Spectrophotometric study of uranyl–oxalate complexation in solution

Abstract

Uranyl–oxalate complex equilibrium in aqueous solution was studied by UV–Vis spectrophotometry. Due to high spectra correlation, derivative spectrophotometry was also applied during the search for the best chemical model. The absorption spectra of all the complexes were calculated and found in a good agreement with theoretical considerations. Overall protonation constants of oxalate, necessary for accurate calculation of uranyl–oxalate formation constants, were also determined under the same conditions and the following values were obtained log K 1=3.83±0.01; log K 2=4.92±0.01. Stability constants determined for the [(UO 2) p (C 2O 4) q ] 2 p−2 q species were: log β 11=6.31±0.02, log β 12=11.21±0.07, log β 13=13.8±0.04, log β 23=18.5±0.2, log β 25=28.5±0.1 ( I=3.0 M NaClO 4; 25 °C). The equilibrium constants were extrapolated to infinite dilution by applying specific ion interaction theory (SIT) and are the following: log β 11 0=7.41±0.01, log β 12 0=11.80±0.02, log β 13 0=13.96±0.07. Formation of polynuclear [(UO 2) 2(C 2O 4) 3] 2− and [(UO 2) 2(C 2O 4) 5] 6− species was proved and confirmed independently by conductometry and vapor pressure osmometry.