This week’s publication highlights relate to a wide range of CDR methods such as direct air capture, enhanced rock weathering and forestation.
Pyrogenic Carbon and Carbonating Minerals for Carbon Capture and Storage (PyMICCS) part II: Organic and Inorganic Carbon Dioxide Removal in an Oxisol
Abstract
Enhanced rock weathering (ERW) and pyrogenic carbon capture and storage (PyCCS, or “biochar carbon removal”) are two promising carbon dioxide removal (CDR) techniques that can contribute to soil restoration. These technologies can be combined by co-application of rock powder and biochar or by co-pyrolysis of rock powder with biomass to produce rock-enhanced (RE) biochar. In a 27-week laboratory experiment, we quantified the carbon (C) sink development of co-applications and RE-biochars produced by co-pyrolysis of basanite rock powder with either 50 or 90 wt% willow wood or 90 wt% wheat straw. Incubators featured two elevated soil pCO2 levels (0.012 and 0.062 atm, equivalent to about 1.2 and 6.2 Vol-% CO2) in a clay-rich, nutrient-poor Oxisol, with a simulated annual rainfall of 1,600 mm. Results showed strong initial fluxes of total alkalinity (TA), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and major cations (Mg2+, Ca2+, K+, Na+), which decreased over time. Notably, elevated pCO2 had minimal impact on the release of DOC but doubled the TA flux from ERW. An important observation was the impact of waterlogging on water fluxes in soil columns without biochar, which lowered the amount of leached cations from rock and biochar. We defined the carbon sink (C-Sink) to include all DIC of geogenic and biogenic origin, and pyrogenic carbon from biochar. Biogenic cations were not considered as contributing to additional CO2 sequestration. For a soil application equivalent to application of 12 t ha−1, the total net C-Sink ranged from −0.1 to 30.9 t CO2 ha−1 after 27 weeks under 1.2 Vol-% CO2. We were not able to determine a change in rock weathering rates from co-pyrolysis since biogenic and geogenic cations could not be distinguished. A 20-year forecast suggests net C-Sinks between 0.5 t and 28.7 t CO2 ha−1, driven by increased contributions from weathering, alongside a C-Sink loss of carbon due to biochar mineralization. While biochar alone generally produces a larger C-Sink, co-application with rock powder fosters soil remineralization and provides a higher permanence of the C-Sink. Additionally, biochar increases water-holding capacity, prevents waterlogging of soils and likely improves the retention of organic carbon in soils.
Vorrath, M. et al. (2025) Pyrogenic Carbon and Carbonating Minerals for Carbon Capture and Storage (PyMICCS) part II: Organic and Inorganic Carbon Dioxide Removal in an Oxisol 7 (1592454) Frontiers in Climate.
Read the full article here: Pyrogenic Carbon and Carbonating Minerals for Carbon Capture and Storage (PyMICCS) part II: Organic and Inorganic Carbon Dioxide Removal in an Oxisol I Frontiers in Climate.
Comparative Analysis of Amine-Functionalized Silica for Direct Air Capture (DAC): Material Characterization, Performance, and Thermodynamic Efficiency
Abstract
Direct air capture (DAC) technology faces challenges due to energy-intensive processes and limited CO2 capture capacity under atmospheric concentration. Utilizing adsorption techniques with solid sorbents offers a sustainable solution. This study investigates the performance, efficiency, and regeneration energy of various amines (TEPA, low and high molecular weights PEI and APTES) functionalized mesoporous silica (SBA-15) for DAC. Comprehensive investigations, including characterization and thermodynamic efficiency evaluation, are conducted for CO2 adsorption under dry and humid conditions (50 % RH). Functionalizing SBA-15 with TEPA, PEI-L and PEI-H, and TEPA significantly improves CO2 adsorption, increasing capacities to 2.1, 1.36, and 1.11 mmol/g, respectively, and introduction of humidity further increases CO2 capacities to 3.17, 2.87, and 1.68 mmol/g, respectively. However, there’s a trade-off in thermodynamic efficiency due to energy consumed in desorbing water molecules. S-TEP exhibits the highest thermodynamic efficiency in dry conditions, while S-PEI-L achieves the highest efficiency in humid conditions. Stability tests of all material in addition to, the commercial material, lewatit demonstrate robust regenerability over 10 cycles under both dry and humid conditions (50 % RH). This study provides insights into functionalized SBA-15 performance in CO2 adsorption, with implications for efficient and sustainable indoor DAC processes.
Surkatti, R. et al. (2025) Comparative Analysis of Amine-Functionalized Silica for Direct Air Capture (DAC): Material Characterization, Performance, and Thermodynamic Efficiency 354 (1) Separation and Purification Technology.
Read the full paper here: Comparative Analysis of Amine-Functionalized Silica for Direct Air Capture (DAC): Material Characterization, Performance, and Thermodynamic Efficiency I Separation and Purification Technology.
Enhanced Rock Weathering Altered Soil Organic Carbon Fluxes in a Plant Trial
Abstract
Enhanced rock weathering (EW) is gaining attention as a promising carbon dioxide removal strategy, primarily due to its potential to sequester inorganic carbon through mineral dissolution. However, the broader biogeochemical implications of EW, particularly its effects on soil organic carbon (SOC) dynamics, as well as the role played by agriculturally relevant biota such as plants and earthworms, remain poorly understood. In a 15-month mesocosm experiment with Zea mays, we investigated how EW with basalt influences soil CO2 efflux (SCE; normalized for soil water content and temperature) and how this is modulated by plant and earthworm presence. Using δ13C-CO2 isotope tracing based on the C3–C4 shift method, we partitioned normalized SCE into rhizosphere (root plus microbial respiration of rhizodeposits) and soil organic matter components. In the first growing season, basalt increased normalized SCE 2.8-fold in planted mesocosms relative to planted controls, due to elevated rhizosphere respiration. In contrast, during the second growing season, basalt significantly decreased normalized SCE 16.5-fold, but only in unplanted mesocosms. Mediation analysis revealed that basalt also indirectly influenced SCE via changes in soil water content, with the direction of this effect depending on plant presence and growing season. Basalt showed contrasting direct and indirect effects, highlighting the complexity of soil responses to silicate amendments, where multiple, sometimes opposing, processes operate simultaneously. Disentangling such effects is essential for understanding the impact of EW on soil carbon and for effective and reliable upscaling. Our findings suggest that SOM stabilization might occur after basalt application, decreasing SCE. Moreover, they demonstrate that both biotic and abiotic factors (e.g., vegetation, soil fauna, soil moisture) can modulate the impact of EW on SOC dynamics. To quantify the climate change mitigation effect of EW, research must move beyond inorganic carbon and explicitly integrate biotic and organic processes into EW assessments.
Boito, L. et al. (2025) Enhanced Rock Weathering Altered Soil Organic Carbon Fluxes in a Plant Trial 31 (8) Global Change Biology.
Read the full article here: Enhanced Rock Weathering Altered Soil Organic Carbon Fluxes in a Plant Trial I Global Change Biology.
Land Availability and Policy Commitments Limit Global Climate Mitigation form Forestation
Abstract
Forestation (afforestation and reforestation) could mitigate climate change by sequestering carbon within biomass and soils. However, global mitigation from forestation remains uncertain owing to varying estimates of carbon sequestration rates (notably in soil) and land availability. In this study, we developed global maps of soil carbon change that reveal carbon gains and losses with forestation, primarily in the topsoil. Constraining land availability to avoid unintended albedo-induced warming and safeguard water and biodiversity (389 million hectares available for forestation globally) would sequester 39.9 petagrams of carbon by 2050, substantially below previous estimates. This estimate drops to 12.5 petagrams of carbon with land further limited to existing policy commitments (120 million hectares). Achieving greater mitigation requires expanding dedicated forestation areas and strengthening commitments from nations with considerable but untapped potential.
Wang, Y. et al. (2025) Land Availability and Policy Commitments Limit Global Climate Mitigation from Forestation 389 (6763) Science.
Read the full paper here: Land Availability and Policy Commitments Limit Global Climate Mitigation from Forestation I Science.
Carbon Dioxide Reduction and Removal toward Net-Zero: A Needed Change of Narrative
Abstract
This work provides a simple physical framework to analyze the challenges related to achieving a net-zero carbon dioxide (CO2) emission target, with a specific focus on CO2 management solutions based on CO2 capture and storage (CCS), biomass use with CCS, and direct air capture of CO2 from the atmosphere with permanent storage. The framework is based on a simplified schematic of the Earth system, a simple mathematical model of such a system, and a graphical representation of it (called a scenario diagram), where the states of the Earth system can be mapped, from the net-positive world of today to any net-zero and net-negative future scenario. Based on this framework, our analysis demonstrates that (i) from a climate impact perspective, CO2 reduction and removal are equivalent in a net-positive world, though CO2 removal will be needed to achieve a net-zero and possibly a net-negative world; (ii) achieving net-zero emissions will eventually depend on developing enough CO2 storage volumes and decarbonizing our economy adequately; (iii) decarbonization can only happen by ultimately replacing fossil fuels in the energy and industry sectors and eliminating their use entirely. We believe that the use of the tools we have developed and the interpretation of the results we have presented can contribute to designing better incentives, optimizing resource allocation, building public trust, garnering greater support from policymakers, and ultimately leading to more effective and efficient climate policies and measures.
Kloesel, K. et al. (2025) Carbon Dioxide Reduction and Removal toward Net-Zero: A Needed Change of Narrative 64 (31) Industrial & Chemical Engineering Research.
Read the full paper here: Carbon Dioxide Reduction and Removal toward Net-Zero: A Needed Change of Narrative I Industrial & Chemical Engineering Research.