Closing the direct air capture-solar-mineral carbonation (DAC-Solar-MC) loop

Project duration: July 2023–June 2026

Project lead

Team

Robbie McDonald, Phil Green, Graeme Puxty, Phillip Fawell and Paul Feron.

Opportunity

Mining companies are under mounting pressure to fulfil their ‘social licence’ obligations and seek more sustainable solutions to existing practices of tailing management. Globally, approximately 7 gigatonnes (Gt) per year of tailings are produced as wastes and by-products of mineral extraction. Without targeted rehabilitation and remediation strategies, natural weathering and erosion of tailings can cause serious long-term environmental impacts.

Coupling direct air capture (DAC) of carbon dioxide (CO₂) and mineral carbonation (MC) is a relatively new approach that offers the possibility of immediately locking the carbon from DAC using mining tailings from a nearby mineral processing site. The almost pure CO₂ from DAC can significantly accelerate carbonation rates and eliminate the cost and environmental impact of CO₂ transport. The process also generates value-added products that would enhance the economics of the technology for mining companies.

Permanently locking the CO₂ product from a DAC system in long-lasting materials can help in the adoption and widespread application of DAC far beyond the limited number/capacity of geological storage sites. Moreover, it provides an accelerated and efficient carbonation platform for the huge amounts of tailings often left behind from mineral processing. At present, the missing link is combining DAC and MC with clean energy to increase efficiency, and lower cost and energy requirements. To do this, an innovative absorption liquid that would sustainably and affordably capture atmospheric CO₂ and then be regenerated and recycled using less energy and water is needed, together with a rigorous experimental program to formulate and test such a novel absorption formula. While challenging, this provides a significant commercial opportunity for an innovative and sustainable solution to a persistent environmental challenge.

Goal

We’ll focus on high-level process integration to close the loop of DAC-Solar-MC processes and deliver the underpinning science required to induce DAC of CO₂ using solar energy, generate value-added products, and improve the value proposition of the technology.

Our approach is to design a scalable, on-the-spot and on-demand, environmentally-benign SlMiDAC (direct air capture-solar-mineral carbonation) system that can be established on low-class land (relative to other carbon capture technologies), run by renewable energy, with reduced water consumption, and using a novel absorption liquid.

The short-term goal is to establish DAC-MC synergy, where the CO₂ from DAC is directly used in MC. Ultimately, however, we’ll fully integrate the two processes to create a state-of-the-art platform that’s induced by renewable energy and eliminates the middle (desorption) process. This will greatly enhance the sustainability and economics of the DAC-Solar-MC trio. Given the magnitude of mine operations and the significant amount of tailings generated, remediation using atmospheric CO₂ to convert tailings into value-added products, or at least support a stable and self-sustaining ecosystem after mine site closure, offers an attractive proposition for the mining industry and significant commercial outcomes for CSIRO in niche intellectual property generation, and research capability in sustainable, next-generation MC.

Barriers

While cost-effective binding of atmospheric CO₂ in an accelerated mineralisation process is recognised as a fast growing area of research, there is yet to be a breakthrough in identifying a novel absorption formula to integrate DAC with MC.

Current MC routes also have cost and/or efficiency limitations and need rigorous techno-economic analysis and lifecycle assessment comparisons. However, we’ve identified one, combining precipitation and carbonation in fluid, that may be suitable for process integration using ammonia-blend absorption liquids, which offer potential advantages in terms of cost, thermal stability, and lower energy requirements. The absorption liquid can also be directly regenerated in the MC process and recycled back to the DAC absorber. Experimenting with novel absorption liquids is a relatively high-risk exercise but one that the combination of CSIRO’s state-of-the-art equipment, and the skill sets and experience of the project team are well-equipped to meet.

References

Orica Explosives Technology P/L (2018). Integrated chemical process (US patent).
https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/9855526