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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.


Related in: MedlinePlus

Olivine dissolution rate constant k, calculatedas the mean (± SD) value of the different response variablesmeasured in the three agitation experiments A1, A2, and A3 (Table S4). To obtain the most-realistic estimatesfor olivine dissolution in seawater, only values from the FSW andASW treatments were considered. For comparison, the estimated valueby Hangx and Spiers14 from previous studies(literature, H&S 2009) is given in the same units as the ratesobtained in this study. The literature value and range are denotedby the gray circle and the gray area for clarity. The gray trianglesrepresent the values obtained in this study at 17 °C but recalculatedto 25 °C, the same standard temperature as the literature estimates.
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fig3: Olivine dissolution rate constant k, calculatedas the mean (± SD) value of the different response variablesmeasured in the three agitation experiments A1, A2, and A3 (Table S4). To obtain the most-realistic estimatesfor olivine dissolution in seawater, only values from the FSW andASW treatments were considered. For comparison, the estimated valueby Hangx and Spiers14 from previous studies(literature, H&S 2009) is given in the same units as the ratesobtained in this study. The literature value and range are denotedby the gray circle and the gray area for clarity. The gray trianglesrepresent the values obtained in this study at 17 °C but recalculatedto 25 °C, the same standard temperature as the literature estimates.

Mentions: Because of nonstoichiometric dissolution, the olivine dissolutionrate constant ki showed a dependence onthe response variable (ΔSi, ΔNi, ΔMg, ΔTA,and ΔDIC; Table 2). The rate constant based on ΔNi (kΔNi) is the highest of all response variables and is similar acrossall treatments (31–74 μmol of olivine m–2 day–1). In the ASW-CaMg treatment, kΔMg (63 μmol of olivine m–2 day–1) was consistent with kΔNi values, while kΔSi were an order of magnitude lower than kΔNi values in the reactive fluid media containing Mg2+ (Table 1 and 2). The exclusion of Mg2+ in the Mg-free reactivefluid (ASW-CaMg) increased kΔSi by1 order of magnitude. The values of both kΔTA and kΔDIC showsubstantial variation between treatments, and are highest in the ASW-CaMgtreatment. The temperature-normalized24 (to 25 °C) mean values for ki (wherei = ΔSi, ΔNi, ΔTA, or ΔDIC), for the FSW andASW cases are shown in Figure 3 (the ASW-Ca and ASW-CaMg treatments are considered unrealisticfor ESW and are thus excluded).


Olivine Dissolution in Seawater: Implications forCO 2 Sequestration through Enhanced Weathering in CoastalEnvironments
Olivine dissolution rate constant k, calculatedas the mean (± SD) value of the different response variablesmeasured in the three agitation experiments A1, A2, and A3 (Table S4). To obtain the most-realistic estimatesfor olivine dissolution in seawater, only values from the FSW andASW treatments were considered. For comparison, the estimated valueby Hangx and Spiers14 from previous studies(literature, H&S 2009) is given in the same units as the ratesobtained in this study. The literature value and range are denotedby the gray circle and the gray area for clarity. The gray trianglesrepresent the values obtained in this study at 17 °C but recalculatedto 25 °C, the same standard temperature as the literature estimates.
© Copyright Policy
Related In: Results  -  Collection

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

fig3: Olivine dissolution rate constant k, calculatedas the mean (± SD) value of the different response variablesmeasured in the three agitation experiments A1, A2, and A3 (Table S4). To obtain the most-realistic estimatesfor olivine dissolution in seawater, only values from the FSW andASW treatments were considered. For comparison, the estimated valueby Hangx and Spiers14 from previous studies(literature, H&S 2009) is given in the same units as the ratesobtained in this study. The literature value and range are denotedby the gray circle and the gray area for clarity. The gray trianglesrepresent the values obtained in this study at 17 °C but recalculatedto 25 °C, the same standard temperature as the literature estimates.
Mentions: Because of nonstoichiometric dissolution, the olivine dissolutionrate constant ki showed a dependence onthe response variable (ΔSi, ΔNi, ΔMg, ΔTA,and ΔDIC; Table 2). The rate constant based on ΔNi (kΔNi) is the highest of all response variables and is similar acrossall treatments (31–74 μmol of olivine m–2 day–1). In the ASW-CaMg treatment, kΔMg (63 μmol of olivine m–2 day–1) was consistent with kΔNi values, while kΔSi were an order of magnitude lower than kΔNi values in the reactive fluid media containing Mg2+ (Table 1 and 2). The exclusion of Mg2+ in the Mg-free reactivefluid (ASW-CaMg) increased kΔSi by1 order of magnitude. The values of both kΔTA and kΔDIC showsubstantial variation between treatments, and are highest in the ASW-CaMgtreatment. The temperature-normalized24 (to 25 °C) mean values for ki (wherei = ΔSi, ΔNi, ΔTA, or ΔDIC), for the FSW andASW cases are shown in Figure 3 (the ASW-Ca and ASW-CaMg treatments are considered unrealisticfor ESW and are thus excluded).

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.


Related in: MedlinePlus