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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.


Temporal development of olivine dissolution response variablesin experiments A1 and A2. Symbols denote mean seawater-corrected values(see the Materials and Methods section), witherror bars denoting standard error of the mean (SEM). Circles: valuesfrom experiment A1; triangles: values from experiment A2. The valuesfor both experiments are plotted with the olivine (OLI) and quartz(QUA) treatments plotted alongside on the same vertical scale forcomparison. The reported units are μmol/kg of seawater, exceptfor pH, which is in pH units on the total scale.
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fig1: Temporal development of olivine dissolution response variablesin experiments A1 and A2. Symbols denote mean seawater-corrected values(see the Materials and Methods section), witherror bars denoting standard error of the mean (SEM). Circles: valuesfrom experiment A1; triangles: values from experiment A2. The valuesfor both experiments are plotted with the olivine (OLI) and quartz(QUA) treatments plotted alongside on the same vertical scale forcomparison. The reported units are μmol/kg of seawater, exceptfor pH, which is in pH units on the total scale.

Mentions: In the A1 and A2 experiments, we investigated the dissolution ofolivine and quartz in natural filtered seawater. In both A1 and A2,there was a clear ΔSi signal in the quartz treatment (QUA),most likely caused by dissolution of very fine quartz particles (Figure 1). ΔSi increaseduntil ∼18 μmol kg–1 within the firstweek of the experiments, after which it remained constant. There wasno discernible Ni release in the A1 and A2 quartz treatment (Figure 1), and hardly anyresponse from the carbonate system. The ΔpH increased by 0.05within the first 2 weeks but then decreased again to its initial valueby the end of the experiment. While ΔTA remained constant withtime, ΔDIC decreased with 22 μmol kg–1 during the first 15 days, likely caused by CO2 outgassing,as the initial solution in A1 may not have been in equilibrium withthe atmosphere (sections 2 and 3 of the Supporting Information). In the A2 experiment, the experimental procedurewas improved, and the FSW medium was bubbled with ambient air at thestart of the experiment. As a result, the carbonate system variablesΔDIC, ΔTA, or ΔpH did not change significantly overtime (linear regression, p = 0.35, p = 0.28, and p = 0.696, respectively).


Olivine Dissolution in Seawater: Implications forCO 2 Sequestration through Enhanced Weathering in CoastalEnvironments
Temporal development of olivine dissolution response variablesin experiments A1 and A2. Symbols denote mean seawater-corrected values(see the Materials and Methods section), witherror bars denoting standard error of the mean (SEM). Circles: valuesfrom experiment A1; triangles: values from experiment A2. The valuesfor both experiments are plotted with the olivine (OLI) and quartz(QUA) treatments plotted alongside on the same vertical scale forcomparison. The reported units are μmol/kg of seawater, exceptfor pH, which is in pH units on the total scale.
© Copyright Policy
Related In: Results  -  Collection

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

fig1: Temporal development of olivine dissolution response variablesin experiments A1 and A2. Symbols denote mean seawater-corrected values(see the Materials and Methods section), witherror bars denoting standard error of the mean (SEM). Circles: valuesfrom experiment A1; triangles: values from experiment A2. The valuesfor both experiments are plotted with the olivine (OLI) and quartz(QUA) treatments plotted alongside on the same vertical scale forcomparison. The reported units are μmol/kg of seawater, exceptfor pH, which is in pH units on the total scale.
Mentions: In the A1 and A2 experiments, we investigated the dissolution ofolivine and quartz in natural filtered seawater. In both A1 and A2,there was a clear ΔSi signal in the quartz treatment (QUA),most likely caused by dissolution of very fine quartz particles (Figure 1). ΔSi increaseduntil ∼18 μmol kg–1 within the firstweek of the experiments, after which it remained constant. There wasno discernible Ni release in the A1 and A2 quartz treatment (Figure 1), and hardly anyresponse from the carbonate system. The ΔpH increased by 0.05within the first 2 weeks but then decreased again to its initial valueby the end of the experiment. While ΔTA remained constant withtime, ΔDIC decreased with 22 μmol kg–1 during the first 15 days, likely caused by CO2 outgassing,as the initial solution in A1 may not have been in equilibrium withthe atmosphere (sections 2 and 3 of the Supporting Information). In the A2 experiment, the experimental procedurewas improved, and the FSW medium was bubbled with ambient air at thestart of the experiment. As a result, the carbonate system variablesΔDIC, ΔTA, or ΔpH did not change significantly overtime (linear regression, p = 0.35, p = 0.28, and p = 0.696, respectively).

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.