TL;DR

We know how to capture carbon from the atmosphere, now we need to decide what to do with it. The goal is to lock it away permanently, or for as long as possible, all while inputting as little energy as possible.
Trapped CO2 itself also has value as it can be transformed into various useful industrial products. In this case, we are locking up the CO2 and displacing the production of new (usually very high emissions) materials.

Carbon storage

There are many ways we can draw carbon out of the atmosphere. From direct air capture to nature-based solutions like reforestation and algae farming, we have the tools and techniques at our disposal. The next question at hand is, what do we do with all of that carbon once we have captured it from the atmosphere? The best case scenario is for long-term, or better yet permanent, utilization and storage of carbon to ensure we don’t release it back into the atmosphere.

Source: Science, 2018

Permanent storage vs carbon neutral utilization

There are two primary ways to look at what happens to carbon once we have removed it from the atmosphere. We can either lock it up permanently, or we can turn it into something that will eventually re-release that carbon back into the atmosphere. The latter case isn’t necessarily bad because it wouldn’t be adding more carbon to the atmosphere (like burning fossil fuels does), but the longer we can lock it up, the better off we will be.

A very non-scientific generalization of the permanence associated with a variety of carbon storage options. The position of each method on this scale can vary greatly depending on how it is employed and how the material is used.

Methods of carbon storage

Mineralization

This technique uses the natural process of silicate rock weathering that traps CO2 permanently into mineral structures—weathering being the breakdown or deterioration of rock material, in this case, silicates like basalt.

When it rains, some of the CO2 in the atmosphere gets mixed up with water, forming carbonic acid that dissolves rocks. Much of that dissolved material eventually runs into the ocean, where another reaction takes place, and the rock particles react with CO2 in the ocean water to produce carbonate minerals that finally lock up the CO2.

Source: ClimateScience.org

The natural process works very slowly, trapping around 1 gigatonne of CO2 annually, but we can speed this process up by crushing rocks and exposing more of the surface to the atmosphere (even faster if heat is applied).

<aside> 💡 Rain + Rocks = trapped carbon AND ⬆ rock surface = ⬆ trapped carbon

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