Developing enhanced weathering methods in mine tailings for CO2 sequestration

Project Information

DETAILS

Grant agreement ID: 101018312

DOI

10.3030/101018312

Project closed

EC signature date 19 April 2021

Start date 1 January 2022

End date 31 December 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 172 932,48

EU contribution

€ 172 932,48

Coordinated by

AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
Spain

Periodic Reporting for period 1 - DETAILS (Developing enhanced weathering methods in mine tailings for CO2 sequestration)

Reporting period: 2022-01-01 to 2023-12-31

Summary of the context and overall objectives of the project

Throughout geological history, the Earth has naturally moderated atmospheric CO2 through chemical weathering of rocks, a process that converts atmospheric CO2 into hydrogen carbonate and carbonate ions, known as alkalinity, or as precipitated solid carbonate minerals. These processes typically occur over thousands of years or longer. Based on these natural principles, one CO2 removal method that aims to capitalise on the Earth’s natural processes is through enhanced weathering of rocks. The aim is to speed up this natural weathering process so that instead of it happening over thousands of years, it happens over tens of years, to combat climate change.
The principle of the method is to weather the minerals that are contained within the rocks. Silicate minerals which also contain calcium and magnesium can react with CO2 and water in the atmosphere. There are ways to speed the reactions up. For example, by grinding the rocks to smaller grain sizes, we achieve better exposure of the rock to CO2. We can also speed up the reactions by using more concentrated CO2 gases, increasing the temperature, using acidic solutions for the reactions or by using microbial communities that can help break down the minerals.
Since small grain sizes, such as sand size grains or finer, are beneficial for enhanced weathering, one potentially significant material for CO2 removal is the unwanted rock wastes that are stockpiled at mine sites. We call these wastes mine tailings, and they are the remaining crushed up rock powders that are left behind after the metals or economic minerals have been extracted.
Mine wastes are useful because they are already fine grained, as mine companies require significant rock size reductions in order to harvest the metals and minerals that they are targeting. Tailings are essentially stored as powders on the site. There is also lots of it available, as society needs a lot of mined resources to function.
We investigated the different waste streams at the mine site to identify the best minerals and best mine wastes for CDR purposes. We looked at the chemistry and mineral content of the different streams through chemical and mineralogical analysis. After we identified our potentially useful waste streams, we tested them directly, separating out the best individual minerals to test their reactivity with water and CO2.
Once potential for CO2 removal through any of the produced wastes was identified, we determined methods to speed up the reaction, either by harnessing high temperatures, high pressures, concentrated CO2, develop acidic conditions through the use of microbial materials, better exposure to the atmosphere (e.g. spreading) or any further crushing and/or separation that can be realistically achieved. We then looked to scale up the experiments, taking the work beyond the laboratory scale up to a big enough scale to use on the mine site. By taking this approach, we were able to select the most appropriate materials and strictly monitor the changes to the mine wastes and calculate the CO2 removal along the way. If we needed to change the system, we did so in real time.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Publications:
• Bullock et al., 2023. Experimental investigation of multiple industrial wastes for carbon dioxide removal strategies. International Journal of Greenhouse Gas Control, 129, p.103990.
• Alcalde … Bullock et al., 2022. Preface: State of the art in mineral exploration. Solid Earth, 13, 1161–1168.
• Bullock et al., 2023. Catalogue of South African mine tailings for geochemical carbon dioxide removal purposes. International Journal of Greenhouse Gas Control, 124, p.103844.
• Bullock et al., 2023. Geochemical carbon dioxide removal potential of Spain. Science of The Total Environment, 867, p.161287.
Conference proceedings:
• Bullock et al., 2022. Investigating multiple mine tailings for enhanced weathering methods and CO2 sequestration. Goldschmidt Conference.
• Bullock et al., 2022. Geochemical Carbon Dioxide Removal – Research in Progress Meeting.
• Bullock et al., 2023. Experimental investigation of multiple industrial wastes for geochemical carbon dioxide removal strategies. EGU 2023.
• Tornos, Bullock et al., 2023. Geochemical carbon dioxide removal potential of Spain. EGU 2023.
• Weeks, Khatiwala, Bullock, et al., 2023. Efficiency of carbon dioxide removal by ocean alkalinity enhancement via enhanced weathering of mine tailings. EGU 2023.
• Bullock et al., 2023. Geochemical carbon dioxide removal potential of Spain. Double Nature Summit.
• Bullock et al., 2023. Experimental investigation of multiple industrial wastes for geochemical carbon dioxide removal strategies. Goldschmidt Conference.
• Bullock and Fernandez-Turiel, 2023. Enhanced rock weathering opportunities in Spain. ERW23.
Oral Presentations:
• Bullock et al. Developing enhanced weathering methods in mine tailings for CO2 sequestration. Project Vesta, 2022.
• Bullock et al. Using mine wastes and other industrial by-products for geochemical carbon dioxide removal strategies. Lawrence Berkeley National Laboratory, University of California, 2022.
• Regueiro González-Barros, et al. The Innolog project. Prospectors and Developers Association of Canada, 2022.
• Bullock et al. Investigating the use of industrial by-products for geochemical CO2 removal strategies. Herriot-Watt University RCCS-Negative Emission Technologies Group, 2023.
• Bullock et al. Geochemical carbon dioxide removal potential of Spain. Geosciences Barcelona-CSIC, 2023.
• Bullock. Developing methods in mine tailings for CO2 sequestration. IE University, Segovia. 2023.
• Bullock. Hot rocks and cool solutions: A geologist's path from volcanic rocks to carbon removal. Wirral Grammar School for Boys, Wirral, 2023.
• Bullock. Developing methods in mine tailings for CO2 sequestration. CEGM-UBA, University of Buenos Aires. 2023.
Conference convenings:
• SSP3.5 - Microbial and abiotic minerals: processes and archives of environmental change. EGU 2023.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The aim was to identify the materials that showed suitable potential for CO2-water-material reactions for targeted future upscaled and accelerated removal strategies. Changes to water chemistry through reactions with CO2 and powdered material samples were monitored throughout the duration of the experiment. These included changes to pH, alkalinity indicators (CaO, CaCO3 and H+), silica content and cation content (labile cations leaching from solid samples under near-ambient conditions), predominantly Ca2+ and Mg2+, required for reactions with CO2 (available as dissolved inorganic carbon; DIC) to produce bicarbonate (HCO3-, stabilised by cations) and carbonate (CO32-, stabilised by cations) ions. A better understanding of reaction kinetics for a wider range of industrial wastes has helped to steer current and future directions and complimentary projects to confirm or re-consider the viability of materials for CDR schemes, and to identify opportunities for upscaled pilot schemes with further implemented geochemical CDR methods to speed up reaction kinetics.
This proposal has gone beyond the current state-of-the-art by focusing on delivering on-site testing and pilot schemes on a range of voluminous and suitable materials with industry partners.

Linked themes across Earth processes, industrial by-production and exploration activities