The effect of surface chemistry on dissolution rates of CaF₂ suggests a new dissolution mechanism

Jose R. A. Godinho, Sandra Piazolo, Lena Z. Evins

Research output: Contribution to journalMeeting abstract

Abstract

We investigated how during dissolution differences in surface chemistry affect the evolution of topography of CaF₂ pellets with a microstructure similar to UO₂ spent nuclear fuel. 3D confocal profilometry and atomic force microscopy were used to quantify retreat rates and analyze topography changes on surfaces with different orientations as dissolution proceeds up to 468 hours. A NaClO₄ (0.05 M) solution with pH 3.6 which was far from equilibrium relative to CaF₂ was used. Measured dissolution rates depend directly on the orientation of the dissolving surfaces. The {111} is the most stable plane with a dissolution rate of (1.2 ± 0.8) x10⁻⁹ mol.m⁻².s⁻¹ , and {112} the least stable plane with a dissolution rate 33 times faster that {111}. Dissolution rates were found to be correlated to surface orientation which is characterized by a specific surface chemistry and therefore related to surface energy. It was proposed that every surface is characterized by the relative proportions of the three reference planes {111}, {100} and {110}, and by the high energy sites at their interceptions. Based on the different dissolution rates observed and ab initio simulations we propose a dissolution model to explain changes of topography during dissolution. Surfaces with slower dissolution rate, and inferred lower surface energy, tend to form leading to an increase of roughness and surface area. This adjustment of the surface during dissolution suggests that dissolution rates during early stages of dissolution are different from the later stages. The time-dependency of this dynamic system needs to be taken into consideration in geosciences and the nuclear waste disposal management when predicting long-term dissolution rates.
Original languageEnglish
Pages (from-to)1767
Number of pages1
JournalMineralogical Magazine
Volume76
Issue number6
Publication statusPublished - 2012
EventGoldschmidt Conference (22nd : 2012) - Montreal, Canada
Duration: 24 Jun 201229 Jun 2012

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