Role of Electrochemical Surface Potential and Irradiation on Garnet-Type Almandine’s Dissolution Kinetics

Abstract

Nanoscale-resolved quantifications of almandine's (Fe 3 Al 2 (SiO 4 ) 3 ) dissolution rates across a range of pHs (1 ≤ pH ≤ 13)established using vertical scanning interferometryreveal that its dissolution rate achieves a minimum around pH 5. This minimum coincides with almandine's point of zero charge. These trends in almandine's dissolution can be estimated using the Butler−Volmer equation that reveals linkages between surface potentials and dissolution rates, demonstrating proton-and hydroxyl-promoted breakage of Si−O bonds. In contrast to well-polymerized silicates, the dissolution of almandine can also occur through the rupture of its cationic bonds. This behavior is reflected in the observed influences of irradiation on its dissolution kinetics. Molecular dynamics simulations highlight that irradiation induces alterations in the atomic structure of almandine by reducing the coordination state of the cations (Fe 2+ and Al 3+ ), thereby enhancing its reactivity by a factor of two. This is consistent with the minor change induced in the structure of almandine's silicate backbone, whose surface charge densities produce the observed pH dependence (and rate control) of dissolution rates. These findings reveal the influential roles of surface potential arising from solution pH and atomic scale alterations on affecting the reactivity of garnet-type silicates.

The effect of irradiation on the atomic structure and chemical durability of calcite and dolomite

“…8 Such alterations can detrimentally affect the structural integrity of concretean issue of particular importance in nuclear power plants (NPPs). 6,7,[9][10][11] Volume changes produced in nuclear power plant concretes may result from expansion, drying shrinkage, and radiation (e.g., neutron, and γ-rays) effects on the aggregate and cement paste. Aggregates and the minerals therein, which occupy >70% of the volume of concrete and are disproportionately affected by radiation exposure, dominantly affect volume changes and the durability of concrete.…”

“…12,13 Studies of irradiation-induced alterations of the atomic structure and reactivity of minerals have mainly focused on silicates such as quartz: SiO 2 , albite: NaAlSi 3 O 8 , and almandine: Fe 3 Al 2 Si 3 O 12which were observed to form disordered structures following their irradiation. 7,9,10 However, the effects of irradiation on carbonates remain less clear. For example, for calcite, whereas some studies reported negligible changes both in its atomic structure and dissolution kinetics, 7,14 others indicate an evolution toward an amorphous atomic structure with increasing fluence.…”

“…32,34 For example, quartz, albite, and almandine have shown increases in their dissolution rate upon irradiation by a factor of 1000 times, 20 times, and 2 times, respectively. 7,9,10 Effect of irradiation on the atomic structure of carbonate minerals Irradiation can significantly affect the crystal structure of minerals by altering: (i) coordination numbers, (ii) bond lengths, (iii) bond angles, and/or (iv) their medium-range order. 7,9,10 Such alterations and defect formation can produce substantial structural changes, such as loss of crystallinity, i.e., amorphization.…”

“…7,9,10 Effect of irradiation on the atomic structure of carbonate minerals Irradiation can significantly affect the crystal structure of minerals by altering: (i) coordination numbers, (ii) bond lengths, (iii) bond angles, and/or (iv) their medium-range order. 7,9,10 Such alterations and defect formation can produce substantial structural changes, such as loss of crystallinity, i.e., amorphization. Here, vibrational (Fourier-transform Infrared (FTIR) and Raman) spectroscopy techniques were used to evaluate disordering.…”

Rock-Forming Minerals Radiation-Induced Volumetric Expansion – Revisiting Literature Data

“…The mechanistic understanding and quantification of the density change of irradiated minerals is still a topic of ongoing research although recent progress was made thanks to atomistic modeling, e.g., such as molecular dynamics simulations of irradiated quartz, calcite, albite and almandine (Pignatelli et al 2016;Krishnan et al 2017b;Hsiao et al 2017Hsiao et al , 2018. Hence, the development of RIVE models can only be constructed, at this stage, from the empirical observation of the general swelling curves trends with fluence and irradiation temperature.…”