Studies on the solubility and complexation of lanthanum and neodymium fluoride-water systems

The solubilities, solubility products and thermodynamic functions for the LaF3(s)-H2O(1) and NdF3(s)-H2O(1) systems have been measured using conductometric, potentiometric, and radiometric techniques, for comparison with previous results. Our values for Ksp are lower than those reported in literature which varies from 17.1 to 20.2 for LaF3 and 17.1 to 19.9 for NdF3. The standard enthalpy change and standard free energy change for the dissolution of both fluorides are positive. Standard entropy change is, on the other hand negative as obtained from the values of third law entropies of the ionic species in solution as well as a computed positive entropy for LnF3.0.5H2O. The stability constants for the mono- and difluoride complexes of both La and Nd have also bee measured potentiometrically using a simplified approach. (orig.)