Kinetics of dissolution of β-uranium trioxide in acid and carbonate solutions
Scott, P.D., Glasser, D. and Nicol, M.J. (1977) Kinetics of dissolution of β-uranium trioxide in acid and carbonate solutions. Journal of the Chemical Society, Dalton Transactions (20). pp. 1939-1946.
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The kinetics of dissolution of β-UO3 in acid and carbonate solutions have been studied as functions of stirring rate, hydrogen-ion concentration, carbonate concentration, various other cations and anions in solution, and temperature. The dissolution rates are: (i) independent of stirring rate, (ii) dependent on the 0.5 order in [H+] in acid solutrons and a substantially lower order in carbonate solutions; (iii) inhibited by the presence of cations in solution in the order Mg2+ > Li+ > Na+ > [NH4]+ > K+[gt-or-equal] Cs+ in acid solutions and Na+ > [NH4]+ > Cs+[gt-or-equal] K+ in carbonate solutions, the relative effects of the cations in the acid and carbonate solutions being very similar; (iv) increased by sulphate but unaffected by chloride, nitrate, and perchlorate ions in acid solutions; and (v) characterised by activation energies of ca. 12 kcal mol–1 in acid solutions and 15 kcal mol–1 in carbonate solutions. The observed kinetic data have been rationalised in terms of a charge-transfer (c.t.) mechanism, in which the transfer of charged complexes of the uranyl and oxide ions of the β-UO3 lattice across the electrochemical-potential barrier at the solid–solution phase boundary is the rate determining step during the dissolution reaction. In HCl, HClO4, and HNO3 the c.t. species are the uranyl and protonated oxide ions of the lattice, while in H2SO4 sulphatouranate complexes are also involved. In carbonate solution the dicarbonatouranate ion and the protonated oxide ion are the c.t. species. The β-UO3 dissolution reactions are interesting examples of c.t. kinetics since the oxide anions and uranyl cations of the β-UO3 lattice form complexes with the cations and anions in the solutions in the process of dissolution and these complex-formation reactions are mirrored in the rate expressions for dissolution.
|Publication Type:||Journal Article|
|Publisher:||Royal Society of Chemistry|
|Copyright:||© 1977 Royal Society of Chemistry|
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