The influence of particle size on the potential of enhanced basalt weathering for carbon dioxide removal – Insights from a regional assessment

Enhanced weathering through basalt application on agricultural land represents a proposed strategy for the removal of carbon dioxide from the atmosphere. It has been shown that enhanced weathering is principally feasible on a global scale, but there is still uncertainty with respect to the predicted drawdown in a given timeframe. This information is however vital to evaluate, if enhanced weathering should be further considered as a factor to alleviate the impact of the climate crisis. With this in mind, this article reviews of the current state of research and estimates the CO2 drawdown for scenarios using basalt powders of different particle size distribution (<100 μm, <10 μm and <1 μm). Calculated with a modified shrinking core model, the amount of powder dissolved within a timeframe of 10 years is approximately 16% (<100 μm), 55% (<10 μm) and 99.9% (<1 μm). This corresponds to a gross CO2 removal of 0.045 t CO2 t−1 of rock (<100 μm) and 0.153 t CO2 t−1 of rock, (<10 μm). We evaluate our results on regional scale through a case study for Austria, including emissions from mining, comminution, application and transport. Assuming an average distance of 300 km from mine to field, the net CO2 drawdown decreases to approximately 0.027 t CO2 t−1 of rock (<100 μm) or 0.096 t CO2 t−1 (<10 μm), when rail transport is used. For truck transport, the numbers are reduced to −0.030 t CO2 t−1 of rock (<100 μm) or 0.039 t CO2 t−1 (<10 μm), respectively. Accordingly, at the current CO2 intensity, transport related emissions may cancel out any drawdown if grain sizes (<100 μm) are used. Our estimates suggest that enhanced weathering will only significantly contribute to net CO2 drawdown if grain sizes (<10 μm) are used. Under these conditions the large-scale application of particles with a diameter <10 μm may remove about 2% of Austria's annual Greenhouse gas emissions. We discuss challenges towards this goal, including the enormous amounts of rock needed and the energy requirement related to grinding, as well as uncertainties related to actual field weathering rates. Those uncertainties hinder the precise quantification of CO2 drawdown as of now. While enhanced weathering remains a promising path for climate change mitigation, further research at laboratory and field scale is required to put this technology to optimal use. Download

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