The thermodynamics and kinetics of uranophane dissolution in bicarbonate test solutions

The thermodynamic and kinetic properties of a synthetic uranophane (Ca(H3O) (2)(UO2)(2)(SiO4)(2). 3H(2)O) have been determined from dissolution experim ents in test solutions of different bicarbonate concentrations at 25 degree s C. The experiments were performed using batch and continuously stirred ta nk flow-through reactors. From the experimental data obtained with the batc h reactor the solubility constant for the reaction: Ca(H3O)(2)(UO2)(2)(SiO4 )(2). 3H(2)O + 6H(3)O(+) double left right arrow Ca+2 + 2UO(2)(+2) + 2H(4)S iO(4) + 11H(2)O was determined to be log K-s0(O) = 11.7 +/- 0.6 and the rar e equation for the dissolution process is log r(dissol) (mol s(-1) m(-2)) = -8.3 (+/-0.6) + 0.7 (+/-0.3) log [HCO3-]. By using the continuously stirre d tank flow-through reactor we obtained a rate equation in reasonably good agreement with that obtained in the batch reactor: log r(dissol) (mol s(-1) m(-2)) = -9.2 (+/-0.4) + 0.7 (+/-0.2) log [HCO3-]. Copyright (C) 2000 Else vier Science Ltd.