Sequestering carbon through carbon mineralization
Carbon mineralization occurs naturally on Earth’s surface, when rocks enriched with magnesium and calcium (known as ultramafics) are exposed to water that is rich with CO2, causing the CO2 to bind to the rocks as a solid mineral. LLNL scientists aim is to determine whether this process can take place at a sufficient scale to remove atmospheric CO2 and permanently sequester it on Earth’s surface or underground.
Research teams at LLNL—and their academic collaborators—are tapping into experimental capabilities offered at CAMS to determine how much of the CO2 sequestered through carbon mineralization is “new” CO2, pulled recently from the atmosphere, and how much has been on Earth’s surface for a long time. They collect samples from recently exposed ultramafic rock surfaces, such as landslides and waste material from mines, and then analyze the samples at CAMS, measuring the age of the sequestered CO2. Findings indicate that nearly all of the carbon in the carbonates came from the atmosphere, providing confidence that carbon mineralization can play a key role in future large-scale carbon sequestration.
Key collaborator: University of British Columbia
What’s next: LLNL scientists are exploring:
- The types of rocks that are a natural fit for mineralization (e.g., crushed rocks with a large surface area, or rocks that release a large quantity of magnesium and calcium), and conditions that could accelerate the mineralization process.
- Materials in Earth’s subsurface that may also be good candidates for long-term carbon sequestration via mineralization.
- The potential for enhanced weathering of surface-applied rock dust for sequestering atmospheric CO2.
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Land management for enhanced carbon storage
LLNL scientists, along with multiple external collaborators, are exploring options for boosting carbon sequestration in agricultural soil. Their research includes studies of crop management and conversion from annual to perennial plants. Early work in this area focused on studying the effects of deeply rooted perennial plants, such as switchgrass (a native prairie grass), on soil organic carbon.
In addition, LLNL scientists are participating in the DOE-funded Center for Advanced Bioenergy and Bioproducts Innovation (CABBI) project. The aim of this research is to understand the plant, soil, microbe, and other ecosystem interactions that underlie the productivity of different ecosystems. As part of these efforts, scientists are leveraging experimental capabilities offered at CAMS to conduct isotope-based characterization of soil samples collected at the University of Illinois’s Energy Farm. This analysis enables them to quantify soil carbon accrual in agricultural and grassland soils, and track the fate of newly sequestered carbon into long-lived soil carbon pools.
Key collaborators:
- LLNL is collaborating with two national laboratories and 10 universities as part of the Terraforming Soil Energy Earthshot Research Center.
- LLNL is collaborating in the CABBI project with the University of Illinois Urbana‒Champaign, which leads the project, along with 19 other partnering institutions.
What’s next: In addition to studying agricultural land management, LLNL scientists are investigating the carbon impact of various bioenergy crops, as well as the impact of replacing annual plants with deeper rooted perennials. An experimental carbon garden in LLNL’s open campus will allow study of CO2 sequestration potential of perennial grasses that are native to California.
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Developing a new analytical capability: Compound-specific radiocarbon analysis
LLNL scientists continue enhancing research capabilities as they tackle new challenges. For example, they recognized that they needed to obtain more detailed data when analyzing soils samples to study the environmental parameters that affect carbon cycles. In response, they developed a new sample preparation technique that provides them with more detailed data when analyzing soil samples using the CAMS accelerators.
With traditional sample preparation techniques, scientists can obtain data regarding the average amount of time that all organic compounds have been present in a soil sample. However, with the new techniques being developed at LLNL, scientists can obtain compound-specific radiocarbon information. They can measure the age of each type of carbon (e.g., each specific molecular class of organic matter) in the soil sample.
By knowing how long each compound has been present in a terrestrial reservoir, they gain insight regarding how vulnerable the reservoir is to environmental changes. For example, they can identify the rate at which specific compounds cycle through an ecosystem, and which type of carbon is most vulnerable to loss following disturbance or other environmental changes.
To develop the new technique, researchers started by adapting an existing technique used to measure samples from marine ecosystems, modifying it for use with samples obtained from terrestrial ecosystems. Soils contain a lot of material that is not carbon (e.g., minerals), and the new sample preparation technique enables researchers to separate the carbon in a soil sample into individual organic compounds, prior to analysis. Compound classes can be further separated into increasingly specific biomarkers that can be linked to specific plant and microbial sources, which are indicators of fire history, or are concerns for environmental quality (e.g., chemical pollutants or algal blooms).
What’s next: The research team’s initial work using the new technique involved samples collected from grassland ecosystems. The next step is to modify the technique so it can be used with new classes of compounds, collected from other types of ecosystems. As they leverage these additional analytical capabilities for other ecosystems, they hope to gain insight regarding how rapidly plant material decomposes in the ecosystem, how soil carbon molecules are transformed by soil microbes, and which type of carbon persists in the terrestrial reservoir.
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