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Using stable Mg isotope signatures to assess the fate of magnesium during the in situ mineralisation of CO2 and H2S at the CarbFix site in SW-Iceland

Using stable Mg isotope signatures to assess the fate of magnesium during the in situ mineralisation of CO2 and H2S at the CarbFix site in SW-Iceland
Using stable Mg isotope signatures to assess the fate of magnesium during the in situ mineralisation of CO2 and H2S at the CarbFix site in SW-Iceland
The in-situ carbonation of basaltic rocks could provide a long-term carbon storage solution. To investigate the viability of this carbon storage solution, 175 tonnes of pure CO2 and 73 tonnes of a 75% CO2-24% H2S-1% H2-gas mixture were sequentially injected into basaltic rocks as a dissolved aqueous fluid at the CarbFix site at Hellisheidi, SW-Iceland. This paper reports the Mg stable isotope compositions of sub-surface fluids sampled prior to, during, and after the CO2 injections. These Mg isotopic compositions are used to trace the fate of this element during the subsurface carbonation of basalts. The measured Mg isotopic compositions of the monitoring well fluids are isotopically lighter than the dissolving basalts and continue to become increasingly lighter for at least two years after the gas-charged water injection was stopped. The results indicate that the formation of isotopically heavy Mg-clays rather than Mg-carbonates are the predominant Mg secondary phases precipitating from the sampled fluids. Isotope mass balance calculations suggest that more than 70% of the Mg liberated from the basalt by the injected gas charged water was precipitated as Mg-clays, with this percentage increasing with time after the injection, consistent with the continued precipitation of Mg clays over the whole of the study period. The formation of Mg clays in response to the injection of CO2 into basalts, as indicated in this study, could be detrimental to carbon storage efforts because the formation of these minerals consume divalent Mg that could otherwise be used for the formation of carbonate minerals and because such clays could decrease host rock permeability.
0016-7037
542-555
Oelkers, Eric H.
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Butcher, Rhiannon
3cef486f-54ac-4955-83e8-042a6a2d48f2
Pogge Von Strandmann, Philip A.E.
2de2f498-427b-4dcd-a435-ae9253ef20a3
Schuessler, Jan A.
2824de8a-d871-4368-8c3e-84e409d7e232
Von Blanckenburg, Friedhelm
456ffa4e-90bd-41e0-b383-caac515627f6
Snæbjörnsdóttir, Sandra Ó.
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Mesfin, Kiflom
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Aradóttir, Edda Sif
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Gunnarsson, Ingvi
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Sigfússon, Bergur
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Gunnlaugsson, Einar
e09d83ba-3a55-4647-a2ce-2e3692ee0bcf
Matter, Juerg M.
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Stute, Martin
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Gislason, Sigurdur R.
031aa1d2-b345-4e99-9e15-c73f29215e19
Oelkers, Eric H.
3cf51d71-be44-4bed-803e-3b240bdb147b
Butcher, Rhiannon
3cef486f-54ac-4955-83e8-042a6a2d48f2
Pogge Von Strandmann, Philip A.E.
2de2f498-427b-4dcd-a435-ae9253ef20a3
Schuessler, Jan A.
2824de8a-d871-4368-8c3e-84e409d7e232
Von Blanckenburg, Friedhelm
456ffa4e-90bd-41e0-b383-caac515627f6
Snæbjörnsdóttir, Sandra Ó.
72d2bff8-88ff-4d5d-b910-bd0d8e91b839
Mesfin, Kiflom
9c36a273-ef37-452c-bdbe-e13a36632ac1
Aradóttir, Edda Sif
a5113a92-f033-4a40-b758-22c4be703114
Gunnarsson, Ingvi
3ad3a334-8cf4-4bbc-b10a-f18a2d11b577
Sigfússon, Bergur
45616e1a-ee07-434f-8784-ca6d06d5abb9
Gunnlaugsson, Einar
e09d83ba-3a55-4647-a2ce-2e3692ee0bcf
Matter, Juerg M.
abb60c24-b6cb-4d1a-a108-6fc51ee20395
Stute, Martin
1d6a7971-cf3f-48d4-8962-da892b51b25b
Gislason, Sigurdur R.
031aa1d2-b345-4e99-9e15-c73f29215e19

Oelkers, Eric H., Butcher, Rhiannon, Pogge Von Strandmann, Philip A.E., Schuessler, Jan A., Von Blanckenburg, Friedhelm, Snæbjörnsdóttir, Sandra Ó., Mesfin, Kiflom, Aradóttir, Edda Sif, Gunnarsson, Ingvi, Sigfússon, Bergur, Gunnlaugsson, Einar, Matter, Juerg M., Stute, Martin and Gislason, Sigurdur R. (2019) Using stable Mg isotope signatures to assess the fate of magnesium during the in situ mineralisation of CO2 and H2S at the CarbFix site in SW-Iceland. Geochimica et Cosmochimica Acta, 245, 542-555. (doi:10.1016/j.gca.2018.11.011).

Record type: Article

Abstract

The in-situ carbonation of basaltic rocks could provide a long-term carbon storage solution. To investigate the viability of this carbon storage solution, 175 tonnes of pure CO2 and 73 tonnes of a 75% CO2-24% H2S-1% H2-gas mixture were sequentially injected into basaltic rocks as a dissolved aqueous fluid at the CarbFix site at Hellisheidi, SW-Iceland. This paper reports the Mg stable isotope compositions of sub-surface fluids sampled prior to, during, and after the CO2 injections. These Mg isotopic compositions are used to trace the fate of this element during the subsurface carbonation of basalts. The measured Mg isotopic compositions of the monitoring well fluids are isotopically lighter than the dissolving basalts and continue to become increasingly lighter for at least two years after the gas-charged water injection was stopped. The results indicate that the formation of isotopically heavy Mg-clays rather than Mg-carbonates are the predominant Mg secondary phases precipitating from the sampled fluids. Isotope mass balance calculations suggest that more than 70% of the Mg liberated from the basalt by the injected gas charged water was precipitated as Mg-clays, with this percentage increasing with time after the injection, consistent with the continued precipitation of Mg clays over the whole of the study period. The formation of Mg clays in response to the injection of CO2 into basalts, as indicated in this study, could be detrimental to carbon storage efforts because the formation of these minerals consume divalent Mg that could otherwise be used for the formation of carbonate minerals and because such clays could decrease host rock permeability.

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More information

Accepted/In Press date: 8 November 2018
e-pub ahead of print date: 24 November 2018
Published date: 15 January 2019

Identifiers

Local EPrints ID: 426954
URI: http://eprints.soton.ac.uk/id/eprint/426954
ISSN: 0016-7037
PURE UUID: c05c7326-7810-4ab9-84a5-8ba27dc81e62

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Date deposited: 19 Dec 2018 17:30
Last modified: 06 Oct 2020 19:19

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