Uranium and Lanthanide Speciation by Thermal Lensing Spectrometry

Abstract

THE CHARACTERIZATION OF AQUEOUS SPECIES IN WATER-ROCK SYSTEMS IS ESSENTIAL TO ELUCIDATE CONDITIONS AND EXTENT OF RADIONUCLIDE REACTIONS IN GEOCHEMICAL PROCESSES SUCH AS ORE FORMATION OR MIGRATION FROM NUCLEAR WASTE REPOSITORIES. PROGRESS IN MEASURING SPECIES CONCENTRATIONS IS GENERALLY HINDERED BY THE LOW SOLUBILITIES OF ACTINIDE AND LANTHANIDE COMPOUNDS WITH NATURAL LIGANDS. CON- SEQUENTLY, HIGH SENSITIVITY METHODS ARE REQUIRED TO INVESTIGATE DISSOLVED SPECIES AT REALISTIC CONCENTRATION LEVELS. THE HEAT-INDUCED REFRACTIVE INDEX CHANGE CAUSED BY ABSORPTION OF A PULSED DYE LASER RADIATION BY SOLUTION SPECIES, WAS USED TO INVESTIGATE THE CONVERSION OF URANIUM AND LANTHANIDE FREE IONS TO COMPLETE COMPLEXATION IN NEUTRAL AND CARBONATE SOLUTIONS. A HE-NE LASER WAS USED AS A PROBE BEAM IN A CONVENTIONAL DUAL BEAM CONFIGURATION WHERE THE BEAM WAISTS ARE INDEPENDENTLY ADJUSTED. ABSORPTION AS SMALL AS 10-5 CM-1 CORRESPONDING TO A DETERMINATION LIMIT OF 5X10-7 M FOR U(VI) CARBONATE COMPLEXES WERE MEASURED BY THE THERMAL LENS TECHNIQUE. THE TUNABILITY OF THE LASER SOURCE ALLOWED TO OBTAIN SPECTRA AT CONCENTRATIONS BELOW THE LIMIT IMPOSED BY THE SOLUBILITY CONTROLLING SOLID PHASES