SOLID LIQUID EQUILIBRIA OF ND3+ IN CARBONATE SOLUTIONS

A redetermination of the solubility products of NdOHCO3(s) and Nd2(CO3)3.(4.5-6)H2O(s) in 0.1 M NaClO4 is presented, extending existing data to a wider variety of CO2, partial pressures and a wider concentration range. NdOHCO3(s) is found in equilibrium with 0.03% and 0.3% CO2 partial pressures; Nd2(CO3)3.(4.5-6)H2O(s) is found in equilibrium with 1.0%, 8.0% and 100% CO2 partial pressures. The solubility products log K(sp)(NdOHCO3) = - 20.12 +/- 0.09 and log K(sp)(Nd2(CO3)3.(4.5-6)H2O) = - 31.54 +/- 0.11 have been determined. Evidence is presented that Nd2(CO3)3.(4.5-6)H2O(S) is probably only metastable in equilibrium with 1.0% CO2 partial pressure. Gibbs free energies of formation have been calculated as DELTAG(f)-degrees-(Nd2(CO3)3(s)) = -3115.9 +/- 4.0 kJ mol-1 and DELTAG(f)-degrees-(NdOHCO3(s)) = -1476.0 +/- 2.9 kJ mol-1.