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Gibbsite and Goethite Solubility

The Influence of 2-Ketogluconate and Citrate

Biosystems Engineering & Environmental Science Dep., Environmental and Soil Sciences Group, 2506 E.J. Chapman Dr., The Univ. of Tennessee, Knoxville, TN 37996-4531

View larger version (22K): [in a new window]   Fig. 1. The structure of 2-keto-D-gluconate.

View larger version (20K): [in a new window]   Fig. 2. Influence of citrate (cit) on the solubility of (a) gibbsite and (b) goethite at ambient temperature (20–22°C). The lines represent the equilibrium solubility of gibbsite and goethite in a 0.05 M NaNO3 solution at 25°C generated using Eq. [14] and Table 1 data.

View larger version (21K): [in a new window]   Fig. 3. Activity diagrams illustrating the activities of Al3+(aq) and Fe3+(aq) as a function of pH relative to the stability of (a) gibbsite and (b) goethite at ambient temperature (20–22°C). Metal cation activities were computed using GEOCHEM-PC and the metal–citrate (cit) binding constants listed in Table 2 (closed symbols, T2) or Table 3 (open symbols, T3). The solid lines represent the equilibrium solubility of gibbsite and goethite at 25°C (Table 1).

View larger version (23K): [in a new window]   Fig. 4. Influence of 2-ketogluconate (kG) and citrate (cit) on the solubility of gibbsite at ambient temperature (20–22°C; SF-4) or 25°C (C31). The line represents the equilibrium solubility of gibbsite in a 0.05 M NaNO3 solution at 25°C generated using Eq. [14] and Table 1 data.

View larger version (26K): [in a new window]   Fig. 5. Influence of 2-ketogluconate (kG) and citrate (cit) on the solubility of goethite at ambient temperature (20–22°C). The line represents the equilibrium solubility of goethite in a 0.05 M NaNO3 solution at 25°C generated using Eq. [14] and Table 1 data.

View larger version (35K): [in a new window]   Fig. 6. Possible structural configurations of Al–2-ketogluconate (kG) and Fe(III)–kG complexes: (a) monodentate and (b) bidentate.

View larger version (23K): [in a new window]   Fig. 7. Activity diagram illustrating the activity of Al3+ as a function of pH at ambient temperature (20–22°C; SF-4) or 25°C (C31). The chemical model defined in Table 4 was used to describe Al–2-ketogluconate (kG) complexation. The solid lines represent the equilibrium solubility of gibbsite at 25°C (Table 1).

View larger version (25K): [in a new window]   Fig. 8. Activity diagram illustrating the activity of Fe3+ as a function of pH at ambient temperature (20–22°C). The chemical model defined in Table 5 was used to describe Fe(III)– 2-ketogluconate (kG) complexation. The solid lines represent the equilibrium solubility of goethite at 25°C (Table 1).

View larger version (30K): [in a new window]   Fig. 9. Predicted species distribution for Al in solutions containing (a) 10–3 M AlT and 10–3 M kGT and (b) 10–4 M AlT and 10–3 M kGT in 0.01 M NaNO3.

View larger version (23K): [in a new window]   Fig. 10. Predicted species distribution for Fe(III) in solutions containing (a) 10–3 M FeT and 10–3 M kGT, and (b) 10–4 M FeT and 10–3 M kGT in 0.01 M NaNO3.