Limestone weathering rates accelerated by micron-scale grain detachment

Emmanuel, Simon; Levenson, Yaël

doi:10.1130/g35815.1

Cited by 65 publications

(60 citation statements)

References 32 publications

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“…The resulting datasets inform about material flux from the reacting surface and are analyzed using the rate spectra approach 9,27 . The strength of this relatively new approach has been demonstrated already for polycrystalline material 27 and, consequently, first applications of the concept for such materials have been published [28][29] .…”

Section: Analysis Of Rate Contributorsmentioning

confidence: 98%

Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore

Finkeldei

Brandt

Bosbach

et al. 2015

ACS Appl. Mater. Interfaces

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The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.

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Section: Analysis Of Rate Contributorsmentioning

confidence: 98%

Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore

Finkeldei

Brandt

Bosbach

et al. 2015

ACS Appl. Mater. Interfaces

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show abstract

“…In addition, using vertical scanning interferometry (Fischer et al, 2012;Lüttge et al, 2013), micrite was found to dissolve 1 order of magnitude faster than single calcite crystals. Field-based measurements presented by Emmanuel and Levenson (2014) also showed that micritic limestone weathered significantly faster than coarse grainstone.…”

Section: Impact Of Grain Size On Weathering Ratesmentioning

confidence: 85%

“…be more susceptible to mechanical detachment (Emmanuel and Levenson, 2014). Thus, both the chemical and mechanical effects could make the overall weathering rate strongly dependent on grain size.…”

mentioning

confidence: 99%

Impact of grain size and rock composition on simulated rock weathering

Israeli¹,

Emmanuel²

2018

Earth Surf. Dynam.

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Abstract. Both chemical and mechanical processes act together to control the weathering rate of rocks. In rocks with micrometer size grains, enhanced dissolution at grain boundaries has been observed to cause the mechanical detachment of particles. However, it remains unclear how important this effect is in rocks with larger grains, and how the overall weathering rate is influenced by the proportion of high-and low-reactivity mineral phases. Here, we use a numerical model to assess the effect of grain size on chemical weathering and chemo-mechanical grain detachment. Our model shows that as grain size increases, the weathering rate initially decreases; however, beyond a critical size no significant decrease in the rate is observed. This transition occurs when the density of reactive boundaries is less than ∼ 20 % of the entire domain. In addition, we examined the weathering rates of rocks containing different proportions of high-and low-reactivity minerals. We found that as the proportion of low-reactivity minerals increases, the weathering rate decreases nonlinearly. These simulations indicate that for all compositions, grain detachment contributes more than 36 % to the overall weathering rate, with a maximum of ∼ 50 % when high-and low-reactivity minerals are equally abundant in the rock. This occurs because selective dissolution of the high-reactivity minerals creates large clusters of low-reactivity minerals, which then become detached. Our results demonstrate that the balance between chemical and mechanical processes can create complex and nonlinear relationships between the weathering rate and lithology.

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“…This technique has already been used to examine grain detachment in carbonate rocks (Emmanuel and Levenson, 2014;Levenson and Emmanuel, 2016), although in those previous studies, all experiments were carried out under constant fluid flow. Each sample was prepared from a 5.5 mm diameter core of Solnhofen micritic limestone that was embedded in a Plexiglas disk and polished with an ATM Saphir 520 single wheel grinder with a fluid polishing compound containing one-micrometre diamond particles.…”

Section: Methodsmentioning

confidence: 99%

Repulsion between calcite crystals and grain detachment during water–rock interaction

Levenson¹,

Emmanuel²

2017

Geochem. Persp. Let.

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doi: 10.7185/geochemlet.1714 Weathering in carbonate rocks is often thought to be governed by chemical dissolution. However, recent studies have shown that mechanical detachment of tiny grains contributes significantly to the overall surface retreat. Whether this detachment is caused by shear forces acting at the surface, or repulsive forces acting between grains, was not known. In this study, we used atomic force microscopy to examine the mechanism of grain detachment and we demonstrate that it occurs even in the absence of shearing fluid flow. This suggests that the removal of grains from rock surfaces can be caused by repulsive forces between calcite grains. Although these repulsive forces are expected to be sensitive to the ionic strength of the solution, we did not find enough evidence to demonstrate a correlation between salinity and the frequency of grain detachment. Importantly, our findings suggest that grain detachment occurs during water-rock interaction under low flow conditions over a range of salinities, with potential impacts on geological carbon sequestration and enhanced oil recovery in carbonate formations.

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Limestone weathering rates accelerated by micron-scale grain detachment

Cited by 65 publications

References 32 publications

Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore

Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore

Impact of grain size and rock composition on simulated rock weathering

Repulsion between calcite crystals and grain detachment during water–rock interaction

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