Column experiments and full dissolution rate law of gibbsite
- Universidad Central de Venezuela, Caracas (Venezuela)
- Ben-Gurion Univ. of the Negev, Beer-Sheva (Israel)
- Yale Univ., New Haven, CT (United States)
The dissolution of a gibbsitic bauxite in natural systems was simulated in the laboratory, at 25{degrees}C, using a column reactor, with input pHs ranging from 3.2 to 4.5 and fluid velocities ranging from 61 to 1085 m/y. As a result, the dissolution of gibbsite was measured under a wide range of saturation state conditions from equilibrium or near-equilibrium conditions to very far from equilibrium conditions. Far-from-equilibrium dissolution rates were measured under steady-state conditions. At slower flow rates, the variation of the rates with deviation from equilibrium was also extracted. The slowest flow rates yielded the equilibrium solubility of gibbsite. The solubility (K{sub sp}) of natural gibbsite and the column output solution saturation states (expressed as the Gibbs Free Energy of reaction, {Delta}G{sub {gamma}}) were determined with respect to the overall reaction: Al(OH){sub 3} + 3H{sup +} = Al{sup 3} + 3H{sub 2}O. Despite the impurities present in the natural sample material, the calculated log K{sub sp}, 7.83 {plus_minus} 0.12, is in excellent agreement with published K{sub sp} values for pure gibbsite. Far-from-equilibrium, {Delta}G{sub {gamma}} <{minus}0.7 kcal/mol, the dissolution rates attain a constant value of {minus}7.4 {times} 10{sup {minus}13} moles/m{sup 2}/sec at input pH values of 3.5. A reaction order of 0.33 with respect to a{sub H+} was found. The variation of the rates with deviation from equilibrium was found to be very similar to the results of Nagy and Lasaga (1992), even though our study used natural gibbsite, a column device, and different pH and temperature. Therefore, the comparison of the results of this study and Nagy and Lasaga (1992) validates the use of a general rate law and suggests that the same kind of {Delta}G{sub {gamma}} functionality is valid over a broad range of pH and temperature conditions. 45 refs., 11 figs., 6 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 482552
- Journal Information:
- American Journal of Science, Vol. 296, Issue 7; Other Information: PBD: Sum 1996
- Country of Publication:
- United States
- Language:
- English
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