Mechanochemical processing of silicate rocks for direct carbon capture (MACO2)

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This project aims to develop a new technology for capturing carbon into waste rock powders that are naturally formed during mining and aggregate production operations. We aim to use mechanochemical reactions, which occur during rock crushing, to permanently trap CO2 from industrial exhaust gases as a means of carbon capture. During crushing, energy is instantaneously released (as charged particles and photons) when the chemical bonds in the rock are broken. We use this mechanochemical energy to trap CO2. Our recent research, published in Nature Sustainability, showed that if you crush silica-rich rocks, such as granite and basalt, in CO2 gas instead of air, the CO2 can become permanently trapped, via a process of chemical sorption, within the crystal lattice of the crushed particles. This project will build on our early research. We will explore the effects of temperature, crushed particle size and initial rock water content on the amount of CO2 trapped per unit mass of crushed rock. We will also investigate gas stream composition. Our previous research used pure CO2: here we will crush rocks within realistic CO2-rich effluent gases from industries such as cement production, biomass power production, gas and hydrogen production from natural gas. We will evaluate the carbon savings from our technology using life cycle analysis. Finally, we will explore the potential for (1) the final rock powders to be used as a partial cement replacement product, and (2) co-production of valuable metals from the CO2-rich rock powders. This research project could have a major impact on our ability to meet net zero carbon targets by 2050. Worldwide, at least 40 billion tonnes of silicate-rich rocks are crushed every year by the mining and quarrying industries. If we can adapt current rock crushing processes to trap CO2, with very little extra energy expenditure (other than that used to transport the CO2), then this could be used to trap greenhouse gases from 'hard to decarbonise' industries. Based on our published early research findings, at least 0.4MtCO2 of thermally-stable and insoluble CO2 can be trapped for every 100Mt of saleable crushed aggregate. We estimate that, if this technology was developed and adopted worldwide, it could capture ~0.5% of global CO2 emissions, or 175MtCO2 annually: this is equivalent to the CO2 trapped by a mature forest the size of Germany.