Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils
The concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption and dissolution–precipitation reactions. Ca binding in calcareous soils depends on the degree of solution saturation with respect to CaCO<sub>3</sub>. Mg may be bound in preci...
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MDPI AG
2022-02-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/12/2/265 |
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| author | Mostafa Abdollahpour Frank Heberling Dieter Schild Rasoul Rahnemaie |
| author_facet | Mostafa Abdollahpour Frank Heberling Dieter Schild Rasoul Rahnemaie |
| author_sort | Mostafa Abdollahpour |
| collection | DOAJ |
| description | The concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption and dissolution–precipitation reactions. Ca binding in calcareous soils depends on the degree of solution saturation with respect to CaCO<sub>3</sub>. Mg may be bound in precipitating calcite. Here, we investigated Mg incorporation into calcite via the recrystallization of vaterite, which simulates a very low supersaturation in a wide range of Mg to Ca ratios and pH conditions. Increasing the Mg to Ca ratios (0.2 to 10) decreased the partition coefficient of Mg in calcite from 0.03 to 0.005. An approximate thermodynamic mixing parameter (Guggenheim <i>a</i><sub>0</sub> = 3.3 ± 0.2), that is valid for dilute systems was derived from the experiments at the lowest initial Mg to Ca ratio (i.e., 0.2). At elevated Mg to Ca ratios, aragonite was preferentially formed, indicating kinetic controls on Mg partitioning into Mg-calcite. Scanning electron microscopy (SEM-EDX) analyses indicated that Mg is not incorporated into aragonite. The thermodynamic mixing model suggests that at elevated Mg to Ca ratio (i.e., ≥1) Mg-calcite becomes unstable relative to pure aragonite. Finally, our results suggest that the abiotic incorporation of Mg into calcite is only effective for the removal of Mg from aqueous environments like calcareous soil solution, if the initial Mg to Ca ratio is already low. |
| first_indexed | 2024-03-09T21:22:09Z |
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| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-09T21:22:09Z |
| publishDate | 2022-02-01 |
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| series | Minerals |
| spelling | doaj.art-dd2aef58545e4c77b9030bbb4bacece62023-11-23T21:19:24ZengMDPI AGMinerals2075-163X2022-02-0112226510.3390/min12020265Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous SoilsMostafa Abdollahpour0Frank Heberling1Dieter Schild2Rasoul Rahnemaie3Department of Soil Science, Tarbiat Modares University, Tehran P.O. Box 14115-336, IranInstitute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, GermanyInstitute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, GermanyDepartment of Soil Science, Tarbiat Modares University, Tehran P.O. Box 14115-336, IranThe concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption and dissolution–precipitation reactions. Ca binding in calcareous soils depends on the degree of solution saturation with respect to CaCO<sub>3</sub>. Mg may be bound in precipitating calcite. Here, we investigated Mg incorporation into calcite via the recrystallization of vaterite, which simulates a very low supersaturation in a wide range of Mg to Ca ratios and pH conditions. Increasing the Mg to Ca ratios (0.2 to 10) decreased the partition coefficient of Mg in calcite from 0.03 to 0.005. An approximate thermodynamic mixing parameter (Guggenheim <i>a</i><sub>0</sub> = 3.3 ± 0.2), that is valid for dilute systems was derived from the experiments at the lowest initial Mg to Ca ratio (i.e., 0.2). At elevated Mg to Ca ratios, aragonite was preferentially formed, indicating kinetic controls on Mg partitioning into Mg-calcite. Scanning electron microscopy (SEM-EDX) analyses indicated that Mg is not incorporated into aragonite. The thermodynamic mixing model suggests that at elevated Mg to Ca ratio (i.e., ≥1) Mg-calcite becomes unstable relative to pure aragonite. Finally, our results suggest that the abiotic incorporation of Mg into calcite is only effective for the removal of Mg from aqueous environments like calcareous soil solution, if the initial Mg to Ca ratio is already low.https://www.mdpi.com/2075-163X/12/2/265magnesium calciteMg to Ca ratiorecrystallizationthermodynamicssolid-solutionpartition coefficient |
| spellingShingle | Mostafa Abdollahpour Frank Heberling Dieter Schild Rasoul Rahnemaie Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils Minerals magnesium calcite Mg to Ca ratio recrystallization thermodynamics solid-solution partition coefficient |
| title | Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils |
| title_full | Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils |
| title_fullStr | Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils |
| title_full_unstemmed | Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils |
| title_short | Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils |
| title_sort | magnesium coprecipitation with calcite at low supersaturation implications for mg enriched water in calcareous soils |
| topic | magnesium calcite Mg to Ca ratio recrystallization thermodynamics solid-solution partition coefficient |
| url | https://www.mdpi.com/2075-163X/12/2/265 |
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