Aluminum speciation and equilibria in aqueous solution: V. Gibbsite solubility at 50[degrees]C and pH 3-9 in 0. 1 molal NaCl solutions (a general model for aluminum speciation; analytical methods)

Journal Article · Fri Jul 01 00:00:00 EDT 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90171-6· OSTI ID:6768151

Wesolowski, D J; Palmer, D A ^[1]

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1. Oak Ridge National Lab., TN (United States)

This study reports 184 new measurements of the solubility of gibbsite at 50[degrees]C and 0.1 molal ionic strength in NaCl solutions of acetate, bistris, and tris buffers with hydrogen ion concentrations ranging from 10[sup [minus]3] to 10[sup [minus]9] molal. Samples collected at 35, 63, 66, 120, and 144 days show no detectable difference in the total aluminum at similar pH values. Correction of the measured solubilities for complexation reactions involving Al[sup 3+] with acetate and Al(OH)[sub 4][sup [minus]] with bistris gives the solubility curve due to Al(OH)[sub y][sup 3-y] species alone, which is smooth and continuous, with a minimum near 10[sup [minus]8] molal (0.3 ppb) and pH 5.5. The corrected solubilities are shown to be in complete agreement with measurements of the same material in more strongly acidic and basic solutions and with the formation constant for Al(OH)[sup 2+] determined potentiometrically by Palmer and Wesolowski. An additional species, Al(OH)[sub 2][sup +], was introduced in order to explain the solubility at pH values around 5.5, and the molal formation quotient for the reaction Al(OH)[sub 3,cr] + H[sup +] [r reversible] Al(OH)[sub 2][sup +] + H[sub 2]O was determined to be 10[sup [minus]3.04[+-]0.05] at 50[degrees]C and 0.1 molal ionic strength. The results of this study were combined with previous results and the new boehmite solubility data of Castet et al. to provide a consistent model for the distribution of monomeric aluminum hydrolysis species and the solubility of gibbsite in 0-5 molal NaCl brines in the 0 to 100[degrees]C range. Acetate complexation is modeled from the results of this study and Palmer and Bell, and is shown to enhance the solubility of gibbsite by more than an order of magnitude in mildly acidic brines containing a few thousand parts per million total acetate, in the absence of competition by other metal ions. A model is presented for aluminum hydrolysis constants at higher temperatures at infinite dilution.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6768151
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:14; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
58 GEOSCIENCES
580000 -- Geosciences
ACETIC ACID
ALUMINIUM COMPOUNDS
ALUMINIUM HYDROXIDES
AQUEOUS SOLUTIONS
BRINES
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
DISPERSIONS
EQUILIBRIUM
GIBBSITE
HYDROGEN COMPOUNDS
HYDROXIDES
MATHEMATICAL MODELS
MINERALS
MIXTURES
MONOCARBOXYLIC ACIDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDE MINERALS
OXYGEN COMPOUNDS
PH VALUE
SOLUBILITY
SOLUTIONS