Column experiments and the full dissolution rate law of gibbsite

Abstract

The dissolution of a gibbsitic bauxite in natural systems was simulated in the laboratory, at 25°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 (Ksp) of natural gibbsite and the column output solution saturation states (expressed as the Gibbs Free Energy of reaction, ΔGr) were determined with respect to the overall reaction: Al(OH)3 + 3H+ = Al3+ + 3H2O Despite the impurities present in the natural sample material, the calculated log Ksp, 7.83 ± 0.12, is in excellent agreement with published Ksp values for pure gibbsite. Far-from-equilibrium, ΔGr