Effect of pH and organic ligands on the kinetics of smectite dissolution at 25 °C |
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Authors: | Sergey V. Golubev Oleg S. Pokrovsky |
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Affiliation: | a Aqueous Experimental Geochemistry and Biogeochemistry Group, UMR 5563 CNRS—Observatoire Midi-Pyrénées, Université Paul-Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France b Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, INE, P.O. Box 3640, 76021 Karlsruhe, Germany |
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Abstract: | Forward dissolution rates of Na-Montmorillonite (Wyoming) SWy-2 smectite (Ca0.06Na0.56)[Al3.08Fe(III)0.38Mg0.54] [Si7.93 Al0.07]O20(OH)4 were measured at 25 °C in a mixed-flow reactor equipped with interior dialysis compartment (6-8 kDa membrane) as a function of pH (1-12), dissolved carbonate (0.5-10 mM), phosphate (10−5 to 0.03 M), and nine organic ligands (acetate, oxalate, citrate, EDTA, alginate, glucuronic acid, 3,4-dihydroxybenzoic acid, gluconate, and glucosamine) in the concentration range from 10−5 to 0.03 M. In organic-free solutions, the Si-based rates decrease with increasing pH at 1 ? pH ? 8 with a slope close to −0.2. At 9 ? pH ? 12, the Si-based rates increase with a slope of ∼0.3. In contrast, non-stoichiometric Mg release weakly depends on pH at 1 ? pH ? 12 and decreases with increasing pH. The empirical expression describing Si-release rates [R, mol/cm2/s] obtained in the present study at 25 °C, I = 0.01 M is given by |
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