World’s Largest Carbon Capture Plant: Inside 'Mammoth'

A significant milestone in climate technology has been reached in Iceland with the activation of “Mammoth.” This facility, developed by the Swiss company Climeworks, currently holds the title of the world’s largest direct air capture (DAC) plant. It is designed to pull carbon dioxide directly from the atmosphere and permanently store it underground, offering a tangible glimpse into how industrial engineering might help address global warming.

The Giant in the Lava Fields

Located at the Hellisheiði (Hellisheidi) Geothermal Power Plant, Mammoth is a massive expansion of the technology Climeworks previously deployed. In 2021, the company opened “Orca,” which was then the largest facility of its kind. Orca had the capacity to capture 4,000 tons of CO2 per year.

Mammoth is roughly nine to ten times larger. At full capacity, it is designed to capture up to 36,000 tons of carbon dioxide annually. To put that number in perspective, it is equivalent to removing approximately 7,800 gas-powered cars from the road for a year. While this is a tiny fraction of global emissions, the facility serves as a critical proof of concept for scaling the technology to the megaton and gigaton levels needed in the coming decades.

The construction of Mammoth began in June 2022. It features a modular design consisting of 72 collector containers. These containers look like industrial shipping containers stacked in a V-shape. Climeworks plans to have all 72 containers operational by the end of 2024.

How the Technology Works

The process used at Mammoth involves two main stages: capture and storage. The facility relies on a partnership between Climeworks, which handles the capture technology, and an Icelandic company called Carbfix, which handles the storage.

1. Direct Air Capture (DAC)

The “capture” phase is purely mechanical and chemical.

  • Air Intake: Giant fans draw ambient air into the collector containers.
  • Filtration: Inside these collectors, the air passes over specialized filters containing a solid sorbent material. These filters selectively bind with CO2 molecules while letting the rest of the air (nitrogen, oxygen) pass through.
  • Extraction: Once the filters are fully saturated with CO2, the collector closes. The system heats the interior to approximately 100°C (212°F) using geothermal heat. This heat releases the CO2 from the filter, creating a concentrated gas stream.

2. Mineralization (Turning Gas to Stone)

Once Climeworks has concentrated the CO2, Carbfix takes over.

  • Dissolving: The CO2 gas is mixed with water, essentially creating sparkling water or soda water.
  • Injection: This mixture is pumped deep underground into basaltic rock formations, roughly 700 to 2,000 meters (2,300 to 6,500 feet) beneath the surface.
  • Reaction: The acidic water reacts with the basalt rock, releasing metals like calcium, magnesium, and iron. These metals combine with the CO2 to form solid carbonate minerals.
  • Result: Within about two years, the carbon dioxide turns into solid stone. It is permanently locked away and cannot leak back into the atmosphere.

Why Iceland?

Iceland is the ideal location for this technology for two specific reasons: geology and energy.

First, the Direct Air Capture process requires a significant amount of energy, both electricity to run the fans and heat to release the CO2 from the filters. The Hellisheiði power plant creates renewable geothermal energy by tapping into volcanic heat underground. This ensures that the process of cleaning the air does not create new emissions.

Second, the Carbfix storage method requires basalt. Iceland is largely formed of young, porous basalt rock. This rock is highly reactive, which accelerates the mineralization process. In other geological formations, storing CO2 can take centuries to stabilize, but in Icelandic basalt, it happens in under 24 months.

The Economics: Who Pays for It?

One of the biggest hurdles for Direct Air Capture is the cost. It is currently one of the most expensive ways to reduce carbon. While Climeworks does not publicize the exact cost per ton for Mammoth, estimates for current DAC technology hover around \(600 to \)1,000 per ton of CO2 removed.

To make this viable, Climeworks sells “Carbon Removal Services.” High-profile corporate clients purchase these credits to offset their own unavoidable emissions or to meet “net-zero” goals. Current customers include:

  • Microsoft
  • Shopify
  • Stripe
  • Swiss Re
  • JPMorgan Chase

The goal for Climeworks is to use the revenue from these early adopters to fund larger plants, improve efficiency, and drive costs down. The company aims to reduce the cost to \(300-\)350 per ton by 2030, with a long-term target of hitting \(100 per ton by 2050. At \)100 per ton, the technology becomes economically viable for widespread global adoption.

The Scale Problem

While Mammoth is an engineering marvel, experts emphasize that it is not a silver bullet. Global carbon emissions were over 37 billion tons in 2023. Removing 36,000 tons is negligible in the grand scheme of current pollution levels.

However, the International Energy Agency (IEA) has stated that carbon removal is a necessary part of the equation. Even if the world switches rapidly to solar and wind, certain industries (like aviation and heavy shipping) are difficult to decarbonize. DAC plants like Mammoth are intended to clean up those residual emissions and potentially address historic emissions accumulated over the last century.

Climeworks has outlined a roadmap to reach megaton capacity (millions of tons) by 2030 and gigaton capacity (billions of tons) by 2050. This will require building facilities much larger than Mammoth and expanding to other regions, including planned projects in the United States and Kenya.

Frequently Asked Questions

Is the storage safe? Yes. The Carbfix method mimics a natural process that has occurred for millions of years. Once the CO2 mineralizes into stone, there is no risk of it exploding or leaking back into the atmosphere. It becomes part of the local geology.

Does this encourage companies to keep polluting? This is a common concern known as “moral hazard.” Critics argue that if companies believe they can just suck carbon out of the air later, they won’t cut emissions now. However, climate scientists argue we have waited too long to choose one or the other. We now need to cut emissions drastically and develop removal technologies simultaneously to meet the goals of the Paris Agreement.

Can this technology be used anywhere? Not exactly. While you can capture air anywhere, you need a cheap, renewable energy source and the right geological conditions for storage. However, if storage isn’t available on-site, the captured carbon can be utilized for other purposes, such as creating synthetic fuels or carbonated beverages, though this releases the CO2 back into the air eventually.

How much water does it use? The Carbfix process requires substantial amounts of water to dissolve the CO2 (about 25 tons of water per ton of CO2). However, in Iceland, the water is re-circulated from the geothermal plant operations, and since it is injected deep underground, it does not deplete local drinking water supplies. Future versions of the technology may use seawater.