As an EU Member State, Spain is required to adopt national soil, energy and environmental plans to make notable progress on its climate actions and land use management policies. A recent study [1] highlighted the high potential for Spain to host viable geochemical CO2 removal (CDR) schemes to make valuable contributions towards national reduction targets, EU environmental regulations and global climate goals. Spain hosts a notionally high CDR capacity thanks to extensive mafic-ultramafic rocks, high industrial by-product tonnages, and appropriate land uses to host projects. Enhanced rock weathering (ERW) was highlighted as one potential CDR strategy that could be pursued within Spain. This study aims to expand on these initial findings to better constrain ERW feedstocks, host settings and synergistic approaches within Spain.
Due to suitable bedrock geology and viable feedstock providers within the regions, there are possibilities for ERW schemes to be hosted within Galicia, Andalucía, Castilla-La Mancha and the Canary Islands. Of these regions, Galicia (northwest Spain) has been pinpointed for more detailed investigations based on the high reactivity of rocks that are exploited across the region (e.g., dunite, peridotite, serpentinite and amphibolite). The temperate and rainy climate of Galicia is beneficial for crop production, and would also encourage ERW if implemented. Extensive agricultural coverage, targeted restoration areas, mined and quarried land and extensive coastline exposure could provide suitable ERW site opportunities across Galicia.
One potential barrier for widescale ERW implementation in Galicia is the general prevalent soil conditions across the region. Soil pH in Galicia are typically ultra-acidic (<3.5) to acidic (5.2), containing high concentrations of chromium and nickel. Soils with a pH <5.2 may be considered unsuitable candidates for ERW approaches, as dissolution of minerals by non-carbonic acids would not produce alkalinity, thus reducing CDR efficiency. As a complementary approach to ERW and means of mitigation, specifically-designed technosols, soils created by human intervention, could be utilised to improve soil health, enhance soil carbon storage and act as a long-term carbon sink. Technosols have been used on degraded soils in Galicia for remediation purposes, restoring health and value to soils in industrial areas. It is considered that mixed technosol-ERW feedstock approaches could act to alter soil pH, nutrient availability, physical properties, microbial communities and plant growth to increase soil organic and inorganic contents.
ERW opportunities of Spain, specifically Galicia, have been assessed through geochemical modelling, benchtop experiments, fieldwork and GIS-based approaches. The occurrence and availability of mafic-ultramafic rocks and industrial wastes in areas proximal to degraded soils and agricultural lands provide opportunities to explore joint technosol-ERW feedstock approaches, with the intention of achieving multiple benefits – notably, enhanced CDR (with potential upscale in Spain, across the EU and beyond) and improved soil health.
This work forms part of the DETAILS project (Developing enhanced weathering methods in mine tailings for CO2 sequestration; Marie Skłodowska-Curie grant agreement ID: 101018312).
References: [1] Bullock et al., 2023. Geochemical carbon dioxide removal potential of Spain. Sci. Total Environ., 867, 161287.