Contrasting coprecipitation and recrystallization mechanisms for Ra immobilization via (Ba,Ra)SO4 solid solution formation in fractured crystalline rocks: Insights from 3D reactive transport modeling.
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| Title: | Contrasting coprecipitation and recrystallization mechanisms for Ra immobilization via (Ba,Ra)SO4 solid solution formation in fractured crystalline rocks: Insights from 3D reactive transport modeling. |
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| Authors: | Wang, Yumeng1 (AUTHOR) geomeng@foxmail.com, Alt-Epping, Peter2 (AUTHOR), Deissmann, Guido1 (AUTHOR), Yang, Yuankai1 (AUTHOR), Hu, Jun3 (AUTHOR), Bosbach, Dirk1 (AUTHOR), Poonoosamy, Jenna1 (AUTHOR) |
| Source: | Geochimica et Cosmochimica Acta. Mar2026, Vol. 417, p211-229. 19p. |
| Subjects: | Coprecipitation (Chemistry), Recrystallization (Chemistry), Crystalline rocks, Solid solutions, Geochemical modeling, Radioactive waste disposal, Radioisotopes |
| Abstract: | Ra incorporation into (Ba,Ra)SO 4 solid solutions is a key control on Ra mobility in groundwater systems and typically occurs through coprecipitation and recrystallization. The effectiveness and persistence of these mechanisms under long-term reactive transport conditions remain poorly constrained, particularly in fractured crystalline rocks, where Ra migration is controlled by the coupled effects of heterogeneous flow, advective–diffusive transport, fracture-matrix mass exchange, reaction kinetics, and evolving hydrogeochemical conditions. Here, we employ 3D reactive transport modeling using PFLOTRAN to investigate Ra mobility under near-field conditions relevant to geological nuclear waste repositories. The models couple fluid flow, solute transport, and non-ideal solid solution-aqueous solution (SS-AS) interactions, incorporating a regular Guggenheim solid solution model and composition-dependent dissolution-precipitation kinetics for stoichiometric solid solutions. Simulations are conducted in a 10 m × 10 m × 10 m fracture-matrix domain upscaled from a discrete fracture network, with a constant-flux inflow boundary and fixed Ra concentration representing a sustained Ra source over 10,000 years. The results show that coprecipitation leads to strong but transient Ra immobilization, with substantial Ra uptake within the first ∼200 years, followed by progressive Ra remobilization as sulfate is depleted and previously formed solid solutions dissolve. Consequently, Ra retention decreases markedly and becomes minimal after ∼1000 years. In contrast, recrystallization supports persistent Ra immobilization throughout the entire 10,000-year simulation period, provided that sufficient barite remains available within fracture zones. This mechanism is sustained by kinetically controlled coupled dissolution-reprecipitation and produces a characteristic spatial zonation, with Ra-rich solid solutions near inflow regions and progressively Ba-rich compositions downstream. Sensitivity analyses further demonstrate that increasing Ba/Ra ratios in the inflowing fluid can reduce the long-term Ra retention under kinetically controlled reactive transport conditions, in contrast to predictions based solely on thermodynamic equilibrium. Fractures are identified as the dominant domains for long-term Ra immobilization, whereas the low-permeability matrix contributes only minimally due to limited diffusive accessibility. Once fractures lose their retention capacity, aqueous Ra is predominantly flushed from the system rather than retained within the matrix. Overall, these results suggest that equilibrium assumptions commonly adopted in radionuclide safety assessments are insufficient to predict Ra behavior in complex subsurface systems, and thus robust evaluation of long-term Ra mobility requires coupling reaction mechanisms and kinetics with flow and transport in evolving fracture-matrix systems. Although both coprecipitation and recrystallization form (Ba,Ra)SO 4 solid solutions, their distinct microscopic mechanisms lead to contrasting long-term behaviors when upscaled to the field scale. These findings have important implications for nuclear waste disposal and managing Ra contamination in geothermal and mining environments. [ABSTRACT FROM AUTHOR] |
| Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
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| Header | DbId: egs DbLabel: Engineering Source An: 192228680 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Contrasting coprecipitation and recrystallization mechanisms for Ra immobilization via (Ba,Ra)SO4 solid solution formation in fractured crystalline rocks: Insights from 3D reactive transport modeling. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Wang%2C+Yumeng%22">Wang, Yumeng</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> geomeng@foxmail.com</i><br /><searchLink fieldCode="AR" term="%22Alt-Epping%2C+Peter%22">Alt-Epping, Peter</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Deissmann%2C+Guido%22">Deissmann, Guido</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Yang%2C+Yuankai%22">Yang, Yuankai</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Hu%2C+Jun%22">Hu, Jun</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Bosbach%2C+Dirk%22">Bosbach, Dirk</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Poonoosamy%2C+Jenna%22">Poonoosamy, Jenna</searchLink><relatesTo>1</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Mar2026, Vol. 417, p211-229. 19p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Coprecipitation+%28Chemistry%29%22">Coprecipitation (Chemistry)</searchLink><br /><searchLink fieldCode="DE" term="%22Recrystallization+%28Chemistry%29%22">Recrystallization (Chemistry)</searchLink><br /><searchLink fieldCode="DE" term="%22Crystalline+rocks%22">Crystalline rocks</searchLink><br /><searchLink fieldCode="DE" term="%22Solid+solutions%22">Solid solutions</searchLink><br /><searchLink fieldCode="DE" term="%22Geochemical+modeling%22">Geochemical modeling</searchLink><br /><searchLink fieldCode="DE" term="%22Radioactive+waste+disposal%22">Radioactive waste disposal</searchLink><br /><searchLink fieldCode="DE" term="%22Radioisotopes%22">Radioisotopes</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Ra incorporation into (Ba,Ra)SO 4 solid solutions is a key control on Ra mobility in groundwater systems and typically occurs through coprecipitation and recrystallization. The effectiveness and persistence of these mechanisms under long-term reactive transport conditions remain poorly constrained, particularly in fractured crystalline rocks, where Ra migration is controlled by the coupled effects of heterogeneous flow, advective–diffusive transport, fracture-matrix mass exchange, reaction kinetics, and evolving hydrogeochemical conditions. Here, we employ 3D reactive transport modeling using PFLOTRAN to investigate Ra mobility under near-field conditions relevant to geological nuclear waste repositories. The models couple fluid flow, solute transport, and non-ideal solid solution-aqueous solution (SS-AS) interactions, incorporating a regular Guggenheim solid solution model and composition-dependent dissolution-precipitation kinetics for stoichiometric solid solutions. Simulations are conducted in a 10 m × 10 m × 10 m fracture-matrix domain upscaled from a discrete fracture network, with a constant-flux inflow boundary and fixed Ra concentration representing a sustained Ra source over 10,000 years. The results show that coprecipitation leads to strong but transient Ra immobilization, with substantial Ra uptake within the first ∼200 years, followed by progressive Ra remobilization as sulfate is depleted and previously formed solid solutions dissolve. Consequently, Ra retention decreases markedly and becomes minimal after ∼1000 years. In contrast, recrystallization supports persistent Ra immobilization throughout the entire 10,000-year simulation period, provided that sufficient barite remains available within fracture zones. This mechanism is sustained by kinetically controlled coupled dissolution-reprecipitation and produces a characteristic spatial zonation, with Ra-rich solid solutions near inflow regions and progressively Ba-rich compositions downstream. Sensitivity analyses further demonstrate that increasing Ba/Ra ratios in the inflowing fluid can reduce the long-term Ra retention under kinetically controlled reactive transport conditions, in contrast to predictions based solely on thermodynamic equilibrium. Fractures are identified as the dominant domains for long-term Ra immobilization, whereas the low-permeability matrix contributes only minimally due to limited diffusive accessibility. Once fractures lose their retention capacity, aqueous Ra is predominantly flushed from the system rather than retained within the matrix. Overall, these results suggest that equilibrium assumptions commonly adopted in radionuclide safety assessments are insufficient to predict Ra behavior in complex subsurface systems, and thus robust evaluation of long-term Ra mobility requires coupling reaction mechanisms and kinetics with flow and transport in evolving fracture-matrix systems. Although both coprecipitation and recrystallization form (Ba,Ra)SO 4 solid solutions, their distinct microscopic mechanisms lead to contrasting long-term behaviors when upscaled to the field scale. These findings have important implications for nuclear waste disposal and managing Ra contamination in geothermal and mining environments. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1016/j.gca.2026.01.045 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 19 StartPage: 211 Subjects: – SubjectFull: Coprecipitation (Chemistry) Type: general – SubjectFull: Recrystallization (Chemistry) Type: general – SubjectFull: Crystalline rocks Type: general – SubjectFull: Solid solutions Type: general – SubjectFull: Geochemical modeling Type: general – SubjectFull: Radioactive waste disposal Type: general – SubjectFull: Radioisotopes Type: general Titles: – TitleFull: Contrasting coprecipitation and recrystallization mechanisms for Ra immobilization via (Ba,Ra)SO4 solid solution formation in fractured crystalline rocks: Insights from 3D reactive transport modeling. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Wang, Yumeng – PersonEntity: Name: NameFull: Alt-Epping, Peter – PersonEntity: Name: NameFull: Deissmann, Guido – PersonEntity: Name: NameFull: Yang, Yuankai – PersonEntity: Name: NameFull: Hu, Jun – PersonEntity: Name: NameFull: Bosbach, Dirk – PersonEntity: Name: NameFull: Poonoosamy, Jenna IsPartOfRelationships: – BibEntity: Dates: – D: 15 M: 03 Text: Mar2026 Type: published Y: 2026 Identifiers: – Type: issn-print Value: 00167037 Numbering: – Type: volume Value: 417 Titles: – TitleFull: Geochimica et Cosmochimica Acta Type: main |
| ResultId | 1 |
