Kinetics of the Temperature-Dependent eaq- and •OH Radical Reactions with Cr(III) Ions in Aqueous Solutions

The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 degrees C. The reaction between the hydrated electron (e(aq)(-)) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.5 and 3.5 solutions for the first time. This work also studied the reaction between acidic Cr(III) species and the hydroxyl radical ((OH)-O-center dot). It was found that Cr3+ did not react significantly with the (OH)-O-center dot radical, but the first hydrolysis species, Cr(OH)(2+), did with a rate coefficient of k= (7.2 +/- 0.3)x10(8) M-1 s(-1) at 25 degrees C. The oxidation of Cr(OH)(2+) by the (OH)-O-center dot radical formed an absorbing product species that ultimately oxidized to give Cr(VI). These newly measured reaction rates allow for the development of improved models of aqueous chromium speciation for the effective remediation of liquid high-level nuclear waste via vitrification processes.