Determination of the parameters of thermodynamic stability constants of bromide complexes of rare earth metals for modeling the optimal regimes of hydrometallurgical extraction

Abstract

Determination of the thermodynamic parameters of complex compounds of rare earth metals in aqueous solutions is of considerable interest for understanding the hydrometallurgical processes associated with the extraction and separation of yttrium and lanthanides from solutions of complex multicomponent composition. The composition of these solutions, as a rule, includes the following anions: SO4 2-, CO3 2-, PO4 3-, F-, which form strong complexes of the inner-sphere type, and anions, which form weak outer-sphere complexes, which primarily include complexes of the metal with halogens Cl-, Br-, I-. By the method of direct potentiometry with the use of a bromide-selective electrode while maintaining the ionic strength constant in the medium of sodium perchlorate, the stability constants (lgK) of the complexes of bromine with cerium, neodymium and samarium at the first stage were determined, the numerical values of which were 0,346; 0,257; 0,387, respectively. Based on the results obtained, the Gibbs energies of formation for the complexes under consideration are calculated. A method is proposed for extrapolating literature or experimental data, which makes it possible to calculate the values of thermodynamic stability constants for the entire series of lanthanides and yttrium. The fundamental possibility of using this method is shown by the example of calculating thermodynamic parameters for bromide complexes of rare-earth metals.