ORIGINAL RESEARCH article
Front. Clim.
Sec. Carbon Dioxide Removal
Evidence for carbon dioxide removal via enhanced rock weathering with steel slag, though not basalt, in a midwestern U.S. field trial
Provisionally accepted
Daniel P. Maxbauer1*
Ella Milliken2
Jahmaine Renzo Yambing3,4Emma Watson1Rachel B Gregg1
Liza Swanson1
Jaeeun Sohng5
Noah W Sokol6Noah J Planavsky2- 1Carleton College, Northfield, United States
- 2Yale University Department of Earth & Planetary Sciences, New Haven, United States
- 3Massachusetts Institute of Technology, Cambridge, United States
- 4Woods Hole Oceanographic Institution, Woods Hole, United States
- 5University of California Davis John Muir Institute of the Environment, Davis, United States
- 6Lawrence Livermore National Laboratory Physical and Life Sciences Directorate, Livermore, United States
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Enhanced weathering is an emergent pathway for permanent atmospheric carbon dioxide removal (CDR). However, despite a dramatic increase in academic and commercial research, there remain relatively few published examples of field evidence demonstrating the effectiveness of enhanced weathering. Here, we present results from a three-year field trial that evaluated steel slag and crushed basalt applied as amendments in a conventional agricultural system in the Midwestern United States. Steel slag applied to initially acidic soil increased porewater pH and alkalinity and increased soil pH and Ca-saturation. Together, changes in porewater chemistry and soil properties provide strong evidence for steel slag weathering and CDR. However, steel slag applied to soils with a neutral initial pH did not generate significant changes in soil or porewater chemistry. In addition, coarse-grained crushed basalt did not generate detectable signals for carbonic acid weathering in any of the soils. The impact of strong acids on mineral weathering was apparent in all three years of monitoring soil porewater chemistry. Overall, our results demonstrate clear evidence of CDR from applying steel slag amendments to acidic cropland soils while also highlighting the difficulty of greenhouse gas reduction accounting from enhanced weathering and the variable outcomes that can occur depending on feedstock and soil type.
Keywords: enhanced weathering, Carbon dioxide removal, basalt, Steel slag, Soilcarbon
Received: 30 Jun 2025; Accepted: 17 Nov 2025.
Copyright: © 2025 Maxbauer, Milliken, Yambing, Watson, Gregg, Swanson, Sohng, Sokol and Planavsky. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Daniel P. Maxbauer, dmaxbauer@carleton.edu
Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.