Experimental study of the effect of pH on the kinetics of montmorillonite dissolution at 25 °C

Abstract The effect of pH on the kinetics of smectite (K-montmorillonite) dissolution was investigated at 25 °C in batch and stirred flow-through reactors over the pH range of 1–13.5, in KNO3 solutions. Dissolution rates were obtained based on the release of Si and Al at steady-state under far from equilibrium conditions. Dissolution was non-stoichiometric between pH 5 and 10, due to adsorption/precipitation of Al. Dissolution rates computed from batch and flow-through experiments were consistent, irrespective of the Si and Al concentrations. Sample pre-treatment and the interlayer cation do not affect the steady-state dissolution rate or stoichiometry of cation release. The rate dependence on pH can be described by: R ( molm - 2 s - 1 ) = 10 - 12.30 a H + 0.40 + 10 - 14.37 + 10 - 13.05 a OH - 0.27 The experimental results are consistent with a dissolution mechanism involving inward movement of a dissolution front from crystal edges. Consequently, normalization of the dissolution rates should take into account the reactive surface located on the smectite edges.

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