Details
| Original language | English |
|---|---|
| Pages (from-to) | 711-721 |
| Number of pages | 11 |
| Journal | ACS Earth and Space Chemistry |
| Volume | 4 |
| Issue number | 5 |
| Early online date | 10 Apr 2020 |
| Publication status | Published - 21 May 2020 |
Abstract
Anaerobic corrosion at the metal/bentonite interface determines the performance of bentonite-based high-level radioactive waste (HLRW) barriers. Both magnetite and Fe-silicate formation were previously observed as well as higher corrosivity of bentonites containing low-charged smectites. In the present study, six different bentonites containing differently charged smectites were selected and used for laboratory corrosion tests. The extent of corrosion could be quantified based on the mass loss of Fe0, the increase of Fe2+ in the bentonite, and the increase of the total amount of Fe in the bentonite, which was liberated by the native Fe and found in the bentonite afterward. Magnetite and H2 were found, which can be explained, e.g., by the Schikorr reaction, which is often proposed in this context. However, as soon as Si is available in solution, Fe-silicates form. The corrosion is controlled by diffusion, but the extent of the corrosion could be understood based on reactions involving electrons, H2, and Fe2+. An electron reduces water to H2, which then may be consumed by reduction of Fe3+ of the smectites. The reduction of structural Fe3+ in turn can lead to destabilization (dissolution) of the smectites, hence providing Si into solution, which in turn reacts with Fe2+. Based on this finding, it is now possible to explain the previously observed correlation: The correlation with the layer charge density may result from the fact that low-charged smectites are easier to reduce, becoming less stable, hence consuming more H2 and Fe2+, which accelerates the corrosion. Based on this model, it is also possible to explain why sometimes an Fe-silicate coating forms and sometimes magnetite because this depends on the amount of reactive silica, which is naturally present in some bentonites and absent in others.
Keywords
- corrosion mechanism, HLRW bentonite barrier, iron corrosion, reactive silica, smectite alteration, waste repository
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
- Earth and Planetary Sciences(all)
- Atmospheric Science
- Earth and Planetary Sciences(all)
- Space and Planetary Science
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In: ACS Earth and Space Chemistry, Vol. 4, No. 5, 21.05.2020, p. 711-721.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - About the Corrosion Mechanism of Metal Iron in Contact with Bentonite
AU - Kaufhold, Stephan
AU - Klimke, Stephen
AU - Schloemer, Stefan
AU - Alpermann, Theodor
AU - Renz, Franz
AU - Dohrmann, Reiner
PY - 2020/5/21
Y1 - 2020/5/21
N2 - Anaerobic corrosion at the metal/bentonite interface determines the performance of bentonite-based high-level radioactive waste (HLRW) barriers. Both magnetite and Fe-silicate formation were previously observed as well as higher corrosivity of bentonites containing low-charged smectites. In the present study, six different bentonites containing differently charged smectites were selected and used for laboratory corrosion tests. The extent of corrosion could be quantified based on the mass loss of Fe0, the increase of Fe2+ in the bentonite, and the increase of the total amount of Fe in the bentonite, which was liberated by the native Fe and found in the bentonite afterward. Magnetite and H2 were found, which can be explained, e.g., by the Schikorr reaction, which is often proposed in this context. However, as soon as Si is available in solution, Fe-silicates form. The corrosion is controlled by diffusion, but the extent of the corrosion could be understood based on reactions involving electrons, H2, and Fe2+. An electron reduces water to H2, which then may be consumed by reduction of Fe3+ of the smectites. The reduction of structural Fe3+ in turn can lead to destabilization (dissolution) of the smectites, hence providing Si into solution, which in turn reacts with Fe2+. Based on this finding, it is now possible to explain the previously observed correlation: The correlation with the layer charge density may result from the fact that low-charged smectites are easier to reduce, becoming less stable, hence consuming more H2 and Fe2+, which accelerates the corrosion. Based on this model, it is also possible to explain why sometimes an Fe-silicate coating forms and sometimes magnetite because this depends on the amount of reactive silica, which is naturally present in some bentonites and absent in others.
AB - Anaerobic corrosion at the metal/bentonite interface determines the performance of bentonite-based high-level radioactive waste (HLRW) barriers. Both magnetite and Fe-silicate formation were previously observed as well as higher corrosivity of bentonites containing low-charged smectites. In the present study, six different bentonites containing differently charged smectites were selected and used for laboratory corrosion tests. The extent of corrosion could be quantified based on the mass loss of Fe0, the increase of Fe2+ in the bentonite, and the increase of the total amount of Fe in the bentonite, which was liberated by the native Fe and found in the bentonite afterward. Magnetite and H2 were found, which can be explained, e.g., by the Schikorr reaction, which is often proposed in this context. However, as soon as Si is available in solution, Fe-silicates form. The corrosion is controlled by diffusion, but the extent of the corrosion could be understood based on reactions involving electrons, H2, and Fe2+. An electron reduces water to H2, which then may be consumed by reduction of Fe3+ of the smectites. The reduction of structural Fe3+ in turn can lead to destabilization (dissolution) of the smectites, hence providing Si into solution, which in turn reacts with Fe2+. Based on this finding, it is now possible to explain the previously observed correlation: The correlation with the layer charge density may result from the fact that low-charged smectites are easier to reduce, becoming less stable, hence consuming more H2 and Fe2+, which accelerates the corrosion. Based on this model, it is also possible to explain why sometimes an Fe-silicate coating forms and sometimes magnetite because this depends on the amount of reactive silica, which is naturally present in some bentonites and absent in others.
KW - corrosion mechanism
KW - HLRW bentonite barrier
KW - iron corrosion
KW - reactive silica
KW - smectite alteration
KW - waste repository
UR - http://www.scopus.com/inward/record.url?scp=85084423811&partnerID=8YFLogxK
U2 - 10.1021/acsearthspacechem.0c00005
DO - 10.1021/acsearthspacechem.0c00005
M3 - Article
AN - SCOPUS:85084423811
VL - 4
SP - 711
EP - 721
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 5
ER -