SOLUBILITY OF SELECTED LANTHANIDE OXIDES USED AS NEUTRON POISONS: DYSPROSIUM OXIDE, HOLMIUM OXIDE AND GADOLINIUM OXIDE

摘要

The solubility of three lanthanide oxides, dysprosium oxide (Dy Dy2O3), holmium oxide (Ho ), Ho2O3) and gadolinium oxide (Gd ) Gd2O3) in aqueous solutions was investigated as a function of pH, temperature and time. Solid oxide powders were equilibrated in aqueous solutions of known initial pH for various times at controlled temperatures. The experiments were carried out with solutions of pH values varying from 3 to 12 at temperatures between 20 ) ○C and 80 ○C for time periods from ~3 h to ~500 h. At the end of an experiment, the concentrations of the lanthanide oxides in solution were determined using Inductively Coupled Plasma-Mass Spectrometry (ICPMS) or Inductively Coupled Plasma-Atomic Emissions Spectrometer (ICP-AES). There was inverse exponential dependence between the metal ion concentration and pH for the pH range 3 to 10.3. All three oxides are very soluble in acidic solutions but have very low solubility in water at pH 10.3, the approximate pH of the coolant in CANDU ? reactors. There was no measurable difference in the solubility of these metal oxides for solutions of pH 10.3 and 12.0. The exposure time and temperature, for the time periods and the temperatures used in this work, had a minimal effect on the concentrations of the dissolved oxides.