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Enhanced rock weathering (ERW) is a recognized carbon dioxide removal (CDR) strategy that uses crushed silicate rock (e.g., basalt) to capture atmospheric CO2, offering co-benefits such as improved soil health and increased crop production [1]. One of the main disadvantages of ERW includes the production of energy needed to crush and transport rocks to their application site [2]. Basalt quarries, which are abundant throughout the United Kingdom (UK), might be capable of removing CO2 on-site by optimizing the management of their quarry fines. This approach would reduce transport-related emissions while repurposing valuable, previously underutilized material. Basalt and dolerite fines from Breedon’s Orrock Quarry and Tarmac’s Cairneyhill Quarry in Scotland are tested in this study as potential feedstocks for ERW, respectively. These samples show evidence of on-site weathering as secondary minerals are present in some areas of the fines. Thermogravimetric analysis (TGA) on these samples corroborates field observations as 1.02% and 2.22% CO2 were detected at Orrock and Cairneyhill, respectively. It is estimated that 10 kg CO2/ t Orrock fines and 25 kg CO2/ t Cairneyhill fines have been sequestered passively. Based on the CaO and MgO content, the carbonation potential is 190 kg CO2/ t Orrock fines and 160 kg CO2/ t Cairneyhill fines. Due to the challenge of accessing this potential under ambient conditions, it's essential to evaluate various on-site basalt management practices. To test this, ex-situ, column-based experiments were performed in the following manner. Fines from both sites were placed into columns with varying thicknesses (1 cm and 5 cm) and grain sizes (bulk and <75 μm). These columns were then subjected to ambient UK conditions (10 °C, 0.04% CO2) in an environmental chamber and intensified carbonation conditions (50 °C, 20% CO2) in a CO2 incubator. Both sets of experiments have been in place for three months, with monthly water addition to facilitate natural wetting and drying. Secondary minerals have formed on the bulk fines after two months, regardless of thickness or chamber conditions, with up to a 1.5 g mass increase. Orrock fines (<75 μm) in the CO2 incubator exhibit secondary precipitation, irrespective of sample thickness, displaying white patches (5 mm × 5 mm) on the surface. Upon experiment completion the columns will be sampled and analysed through TGA and total inorganic carbon to monitor CO2 sequestration extent and yield. This study has implications for the use of basalt fines for CDR at quarrying operations.
[1] Beerling, D.J. et al., 2020. Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature, 583(7815): 242-+. [2] Edwards, D.P. et al., 2017. Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture. Biology Letters, 13(4).
