Higher Inorganic CO₂ Removal Despite Slower Weathering in an Enhanced Weathering Experiment With Steel Slags and...

Area of Science:

• Earth and Environmental Sciences
• Climate Change Mitigation
• Geochemistry

Background:

• Silicate weathering inspires CO2 removal technologies: enhanced weathering and mineral carbonation.
• Combining these methods aims to maximize carbon dioxide sequestration.
• Understanding inorganic CO2 removal efficiencies is crucial for climate solutions.

Purpose of the Study:

• To investigate the combined effects of enhanced weathering and mineral carbonation on CO2 removal.
• To assess the impact of pre-carbonated steel slags on soil carbon pools.
• To determine the factors limiting inorganic CO2 removal efficiency.

Main Methods:

• A 15-month mesocosm experiment using maize-planted soil.
• Application of pre-carbonated and uncarbonated steel slags (BOF, AOD) and basalt.
• Analysis of various soil pools (leachate, carbonate, plant, exchangeable, (hydr)oxide, SOM) beyond traditional assessments.

Main Results:

• Inorganic CO2 removal remained low (<0.014 t CO2/t rock) across most treatments.
• The highest carbonated slag treatment showed increased CO2 removal (0.04 t CO2/t rock).
• Rapid slag weathering led to secondary mineral formation, immobilizing base cations and limiting CO2 removal (<5.3% theoretical potential).

Conclusions:

• High prior mineral carbonation can enhance CO2 removal during enhanced weathering, even with slower weathering rates.
• Rapid weathering and secondary mineral precipitation constrain inorganic CO2 removal efficiency.
• Assessing the fate of weathering products in all soil pools is essential for accurate CO2 removal potential evaluation.