The dissolution rates of gibbsite in the presence of chloride, nitrate, silica, sulfate, and citrate in open and closed systems at 20°C |
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| Authors: | M Dietzel G Böhme |
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| Institution: | 1 Institute of Applied Geosciences, Graz University of Technology, Rechbauerstrasse 12, 8010 Graz, Austria
2 Geowissenschaftliches Zentrum der Universität Göttingen, Goldschmidtstrasse 1, 37077 Göttingen, Germany |
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| Abstract: | The dissolution of well crystallized gibbsite far at from equilibrium was studied in batch and mixed flow through reactors. The dissolution experiments were carried out between pH 2 and 6 in the presence of 10 mmol L−1 citrate, at pH 2 and 3 in the presence of 10 mmol L−1 chloride, nitrate, and sulfate, and at pH 2 and 3 in the presence of 1.5 mmol L−1 silica at 20°C. The dissolution rate of gibbsite, RAl (mol m−2 s−1), increases in the order of chloride ≈ nitrate < silica < sulfate ≈ citrate. In presence of silica, sulphate, and citrate dissolution is catalysed by the formation of aluminium complexes at the gibbsite surface (pH 2 and 3). From pH 2 to 3 no effect of RAl on hydrogen activity is predicted as singly coordinated surface sites at the edges of the platy gibbsite crystals, ≡AlOH2+0.5] ≈ ≡AlOH], are almost saturated with protons. However at pH >3 dissolution is slowed by a decrease of ≡AlOH2+0.5].Gibbsite dissolution rates measured in closed and open systems were identical within the experimental and analytical uncertainty. This observation indicates that gibbsite dissolution is a surface controlled process. If dissolution of gibbsite occurs close to equilibrium RAl values may be predicted by an approximately linear function of ΔGr. |
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