Aqueous Lanthanum Chloride Speciation to High Temperatures

Abstract

High-temperature aqueous lanthanum chloride speciation is important for modelling the transport of trivalent lanthanides and actinides away from geological waste repositories, and within supercritical water-cooled reactors (SCWR). To determine the species and their equilibrium constants, computational studies, conductivity, and Raman experiments were conducted. Gaussian computational studies predicted four stable aqueous species: La³⁺ (aq), LaCl²⁺ (aq), LaCl₂⁺ (aq) and LaCl₃⁰ (aq). Three species were obtained from the fit of the conductivity data: La³⁺ (aq), LaCl²⁺ (aq) and LaCl₂⁺ (aq). Raman spectra confirmed the presence of these species. Equilibrium constants were obtained from 5 to 275 °C, which showed that LaCl(H₂O)₈²⁺ was dominant at low temperatures and LaCl₂(H₂O)₆⁺ became prevalent at temperatures >150 °C under experimental conditions.