Direct air capture that is economic and actionable.

8 Rivers Capital invented Calcite and has been advancing the technology in its labs and in collaboration with the Massachusetts Institute of Technology, with further funding from the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) FLECCS program.  Calcite’s process captures CO2 directly from air and sequesters it underground, aiming to support the world’s climate targets by removing over a billion of tons of CO2 for less than $100 per ton.

8 Rivers is rethinking direct air capture to cost effectively meet the global goal of net zero by 2050.

Calcite is a phase I winner of the X Prize for Carbon Removal


About the project:

Direct Air Capture is a key technology in the pursuit of meeting the global goal net zero by 2050. The rising levels of CO2 in the atmosphere are only going to accelerate the worst effects of climate change. The world not only needs to reduce emissions, but they need to be actively removed from the atmosphere. However, due to the low concentration of CO2 in the air, it is thermodynamically and economically costly to remove. Therefore, carbon removal solutions must find innovative approaches to reduce the cost as much as possible to be successful. Calcite’s advantage is it’s simplicity. Calcite was intentionally designed to minimize technical complexity and costs. The Calcite process passes ordinary air with approximately ≈415 PPM CO2 across calcium hydroxide in a large warehouse, absorbing CO2 from the air into calcium carbonate crystals, similar to how concrete sidewalks dry and absorb carbon in the process. The calcium carbonate that’s created is cycled into a kiln to regenerate calcium hydroxide and capture CO2. The Calcite process accelerates the carbonation of the calcium. Because CO2 from around the world mixes in the atmosphere, Calcite can be located in the most cost effective regions to maximize its carbon removal and minimize the cost.


CO2 in the atmosphere is already at a dangerously high level and is only rising. To help offset the worst effects of climate change, CO2 must be directly removed from the air at reasonable cost.

Key Innovation

Calcite’s advantage is simplicity and speed. The process uses the natural carbon absorbing properties of Calcium Hydroxide and is able to accelerate its absorption of CO2 at low cost.


A cost-effective and scalable method to pull CO2 directly from the air.



Lab testing has completed. Pilot scale development is currently underway.


Calcite’s technical approach focused on optimizing chemistry while reducing technical risk as much as possible.


With economics driving the design, the system captures CO2 for permanent underground storage at exceptionally low-cost.

Commercially Available

Calcite uses readily available and well understood industrial equipment making the technology deployable today.


Calcite’s unique design and reliance on abundant non-toxic materials enables it to rapidly scale up to meet the global need for carbon removal.

Direct air capture is a critical tool to carbon reverse emissions. Calcite has the potential to remove over a billion tons of CO2 from the atmosphere.

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