carbonate to give rise to an individual CaO phase and an individual phase of CeO2-based lanthanide oxide solid solution.