CO2-removal News

Peer-reviewed Publications

El Gamal et al. (2025): Enhanced carbon dioxide mineralization of industrial alkaline wastes through date palm waste-derived activated biochar

Maisa El Gamal, Ameera F. Mohammad, Basim Abu-Jdayil, Suhaib Hameedi and Imen Ben Salem, IN: Journal of Environmental Management, https://doi.org/10.1016/j.jenvman.2025.127268

This study presents a sustainable approach for synthesizing activated biochar (BC) from date palm waste and enhancing its carbon dioxide (CO₂) capture capacity through integration with industrial alkaline waste, particularly ladle furnace slag (AW-LF). BC was produced via pyrolysis at 450 °C, 600 °C, and 750 °C and chemically activated using potassium carbonate (K₂CO₃) and hydrogen peroxide (H₂O₂). The materials were tested under CO₂ gas flow (10 % CO₂, 0.6 L/min, 1–2 bar, 22–25 °C) using a fluidized bed reactor.

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Peer-reviewed Publications

Haque et al. (2025): Agronomic performance of enhanced rock weathering in a tropical smallholder system: A maize trial in Kenya

Fatima Haque, Benjamin Möller, Susan Sagina, Cavince Odhiambo, Herine Ondolo, Ngugi Thuo, Kevin Kamau and Sam Davies, IN: CDRXiv, https://doi.org/10.70212/cdrxiv.2025410.v1

Enhanced Rock Weathering (ERW) is a promising negative emission technology that can simultaneously sequester atmospheric CO₂ and improve agricultural productivity. While its efficacy has been demonstrated in temperate climates, a critical knowledge gap exists regarding its application within the complex, low-input smallholder farming systems of sub-Saharan Africa. This study investigates the agronomic impacts of applying a locally sourced volcanic rock powder (nephelinite) on smallholder farms in Kisumu County, Kenya. The trial was conducted with 56 women smallholder maize farmers, with each farm divided into a control plot and a treatment plot. A single application of the rock powder (20 t/ha) was applied at the start of the trial. A significant yield benefit was sustained and amplified in the second year.

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Peer-reviewed Publications

McBride et al. (2025): Quantifying potential carbon dioxide removal via enhanced weathering using porewater from a field trial in Scotland

Amy L. McBride, Kirstine Skov, Peter Wade, Joey Betz, Amanda Stubbs, Tzara Bierowiec, et al., IN: Frontiers in Climate, https://doi.org/10.3389/fclim.2025.1606574

Enhanced weathering (EW) is cited as a promising carbon dioxide removal (CDR) strategy, and is being rapidly commercialized. Rigorous monitoring, reporting and verification (MRV) are essential to ensure carbon claims are accurate and carbon credits are not mis-sold. MRV protocols incorporate multiple approaches, including soil and porewater sampling. This paper calculates potential CDR (pCDR) from porewater (direct pCDR), via an alkalinity estimation calculated from charge balance, and from soil samples (inferred pCDR), via the accumulation of exchangeable cations on soil exchange sites. These pCDR estimations are then compared to the maximum theoretical CDR potential. The data were collected from a 1.5 year field trial, situated in south-east Scotland. Crushed basalt was surface-applied to plots at rates of 0 (control), 23, 78 and 126 t ha−1. Application rates were increased relative to common agricultural spreading practices (78 and 126 t ha−1) to increase the chances of detecting a signal. To calculate direct pCDR from porewater, ion concentrations of porewater samples extracted from a depth of 5 and 10 cm were integrated with precipitation surplus to estimate the flux of cations leaching from each depth over c. 2 week periods, as water budgets allowed. Ordinary least squares model results identified a significant effect of treatment as an explanatory variable for potential CDR, both at 5 and 10 cm depth.

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Peer-reviewed Publications

MacDonald et al. (2025): Atmospheric carbon dioxide mineralisation in anthropogenically-derived carbonate deposits

John MacDonald, Charlotte Slaymark, Amanda Stubbs and Marta Kalabová, IN: Swiss Digital Karst, https://doi.org/10.57035/journals/sdk.2025.e31.1929

Removing carbon dioxide from the atmosphere is important in minimising the impact of anthropogenically-induced climate change. Anthropogenic geomaterials, such as slag and cement, can be utilised in an engineered context for mineralising CO₂. However, such anthropogenic geomaterials, typically waste products, were usually deposited on the land surface and left to passively mineralise CO₂, resulting in the formation of anthropogenic carbonates. In this study, the authors document anthropogenic carbonates from a suite of locations across Scotland and Northern England, and use stable carbon and oxygen isotopes to show that they are formed from atmospheric CO₂.

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Peer-reviewed Publications

Alshammari et al. (2025): CO₂ Mineralization in Produced Water: Transforming Waste Brines into a Carbon Sink

Salem Alshammari, Hussain Saleem, Dong Kyu, IN: Society of Petroleum Engineers Middle East Oil & Gas Show, https://doi.org/10.2118/227029-MS

Produced brines from oil and gas fields are rich in divalent cations, offering the potential for CO₂ sequestration as thermodynamically stable carbonates. This study investigates CO₂ mineralization in produced water through yard testing the brine alkalization process in a continuously stirred tank reactor (CSTR) having a capacity of 600 L to demonstrate the kinetics and thermodynamics of magnesium and calcium hydroxide mineral precipitation at different pH regimes. Analytical characterization of the brine chemistry was done using ion chromatography (IC), inductively coupled plasma-atomic absorption spectroscopy (ICP-AES) and pH measurements. The results from the yard test demonstrate the selective removal of magnesium hydroxide after the initial alkalization step with a pH value between 8 to 9 followed by calcium hydroxide formation after the complete removal of magnesium at a pH above 10. A holistic understanding of the effect of process parameters like temperature, pressure, solid-to-liquid ratio, and the aqueous medium ionic strength is crucial for the rational design of large-scale ex-situ CO₂ mineralization processes. Therefore, the authors investigated various parameters affecting the carbonation of the extracted calcium hydroxide minerals from the alkalization process using chemical thermodynamic modeling. The models were based on Pitzer’s equations to account for the deviation from ideality in the electrolyte solution and compute the activities of its components whereas the gas phase fugacity was modeled using the Peng-Robenson (PR) equation of state. Increasing the temperature and reducing the pressure enhanced the CO₂ mineralization thermodynamic yield. They also studied the stepwise addition of CO₂ in a system of calcium hydroxide in water until a certain fugacity is reached (e.g., 1 atm). This simulates scenarios where CO₂ mass transfer or the hydration/hydroxylation of CO₂ is limiting.

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Peer-reviewed Publications

Ninfole & Rosendahl (2025): Direct Air Capture and interactions with the electricity market – Preprint

Stefano Ninfole and Knut Einar Rosendahl, IN: SSRN, https://doi.org/10.2139/ssrn.5468320

Direct Air Capture (DAC) operation is very energy intensive, and large-scale use of DAC will thus impact the electricity market. Meanwhile, electricity generation is becoming more volatile with bigger share of intermittent technologies. This paper examines possible interactions between the electricity market and adoption of DAC technologies. Combining theoretical analysis with stylized numerical simulations, the authors show that DAC adoption can increase or decrease electricity price volatility, depending on the choice of DAC technology.

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Peer-reviewed Publications

Jang et al. (2025): Influence of extreme temperature conditions on CO₂ direct air capture using amino-acid solutions

Gyoung Gug Jang, Abishek Kasturi, Jorge Gabitto, Gang Seob Jung, Pimphan Aye Meyer, Diana Stamberga, Nathan Wood, Christina Forrester, Jonathan Willocks, Radu Custelcean and Costas Tsouris, IN: Chemical Engineering Journal, https://doi.org/10.1016/j.cej.2025.168278

Many regions face challenges due to variable weather conditions including seasonal temperature fluctuations, high or low humidity, and sub-ambient temperatures. These extremes can reduce DAC performance or even lead to catastrophic events. Aqueous solvents considered for DAC systems are particularly vulnerable to seasonal variations in colder climates, where the solvent may underperform or freeze. It is therefore essential to investigate the CO₂ capture efficiency of aqueous solvents across a broad range of environmental temperatures, spanning sub-zero to hot conditions (>30 °C). In this study, DAC operation is examined using a high-flux solvent–air crossflow contactor under two major weather scenarios: (i) cold conditions below 0 °C and (ii) hot conditions above 30 °C. A parametric study is conducted to investigate the contactor performance regarding CO₂ removal efficiency, uptake capacity, and reaction kinetics versus temperature when the air velocity through the contactor exceeds 1 m/s. The efficacy of the contactor is systematically investigated using various anti-freeze amino-acid solvent formulations. A mass-transfer mechanistic model is developed to assess the process performance over a wide temperature range and propose scalable design guidelines. Machine learning is also employed to identify key parameters affecting the CO₂ capture efficiency.

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Peer-reviewed Publications

Nature – Liu et al. (2025): Hysteresis and reversibility of agroecological droughts in response to carbon dioxide removal

Laibao Liu, Mathias Hauser, Michael Windisch and Sonia I. Seneviratne, IN: Nature Water, https://doi.org/10.1038/s44221-025-00487-8

Agroecological droughts are expected to increase with climate change, becoming one of the greatest threats to ecosystems and human society. To mitigate climate change and the growing risk of agroecological droughts, carbon dioxide removal (CDR) is increasingly recognized as unavoidable. However, it remains unclear whether the increase of agroecological drought due to atmospheric CO₂ emissions will be symmetrically reversed by an equivalent atmospheric CDR. Here the authors investigate this question by utilizing an idealized atmospheric CO₂ emission and removal experiment from the CDR Model Intercomparison Project, involving eight Earth system models, and develop a new methodology to quantify climate hysteresis and reversibility.

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Peer-reviewed Publications

Kukla et al. (2025): Swapping carbonate for silicate in agricultural enhanced rock weathering

Tyler Kukla, Yoshiki Kanzaki, Freya Chay, Noah Planavsky, Chris Reinhard, IN: CDRXiv, https://doi.org/10.70212/cdrxiv.2025304.v1

Enhanced rock weathering with crushed silicates is often considered as an alternative to agricultural liming for soil pH management and carbon dioxide removal. But swapping carbonates for silicates does not guarantee better carbon removal outcomes. Carbonates weather rapidly, and recent work has found that they can remove more carbon than fast-reacting silicates in some environments. On the other hand, carbonate dissolution can mobilize fossil carbon and potentially lead to carbon emissions, depending on the spatial and temporal boundaries of the system. Here, the authors use a one-dimensional reactive transport model, SCEPTER, to analyze the conditions where carbonate weathering breaks even with basalt — a common silicate rock used in enhanced weathering — from an end-to-end carbon removal perspective.

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Peer-reviewed Publications

Roesch et al. (2025): Life cycle assessment of different biochar application scenarios in Swiss agriculture

Andreas Roesch, Nadège Vaucher, Antonia Mantonanaki, Martin Stüssi, Jens Lansche and Nikolas Hagemann, IN: Agroscope Report, https://doi.org/10.34776/as210e

The main objective of this study was to analyse the climate change impact of biochar production and application across the entire Swiss agricultural value chain quantified by the 100-year time horizon global warming potential (GWP100), hereinafter referred to as GWP for simplicity, using life cycle assessment (LCA). In Switzerland, biochar is often not applied directly to the soil; instead, it is used in animal husbandry (feed additive, animal bedding),
so that it enters the soil as part of the manure. Given the potential effects of biochar at various levels beyond its application (e.g. in animals, on the air quality in the stable, in the manure, etc.), this is also referred to as cascade use.

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