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

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.


(A) SEM–EDX micrograph of unreacted olivine (substrate material)with very clear angular features and sharp edges. The Mg-to-Si atomicratio in area 1 typically lies between 2 and 2.5. (B) SEM–EDXmicrograph of an olivine particle after being subjected to continuousmovement in FSW during 137 days (experiment A3). On the surface ofthe same olivine particle, abrupt changes in Mg-to-Si atomic ratioscan be observed within small distances. Areas denoted with 1 are characterizedby Mg-to-Si atomic ratios of 2–2.5, while Mg-to-Si atomic ratiosin areas denoted with 2 showed values of around 1. Such locations,where the Mg-to-Si ratio decreases well below 2, are considered localweathering sites.
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fig4: (A) SEM–EDX micrograph of unreacted olivine (substrate material)with very clear angular features and sharp edges. The Mg-to-Si atomicratio in area 1 typically lies between 2 and 2.5. (B) SEM–EDXmicrograph of an olivine particle after being subjected to continuousmovement in FSW during 137 days (experiment A3). On the surface ofthe same olivine particle, abrupt changes in Mg-to-Si atomic ratioscan be observed within small distances. Areas denoted with 1 are characterizedby Mg-to-Si atomic ratios of 2–2.5, while Mg-to-Si atomic ratiosin areas denoted with 2 showed values of around 1. Such locations,where the Mg-to-Si ratio decreases well below 2, are considered localweathering sites.

Mentions: SEM–EDX analyses of mineral grainsfrom fresh, unreacted olivine were generally angular, with sharp edges(Figure 4A). In contrast,olivine grains that had been rotating during the entire experiment(137 days) were generally subrounded (Figure 4B), suggesting abrasion due to grain–graincollisions. The Mg-to-Si atomic ratios (Mg/Si) at the surface of theunreacted particles were significantly higher (mean ± SEM Mg/Si= 2.11 ± 0.02, ngrains = 6; Figure S9) than for grains that were agitatedin solution (mean ± SEM Mg/Si 1.7 ± 0.04–2 ±0.03, ngrains = 3–10; Figure S9). This suggests preferential mobilizationof Mg during dissolution, consistent with the higher dissolution ratesobtained for Mg and Ni compared to Si. The preferential leaching ofMg2+ (lowest Mg-to-Si ratio) was most prominent in theASW-CaMg treatment (Figure S10), whereareas with Mg/Si ≤ 1 and lower were observed. No carbonateminerals were observed on any of the analyzed olivine grains.


Olivine Dissolution in Seawater: Implications forCO 2 Sequestration through Enhanced Weathering in CoastalEnvironments
(A) SEM–EDX micrograph of unreacted olivine (substrate material)with very clear angular features and sharp edges. The Mg-to-Si atomicratio in area 1 typically lies between 2 and 2.5. (B) SEM–EDXmicrograph of an olivine particle after being subjected to continuousmovement in FSW during 137 days (experiment A3). On the surface ofthe same olivine particle, abrupt changes in Mg-to-Si atomic ratioscan be observed within small distances. Areas denoted with 1 are characterizedby Mg-to-Si atomic ratios of 2–2.5, while Mg-to-Si atomic ratiosin areas denoted with 2 showed values of around 1. Such locations,where the Mg-to-Si ratio decreases well below 2, are considered localweathering sites.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: (A) SEM–EDX micrograph of unreacted olivine (substrate material)with very clear angular features and sharp edges. The Mg-to-Si atomicratio in area 1 typically lies between 2 and 2.5. (B) SEM–EDXmicrograph of an olivine particle after being subjected to continuousmovement in FSW during 137 days (experiment A3). On the surface ofthe same olivine particle, abrupt changes in Mg-to-Si atomic ratioscan be observed within small distances. Areas denoted with 1 are characterizedby Mg-to-Si atomic ratios of 2–2.5, while Mg-to-Si atomic ratiosin areas denoted with 2 showed values of around 1. Such locations,where the Mg-to-Si ratio decreases well below 2, are considered localweathering sites.
Mentions: SEM–EDX analyses of mineral grainsfrom fresh, unreacted olivine were generally angular, with sharp edges(Figure 4A). In contrast,olivine grains that had been rotating during the entire experiment(137 days) were generally subrounded (Figure 4B), suggesting abrasion due to grain–graincollisions. The Mg-to-Si atomic ratios (Mg/Si) at the surface of theunreacted particles were significantly higher (mean ± SEM Mg/Si= 2.11 ± 0.02, ngrains = 6; Figure S9) than for grains that were agitatedin solution (mean ± SEM Mg/Si 1.7 ± 0.04–2 ±0.03, ngrains = 3–10; Figure S9). This suggests preferential mobilizationof Mg during dissolution, consistent with the higher dissolution ratesobtained for Mg and Ni compared to Si. The preferential leaching ofMg2+ (lowest Mg-to-Si ratio) was most prominent in theASW-CaMg treatment (Figure S10), whereareas with Mg/Si ≤ 1 and lower were observed. No carbonateminerals were observed on any of the analyzed olivine grains.

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.