Portfolio Spotlight: Planeteers - Weathering Limestone Really Fast to Capture and Store CO₂
Controlling the Weathering
The team at Planeteers developed a reactor—engineered to work in a big green shipping container—to accelerate natural carbon capture and storage processes through limestone weathering. As carbon dioxide in the atmosphere gets trapped in water droplets, it forms carbonic acid. This substance decomposes limestone and naturally forms bicarbonate. The stable bicarbonate traps the carbon as it travels through rivers to the ocean where it can remain stored for over 10,000 years.
Under natural conditions, this process takes thousands of years. The Planeteers method of accelerated weathering of limestone (AWL) cuts the process down to mere minutes.
By speeding up the natural process, they created a way to make meaningful progress toward carbon neutrality and begin the repair of our planet.
Though scientifically technical, the process relies on relatively few steps. First, CO2 from a controlled combustion of biomass or biogas is dissolved in water, forming carbonic acid. The Planeteers reactor adds a limestone slurry to the carbonic acid, creating bicarbonate. The mineralised water can be discharged and then safely stored in the ocean.
Not only will the carbon remain trapped in the ocean, it also “heals” as the increased alkalinity of the water can fix part of the ongoing acidification of the water due to climate change.
By controlling the process, Planeteers can determine precisely how much carbon dioxide has been extracted and stored, which enables tremendous potential for scaling.
Where in the world is all the CO2?
One of the primary advantages of AWL compared to EW processes is that they can go straight to heavy pollution sources and mitigate effects more efficiently, rather than relying on ambient conditions.
Setting up their reactor near factories, Planeteers can capture CO2 at the source and immediately flush it through the system before releasing the mineralized water into a natural body of water
Trapping the CO2 at the point of exhaust or at chimneys enhances the process, speeding up the reaction compared to working with ambient air (where the CO₂ is only available at 0.04%) and simultaneously ensuring no loss of carbon dioxide.
Unlike many carbon capture and storage methods, AWL can be implemented almost anywhere with a consistent supply of water. Particularly beneficial at wastewater facilities, (biogenic) power plants, and in hard-to-abate industries such as lime and cement production, the reactors offer an incredibly mobile solution. Once tuned to a local water source’s natural alkalinity, the reactors can dilute the final mineralized water as necessary to ensure no negative effects end up downstream from oversaturating the water.
Giga Scaling
After building and testing their first reactor unit, capable of sequestering 60 tonnes of CO2 per year, in their garage in Hamburg, Planeteers began their field testing in summer 2024.
With the real-life data gained from their first model, they completed a fundraising round and began work on a larger, more refined unit capable of capturing 1,000 tonnes of CO2 in a year.
Their current industrial development aims to create a reactor capable of pulling 2,500 tonnes per year, scaling to 10,000 tonnes of CO2, with the targeted goal of reaching one Megatonne by the end of the decade.
Benefits of a Planeteers’ Reactor
Planeteers’ reactors mimic the natural limestone weathering that occurs all around us, condenses it into a shipping container, and turns thousands of years into minutes.
As a result, measurement, reporting, and verification (MRV) tools allow for accurate analyses and measurements of CO2 captured. Other EW methods are working in “open systems” like the soil or the ocean making accurate measurements really hard. Planeteers can constantly measure accurate levels in dispensed mineralized water without guesswork.
The entire process relies on geochemical reactions, and the reactors demand less energy than many carbon capture methods. Emission-intensive industries like cement or lime can almost seamlessly integrate Planeteers’ technology, especially as they process limestone, leveraging side-streams and byproducts of these industrial processes to create an ecosystem in which industrial waste becomes fuel for climate mitigation strategies. A changed perception for these massive industries—from damaging the planet to helping it heal—could spark a widespread change in how industries approach production.
Adding a Little Magic
Looking ahead, the team has started the development of a second technology. Rather than adding mineralized water directly to local streams and rivers, the bicarbonate can be further manipulated into hydrated carbonate mineral (HCM). This “meta-stable” material dissolves quickly in water, creating a reaction that enables the water source to pull carbon dioxide directly from the atmosphere. Applied at large scale, this technology could leverage the improved capacity of the oceans to pick up more carbon dioxide.
All together, the work started in Hamburg, Germany, can bring change to the planet while protecting a key element necessary to adoption: people.
It would seem easy to eliminate carbon emissions by cutting out industries with massive output, yet people typically cling to what feels familiar, safe, and comfortable. True progress in climate change requires pragmatic solutions—things that keep some pleasures and keep food on the table, not living off the grid or leaving no mark on society.
The goal for Planeteers isn’t a world without carbon emissions or to give a “free pass” to old industries to remain as they are, it’s a world future generations get to enjoy in a sustainable balance.
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