Solubility of Rare Earth Oxalate in Oxalic and Nitric Acid Media

The solubilities of rare earth(Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb) oxalates were measured in nitric acid and oxalic acid media. The concentration of rare earth in the filtrate obtained after oxalate precipitation was determined by ICP-AES. The experiment revealed that the solubilities decreased as the oxalic acid concentration increased and the nitric acid concentration decreased. Based on the assumption that rare earth ions can react with oxalate ion to form RE(C2O4) n3-2n(n = 1,2,3) complex, we have proposed a solubility model of rare earth oxalate. The oxalic acid concentration, the hydrogen ion concentration, and the ionic strength were calculated from the stoichiometric material balances of chemicals in the precipitation reaction. The activity coefficients of ions were also calculated by the modified Debye-Huckel equation. Within the experimental range of oxalate ion activity 1 X 10-8 M to 1 X 10 -5 M, solubility products Ksp and equilibrium constants β1 for rare earth oxalates were obtained.