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Olivine Dissolution in Seawater: Implications forCO 2 Sequestration through Enhanced Weathering in CoastalEnvironments

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ABSTRACT

Enhanced weathering of (ultra)basic silicate rocks such as olivine-richdunite has been proposed as a large-scale climate engineering approach.When implemented in coastal environments, olivine weathering is expectedto increase seawater alkalinity, thus resulting in additional CO2 uptake from the atmosphere. However, the mechanisms of marineolivine weathering and its effect on seawater–carbonate chemistryremain poorly understood. Here, we present results from batch reactionexperiments, in which forsteritic olivine was subjected to rotationalagitation in different seawater media for periods of days to months.Olivine dissolution caused a significant increase in alkalinity ofthe seawater with a consequent DIC increase due to CO2 invasion,thus confirming viability of the basic concept of enhanced silicateweathering. However, our experiments also identified several importantchallenges with respect to the detailed quantification of the CO2 sequestration efficiency under field conditions, which includenonstoichiometric dissolution, potential pore water saturation inthe seabed, and the potential occurrence of secondary reactions. Beforeenhanced weathering of olivine in coastal environments can be consideredan option for realizing negative CO2 emissions for climatemitigation purposes, these aspects need further experimental assessment.

No MeSH data available.


(A) Model results of both absolute and relative cumulative dissolutionover time (using dissolution rate constant values as obtained fromthe experiments in this study) of a one-time hypothetical coastalolivine application of 12 Mm3, or 26.4 Mton, of olivinesand with the same characteristics as that used here. (B) Model resultsof the yearly CO2 uptake rate as a consequence of hypotheticalrepeated (multiyear) olivine application as a substitute for yearlycoastal sand nourishments during periods of 1, 5, 10, and 25 years.
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fig5: (A) Model results of both absolute and relative cumulative dissolutionover time (using dissolution rate constant values as obtained fromthe experiments in this study) of a one-time hypothetical coastalolivine application of 12 Mm3, or 26.4 Mton, of olivinesand with the same characteristics as that used here. (B) Model resultsof the yearly CO2 uptake rate as a consequence of hypotheticalrepeated (multiyear) olivine application as a substitute for yearlycoastal sand nourishments during periods of 1, 5, 10, and 25 years.

Mentions: In a thought experiment, the sand used in these coastalnourishments is replaced by finely ground olivine, as used in theexperiments described here. In a hypothetical one-time applicationof 12 Mm3 (≈ 26 Mt) of olivine sand, parameter valuesfor kΔTA obtained in our experiments(Table 1) were implementedin the Olsen53 shrinking core model forolivine carbonation (assuming the measured olivine particle size distribution;see section 2 of the Supporting Information). This model has been previously implemented in ten Berge et al.,54 describing total mass of olivine weathered andconsequential CO2 captured (section 8 of the Supporting Information). Our simulations showed acumulative weathering of 4% of the olivine after the first year, 12%after 5 years, 35% after 25 years, 57% after 50 years, and 84% after100 years (Figure 5A). After 200 years, 98% of the initially applied 12 Mm3 olivine will be dissolved. These values are in accordance with thosepresented by Hangx and Spiers,14 in which100 μm (median diameter: D50) olivinegrains would take >100 years to dissolve.


Olivine Dissolution in Seawater: Implications forCO 2 Sequestration through Enhanced Weathering in CoastalEnvironments
(A) Model results of both absolute and relative cumulative dissolutionover time (using dissolution rate constant values as obtained fromthe experiments in this study) of a one-time hypothetical coastalolivine application of 12 Mm3, or 26.4 Mton, of olivinesand with the same characteristics as that used here. (B) Model resultsof the yearly CO2 uptake rate as a consequence of hypotheticalrepeated (multiyear) olivine application as a substitute for yearlycoastal sand nourishments during periods of 1, 5, 10, and 25 years.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382570&req=5

fig5: (A) Model results of both absolute and relative cumulative dissolutionover time (using dissolution rate constant values as obtained fromthe experiments in this study) of a one-time hypothetical coastalolivine application of 12 Mm3, or 26.4 Mton, of olivinesand with the same characteristics as that used here. (B) Model resultsof the yearly CO2 uptake rate as a consequence of hypotheticalrepeated (multiyear) olivine application as a substitute for yearlycoastal sand nourishments during periods of 1, 5, 10, and 25 years.
Mentions: In a thought experiment, the sand used in these coastalnourishments is replaced by finely ground olivine, as used in theexperiments described here. In a hypothetical one-time applicationof 12 Mm3 (≈ 26 Mt) of olivine sand, parameter valuesfor kΔTA obtained in our experiments(Table 1) were implementedin the Olsen53 shrinking core model forolivine carbonation (assuming the measured olivine particle size distribution;see section 2 of the Supporting Information). This model has been previously implemented in ten Berge et al.,54 describing total mass of olivine weathered andconsequential CO2 captured (section 8 of the Supporting Information). Our simulations showed acumulative weathering of 4% of the olivine after the first year, 12%after 5 years, 35% after 25 years, 57% after 50 years, and 84% after100 years (Figure 5A). After 200 years, 98% of the initially applied 12 Mm3 olivine will be dissolved. These values are in accordance with thosepresented by Hangx and Spiers,14 in which100 μm (median diameter: D50) olivinegrains would take >100 years to dissolve.

View Article: PubMed Central - PubMed

ABSTRACT

Enhanced weathering of (ultra)basic silicate rocks such as olivine-richdunite has been proposed as a large-scale climate engineering approach.When implemented in coastal environments, olivine weathering is expectedto increase seawater alkalinity, thus resulting in additional CO2 uptake from the atmosphere. However, the mechanisms of marineolivine weathering and its effect on seawater–carbonate chemistryremain poorly understood. Here, we present results from batch reactionexperiments, in which forsteritic olivine was subjected to rotationalagitation in different seawater media for periods of days to months.Olivine dissolution caused a significant increase in alkalinity ofthe seawater with a consequent DIC increase due to CO2 invasion,thus confirming viability of the basic concept of enhanced silicateweathering. However, our experiments also identified several importantchallenges with respect to the detailed quantification of the CO2 sequestration efficiency under field conditions, which includenonstoichiometric dissolution, potential pore water saturation inthe seabed, and the potential occurrence of secondary reactions. Beforeenhanced weathering of olivine in coastal environments can be consideredan option for realizing negative CO2 emissions for climatemitigation purposes, these aspects need further experimental assessment.

No MeSH data available.