This article discusses different carbon mineralization methods, their limitations, and the benefits of carbon mineralization for the mining industry.
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What is Carbon Mineralization?
Carbon mineralization refers to removing carbon dioxide from the atmosphere and storing it in solid minerals, primarily carbonate minerals, such as magnesites, calcites, or dolomites.
The process involves a chemical reaction when specific rocks are exposed to carbon dioxide.
Carbon mineralization has gained attention in recent years to remove atmospheric carbon dioxide, responsible for global warming and climate change.
Mineralized carbon cannot escape back into the atmosphere, which is a significant advantage of this process over carbon storage in porous sedimentary reservoirs.
Carbon mineralization occurs naturally during weathering of calcium and magnesium-rich rocks, specifically peridotite and silicate materials, such as wollastonite, serpentine, and olivine. The natural mineralization of carbon can be accelerated artificially through various methods.
Different Carbon Mineralization Methods and their Limitations
Carbon mineralization methods involve carbon dioxide storage in carbonate minerals/solid storage or combined mineral capture and storage. Solid storage can be realized through ex-situ carbon mineralization, surficial carbon mineralization, and in-situ carbon mineralization.
In ex-situ carbon mineralization, solid reactants are transported to the carbon dioxide capture site and react with carbon dioxide-rich gas or fluid.
Carbon dioxide-rich gas or fluid reacts with alkaline industrial wastes, mine tailings, or reactive rock fragment-rich sedimentary formations that possess a significant proportion of reactive surface area in surficial carbon mineralization.
In situ carbon mineralization is achieved by circulating carbon dioxide-rich fluids through suitable rock formations at depth.
Combined mineral capture and storage can be realized through in situ or surficial carbon mineralization processes using natural surface waters instead of carbon dioxide-rich fluids.
Although in situ mineral capture and storage potentially has a larger storage capacity and lower cost than surficial methods, issues related to the reactive surface area, reaction rate, and permeability are the s disadvantages of this method.
Surficial carbon mineralization uses mafic and ultramafic mine tailings, which have a higher surface area-to-volume ratio than subsurface geologic formations, leading to increased reactivity.
Mine tailings also represent low-cost sources, specifically when generated as wastes of ultramafic/mafic rocks mined or quarried for other vital resources, such as diamonds, nickel, chromium, and platinum group elements.
However, mine tailings can consume less than 36 Mt of carbon dioxide annually and require transportation facilities and large disposal areas. Grinding and mining rock for mineral capture and storage of carbon dioxide could be as expensive as direct air capture systems that require additional energy input and technologies for carbon dioxide storage.
The extent of carbon mineralization primarily depends on the available carbon dioxide dissolved in the solution, available alkalinity in the solution, and chemical conditions that promote the available alkalinity through carbonate precipitation and mineral dissolution.
High pH accelerates carbonate precipitation, while low pH facilitates mineral dissolution. However, several studies have combined carbonate precipitation and mineral dissolution in a single step.
Magnesium and calcium-rich, highly reactive rocks from Earth’s deep interior, including ultramafic intrusions, basaltic lava, and mantle peridotite, act as the vital source of alkalinity for carbon mineralization as these rocks contain pyroxene and olivine minerals.
Although wollastonite reacts more rapidly with carbon dioxide than pyroxene and olivine, the mineral has limited availability. For example, the estimated global reserves of wollastonite are approximately 100 million tons, with less than one million tons of natural wollastonite produced annually in 2016 and 2017.
Olivine, a critical mineral constituent of the upper mantle, is highly reactive to carbon dioxide-rich fluids like wollastonite. The mineral is found at partially hydrated peridotite massifs exposed at Earth's surface. Olivine in the ultramafic intrusions and mantle often contains 88 to 92-mole percent of the magnesium-endmember forsterite.
However, engineered pH swing methods are necessary for olivine carbonation as olivine dissolves slowly at neutral to high pH, and aqueous fluids with high partial carbon dioxide pressure have extremely low pH for extensive carbonate precipitation.
Novel Method Accelerates Carbon Mineralization and Facilitates Critical Mineral Extraction from Mine Tailings for the Mining Industry
The mining industry can use carbon mineralization methods, specifically surficial carbon mineralization, to carbonate their tailings to offset the on-site carbon-dioxide equivalent emissions. This helps realize net-zero emission during mineral extraction, lowering the carbon footprint.
Carbon mineralization can also mitigate health hazards from the asbestos-bearing mine tailings. Moreover, the approach facilitates the production of valuable commodities from mining waste with nearly-net-zero emissions.
A new method has been developed by the Michigan Technological University that significantly and efficiently accelerates the permanent sequestration/mineralization of carbon dioxide. It also facilitates the extraction of critical minerals from mine tailings/low-grade ores.
Critical minerals, such as rare earth elements, cobalt, and lithium, can be produced commercially from abandoned mine tailings as the concentration of these minerals in mine tailings is often higher than in primary ores.
In this method, mine tailings generated from mining operations and carbon dioxide captured from the atmosphere are combined in an accelerated carbonation reactor to produce carbonated products, siderite and magnesite.
These minerals can be stored safely and permanently in a subaqueous tailing pond. This technology is expected to mineralize 2.2 million tons of carbon dioxide annually in mine tailings. Olivine present in mine tailings is used as a carbon sink.
Carbon dioxide sequestration using olivine typically requires several years. However, the new method significantly accelerates the kinetics of mineralization and achieves complete mineralization in four hours.
Moreover, the method also allows the extraction of energy-relevant metals from silicate minerals for battery manufacturing, making it a commercially viable technology. This method can effectively enable the mining industry to realize both net-zero emissions and higher production of critical minerals.
The Future of the Carbon Mineralization Industry
The United States (US) Department of Energy (DoE) has granted a significant amount to this project, titled “Energy Reduction and Improved Critical Mineral Recovery from Low-Grade Disseminated Sulfide Deposits and Mine Tailings”, from Mining Innovations for Negative Emissions Resource Recovery (MINER), a new initiative to fund technology research that improves mineral yield while decreasing the carbon dioxide emissions and required energy to mine and extract energy-relevant minerals.
To summarize, the rising concerns regarding climate change and global warming will increase the need for net-zero emissions in mining operations and the reduction of atmospheric carbon dioxide, leading to the greater adoption of carbon mineralization methods. The mining industry can adopt novel carbon mineralization methods to eliminate on-site emissions when the mine tailings are suitable for carbon sequestration.
References and Further Reading
Sarker, S. K., Haque, N., Bhuiyan, M., Bruckard, W., Pramanik, B. K. (2022). Recovery of strategically important critical minerals from mine tailings. Journal of Environmental Chemical Engineering, 10(3), 107622. https://doi.org/10.1016/j.jece.2022.107622
Kelemen, P., Benson, S. M., Pilorgé, H., Psarras, P., Wilcox, J. (2019). An Overview of the Status and Challenges of CO2 Storage in Minerals and Geological Formations. Frontiers in Climate, 1. https://doi.org/10.3389/fclim.2019.00009
Geiger, K. (2023) Michigan Tech Awarded $2.5 Million to Unlock Net-Zero Emission Mineral Extraction Technologies in Mining Industries [Online] Available at https://www.mtu.edu/news/2023/01/michigan-tech-awarded-25-million-to-unlock-netzero-emission-mineral-extraction-technologies-in-mining-industries.html (Accessed on 25 January 2023)
Making Minerals-How Growing Rocks Can Help Reduce Carbon Emissions [Online] Available at https://www.usgs.gov/news/featured-story/making-minerals-how-growing-rocks-can-help-reduce-carbon-emissions (Accessed on 25 January 2023)
Carbon Mineralization of CO2 [Online] Available at https://www.ncbi.nlm.nih.gov/books/NBK541437 (Accessed on 25 January 2023)
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