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| Titel |
Quantifying the role of microorganisms in silicate mineral dissolution at the conditions of CO2 storage in basalts |
| VerfasserIn |
Oleg Pokrovsky, Liudmila Shirokova, Gabrielle Stockman, Svetlana Zabelina, Pascale Benezeth, Emmanuelle Gérard, Bénédicte Ménez, Harald Alfredsson |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057936
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| Zusammenfassung |
| Numerous laboratory and field studies indicate that bacteria can significantly affect
aluminosilicate and Al, Fe oxides dissolution rates at the earth-surface conditions. Much less
is known on the effect of bacteria on “basic” Ca, Mg-bearing silicate dissolution rates,
especially in the context of underground setting of CO2 storage sites in basaltic aquifers. This
work reviews our results on olivine (Fo91) and amorphous basaltic glass (β-glass)
dissolution kinetics in batch and mixed-flow reactors in the presence of aerobic
gram-negative bacteria (Pseudomonas reactants, HK 31.3) extracted from deep
underground oxygen-bearing water of basaltic aquifer and in the presence of typical fungi,
Rhodotorula graminis di Menna Y-336T. The release rate of mineral constituents was
measured as a function of time in the presence of live, actively growing, dead cells and
microbial exometabolites in constant-pH (6 to 9), bicarbonate-buffered (0.001 to 0.05
M), nutrient-rich and nutrient-free media in mixed-flow reactors at 0-30 bars of
CO2. Intracellular uptake and reversible surface adsorption of Mg, Si and β-glass
constituents by live and inactivated cells were assessed in growth and adsorption
experiments.
It follows from results of this study that the presence of carbonate/bicarbonate ions and
alkaline solutions (pH -¥ 9), typical for basaltic aquifers, should significantly inhibit the
impact of microbial activity and cell exometabolites on olivine dissolution rate. In acidic,
CO2-saturated solutions at pH < 5 the impact of heterotrophic bacteria is also minor. Only in
neutral, carbonate-free solutions do live but starving cells and dissolved organic ligands
measurably enhance the forward dissolution rates. The effect of P. reactans and Rhodotorula
graminis on major element release during basaltic glass dissolution in all studied
conditions was negligibly small within the experimental reproducibility. This implies an
existence of rather narrow window in which the underground biota may actually affect
basic silicate reactivity at the conditions of CO2 storage. At the typical scenario of
CO2 sequestration in basaltic aquifers, initially acidic, CO2-saturated solutions will
be progressively replaced by neutral, HCO3– bearing solutions. Note that in-situ
carbonate mineralization will decrease the concentration of dissolved inorganic
carbon while maintaining the pH around 7. During this stage of CO2sequestration,
one may expect a pronounced and positive effect of underground biota on mineral
reactivity. Finally, in the post injection period, as the CO2-rich front moves into the
aquifer, pH increases to > 7 following carbonates/silicates dissolution as shown by
reactive transport simulations. At these pH values, the aqueous C-speciation changes
from H2CO3* to HCO3- and CO32- which should results in an inhibition of both
olivine and carbonate mineral dissolution. Noteworthy that aqueous bacteria and
organic ligands are in no way capable of preventing this drop in olivine and calcite
dissolution rate as followed from results of recent studies of mineral dissolution kinetics. |
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