Looking into fundamental geochemical processes of mineral carbonation

September 29th, 2023

Unravelling molecular-level processes to accelerate mineral carbonation of carbon dioxide

Project duration: July 2023–June 2026

Image: Back-scattered electron micrograph shows porous and fibrous Mg-Ca silicates and carbonate minerals growing on the surface of mafic minerals after reaction in carbonate solutions for 4 weeks. Image courtesy of Yanlu Xing.
Image: Back-scattered electron micrograph shows porous and fibrous Mg-Ca silicates and carbonate minerals growing on the surface of mafic minerals after reaction in carbonate solutions for 4 weeks. Image courtesy of Yanlu Xing.

Project lead

Dr Yuan Mei

Dr Yuan Mei

Team Leader, Experimental & Computational Geochemistry

Team

Yanlu Xing, Weihua Liu, Nick Owen, Shu Huang and Nathan Webster.

Opportunity

Mineral carbonation offers a promising approach to capturing atmospheric carbon dioxide (CO2) by reacting it with rocks to form stable carbonate minerals and enable long-term storage. Research on mineral carbonation has gained momentum in recent years, but to accelerate what is a very slow, naturally-occurring geologic process it’s crucial to solve some fundamental geochemistry questions related to the reaction mechanisms and physicochemical controls of mineral carbonation.

The conversion of CO2 to carbonate minerals involves several steps that are not well understood. Calcium, magnesium, iron and silicate elements, at the molecular level, which determine the bulk reaction processes, are also unclear. Other areas of potential research include reaction mechanisms, chemical thermodynamics and kinetics, which can be used to identify particular aqueous species and minerals that contribute to the dominant CO2-fixing reactions.

Studies over the past two decades have shown that the complexity of natural rocks and the limits of our current knowledge prevent us from understanding the chemical processes during carbon mineralisation. A molecular-scale investigation of mineral carbonation is the breakthrough in research that’s required to develop well-controlled, efficient and cost-effective mineral carbonation methods.

Goal

Fixing CO2 as stable minerals in the vast number of natural rocks available is still one of the most promising ways to realise significant emissions reduction.

Our project aims to unravel the reaction mechanisms, kinetics and mineral morphology evolution of individual minerals exposed to CO2-bearing fluids. We’ll do this using a unique approach that combines mineral replacement experiments with molecular simulations to study reaction mechanisms, measure and calculate thermodynamic and kinetics properties, and gain a molecular-level understanding of CO2-fluid-mineral interactions. We’ll leverage CSIRO’s state-of-the-art facilities and our existing research capabilities and experience to unlock the fundamental geochemistry knowledge that’s crucial for an efficient and effective accelerated mineral carbonation process.

Barriers

At present, the most significant barrier to actively capturing and storing CO2 via mineral carbonation is the lack of understanding of the carbonate precipitation mechanisms and silicates breakdown reactions involved. Our approach has great potential in understanding mineral carbonation reactions at atomic to micro-scales but has not been widely employed in mineral carbonation research.

Rather than attempting to react a single fluid agent with multiple minerals in the rock (which lowers reaction efficiency and dramatically increases the chemical complexity) we’ll target specific minerals that can already accommodate significant amounts of CO2 (i.e., rich in calcium, magnesium and iron) and are preferentially reacted with CO2-carrying fluids.

In previous studies we’ve demonstrated that using mineral replacement experiments like these, combined with molecular simulation, can provide comprehensive knowledge about element behaviour, micro-structure, thermodynamics and kinetics of mineral carbonation reactions. With this information, we can then accurately model mineral carbonation reactions at various temperatures, pressures and fluid/mineral compositions, which will enable us to build realistic geological model for permanent large-scale carbon storage. There are also challenges with our experimental module in achieving the timescale of mineral carbonation in real life and, in the modelling module, the challenge is one of scale (reproducing the real system in a small simulation box). We’ll use our previous experience in interpreting experimental and simulation results. We will also collaborate with scientists in reactive transport modelling at different time/space scales to overcome these challenges.

References

Xing, Y., Brugger, J., Etschmann, B., Tomkins, A. G., Frierdich, A. J., & Fang, X. (2021). Trace element catalyses mineral replacement reactions and facilitates ore formation. Nature communications, 12(1), 1388.

Snæbjörnsdóttir, S. Ó., Sigfússon, B., Marieni, C., Goldberg, D., Gislason, S. R., & Oelkers, E. H. (2020). Carbon dioxide storage through mineral carbonation. Nature Reviews Earth & Environment, 1(2), 90-102.