In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine
Compacted bentonite is currently being considered as a suitable backfill material for sealing underground repositories for radioactive waste as part of a multi-barrier concept. Although showing favorable properties for this purpose (swelling capability, low permeability, and high adsorption capacity...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2021-09-01
|
| Series: | Minerals |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2075-163X/11/10/1082 |
| _version_ | 1797513794304344064 |
|---|---|
| author | Tobias Manzel Carolin Podlech Georg Grathoff Stephan Kaufhold Laurence N. Warr |
| author_facet | Tobias Manzel Carolin Podlech Georg Grathoff Stephan Kaufhold Laurence N. Warr |
| author_sort | Tobias Manzel |
| collection | DOAJ |
| description | Compacted bentonite is currently being considered as a suitable backfill material for sealing underground repositories for radioactive waste as part of a multi-barrier concept. Although showing favorable properties for this purpose (swelling capability, low permeability, and high adsorption capacity), the best choice of material remains unclear. The goal of this study was to examine and compare the hydration behavior of a Milos (Greek) Ca-bentonite sample (SD80) in two types of simulated ground water: (i) Opalinus clay pore water, and (ii) a diluted saline cap rock brine using a confined volume, flow-through reaction cell adapted for in situ monitoring by X-ray diffraction. Based on wet-cell X-ray diffractometry (XRD) and calculations with the software CALCMIX of the smectite d(001) reflection, it was possible to quantify the abundance of water layers (WL) in the interlayer spaces and the amount of non-interlayer water uptake during hydration using the two types of solutions. This was done by varying WL distributions to fit the CALCMIX-simulated XRD model to the observed data. Hydrating SD80 bentonite with Opalinus clay pore water resulted in the formation of a dominant mixture of 3- and 4-WLs. The preservation of ca. 10% 1-WLs and the apparent disappearance of 2-WLs in this hydrated sample are attributed to small quantities of interlayer K (ca. 8% of exchangeable cations). The SD80 bentonite of equivalent packing density that was hydrated in diluted cap rock brine also contained ca. 15% 1-WLs, associated with a slightly higher concentration of interlayer K. However, this sample showed notable suppression of WL thickness with 2- and 3-WLs dominating in the steady-state condition. This effect is to be expected for the higher salt content of the brine but the observed generation of CO<sub>2</sub> gas in this experiment, derived from enhanced dissolution of calcite, may have contributed to the suppression of WL thickness. Based on a comparison with all published wet-cell bentonite hydration experiments, the ratio of packing density to the total layer charge of smectite is suggested as a useful proxy for predicting the relative amounts of interlayer and non-interlayer water incorporated during hydration. Such information is important for assessing the subsequent rates of chemical transport through the bentonite barrier. |
| first_indexed | 2024-03-10T06:21:35Z |
| format | Article |
| id | doaj.art-ec466d6ecd6c4dae80aed8acecac28ce |
| institution | Directory Open Access Journal |
| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-10T06:21:35Z |
| publishDate | 2021-09-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Minerals |
| spelling | doaj.art-ec466d6ecd6c4dae80aed8acecac28ce2023-11-22T19:16:33ZengMDPI AGMinerals2075-163X2021-09-011110108210.3390/min11101082In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock BrineTobias Manzel0Carolin Podlech1Georg Grathoff2Stephan Kaufhold3Laurence N. Warr4Institute of Geography and Geology, University of Greifswald, 17489 Greifswald, GermanyInstitute of Geography and Geology, University of Greifswald, 17489 Greifswald, GermanyInstitute of Geography and Geology, University of Greifswald, 17489 Greifswald, GermanyBundesanstalt für Geowissenschaften und Rohstoffe (BGR), 30655 Hannover, GermanyInstitute of Geography and Geology, University of Greifswald, 17489 Greifswald, GermanyCompacted bentonite is currently being considered as a suitable backfill material for sealing underground repositories for radioactive waste as part of a multi-barrier concept. Although showing favorable properties for this purpose (swelling capability, low permeability, and high adsorption capacity), the best choice of material remains unclear. The goal of this study was to examine and compare the hydration behavior of a Milos (Greek) Ca-bentonite sample (SD80) in two types of simulated ground water: (i) Opalinus clay pore water, and (ii) a diluted saline cap rock brine using a confined volume, flow-through reaction cell adapted for in situ monitoring by X-ray diffraction. Based on wet-cell X-ray diffractometry (XRD) and calculations with the software CALCMIX of the smectite d(001) reflection, it was possible to quantify the abundance of water layers (WL) in the interlayer spaces and the amount of non-interlayer water uptake during hydration using the two types of solutions. This was done by varying WL distributions to fit the CALCMIX-simulated XRD model to the observed data. Hydrating SD80 bentonite with Opalinus clay pore water resulted in the formation of a dominant mixture of 3- and 4-WLs. The preservation of ca. 10% 1-WLs and the apparent disappearance of 2-WLs in this hydrated sample are attributed to small quantities of interlayer K (ca. 8% of exchangeable cations). The SD80 bentonite of equivalent packing density that was hydrated in diluted cap rock brine also contained ca. 15% 1-WLs, associated with a slightly higher concentration of interlayer K. However, this sample showed notable suppression of WL thickness with 2- and 3-WLs dominating in the steady-state condition. This effect is to be expected for the higher salt content of the brine but the observed generation of CO<sub>2</sub> gas in this experiment, derived from enhanced dissolution of calcite, may have contributed to the suppression of WL thickness. Based on a comparison with all published wet-cell bentonite hydration experiments, the ratio of packing density to the total layer charge of smectite is suggested as a useful proxy for predicting the relative amounts of interlayer and non-interlayer water incorporated during hydration. Such information is important for assessing the subsequent rates of chemical transport through the bentonite barrier.https://www.mdpi.com/2075-163X/11/10/1082bentonitewaste repositoriessmectiteswellinghydrationwater content |
| spellingShingle | Tobias Manzel Carolin Podlech Georg Grathoff Stephan Kaufhold Laurence N. Warr In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine Minerals bentonite waste repositories smectite swelling hydration water content |
| title | In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine |
| title_full | In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine |
| title_fullStr | In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine |
| title_full_unstemmed | In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine |
| title_short | In Situ Measurements of the Hydration Behavior of Compacted Milos (SD80) Bentonite by Wet-Cell X-ray Diffraction in an Opalinus Clay Pore Water and a Diluted Cap Rock Brine |
| title_sort | in situ measurements of the hydration behavior of compacted milos sd80 bentonite by wet cell x ray diffraction in an opalinus clay pore water and a diluted cap rock brine |
| topic | bentonite waste repositories smectite swelling hydration water content |
| url | https://www.mdpi.com/2075-163X/11/10/1082 |
| work_keys_str_mv | AT tobiasmanzel insitumeasurementsofthehydrationbehaviorofcompactedmilossd80bentonitebywetcellxraydiffractioninanopalinusclayporewaterandadilutedcaprockbrine AT carolinpodlech insitumeasurementsofthehydrationbehaviorofcompactedmilossd80bentonitebywetcellxraydiffractioninanopalinusclayporewaterandadilutedcaprockbrine AT georggrathoff insitumeasurementsofthehydrationbehaviorofcompactedmilossd80bentonitebywetcellxraydiffractioninanopalinusclayporewaterandadilutedcaprockbrine AT stephankaufhold insitumeasurementsofthehydrationbehaviorofcompactedmilossd80bentonitebywetcellxraydiffractioninanopalinusclayporewaterandadilutedcaprockbrine AT laurencenwarr insitumeasurementsofthehydrationbehaviorofcompactedmilossd80bentonitebywetcellxraydiffractioninanopalinusclayporewaterandadilutedcaprockbrine |