Coprecipitation equilibrium of lanthanoid(III) ions with calcium oxalate

The coprecipitation equilibrium of lanthanoid(Ln(III)) ions such as La(III), Ce(III), Nd(III), Sm(III), Tb(III), Tm(III) and Lu(III) with calcium oxalate was investigated by a radiotracer method. The distribution ratio of Ln(III) between the solid phase of calcium oxalate and the aqueous phase containing trace amounts of Ln(III) ions was determined. It was found that the coprecipitation mechanism is an ion exchange of three Ca(II) ions with two Ln(III) ions. The equilibrium constants, K = [Ln3+]solid2[Ca2+]aq3/[Ln3+]aq2, were determined for these 7 lanthanoid ions. (author)