ELi5: how does carbon capture work?


I get that we would trap carbon but could it fail and potentially cause a mass release?

In: Earth Science

[Photosynthesis](https://en.wikipedia.org/wiki/Photosynthesis). 6 carbons (carbon dioxide) + 6 water -> 1 sugar + 6 oxygen. The plant then chains the sugars together into [cellulose](https://en.wikipedia.org/wiki/Cellulose), which forms the body of the plant.

The carbon is thus trapped in plants (trees and such). It generally doesn’t get released until said plant is burned, or eaten. Animals generally use the reverse process: cellulose -> sugar, and sugar + oxygen (breathed in) -> water + carbon dioxide (breathed out), releasing the carbon.

The goal of carbon capture is find a way to store is such that that’s really not a concern.

For example, one method is to have farmers take their leftover crops (think stalks leftover after picking), push it into a pile, throw a cover on it, and light it on fire. This will make charcoal. Then they can till it into the soil.

This actually improves the soil quality, and helps return the nutrients to the soil. But charcoal doesn’t decompose, and it largely acts as a filler in soil. And buried in soil it’s not going to burn either. So there isn’t really a serious risk that this charcoal will return to the atmosphere anytime soon (it really requires digging all the dirt up and burning it, it won’t burn just in the ground).

Like the above method, a major part of carbon capture is doing something with it after it’s captured, you either sequester it by converting it into something that can be stored long term, or you use it (such as to make biofuel), biofuel will release it back into the atmosphere, but since it’s from carbon capture, it’s carbon neutral.

It doesn’t work very well.

It might make sense to capture carbon in wood and them carefully store that wood in an underground salt mine for millions of years, but that’s not what’s happening. Pushing it underground could lead to ao CO2 “gusher” that releases if back all at once or slow cracks (we could call it fracking) that lets it leak out slowly.

We have people that won’t tolerate nuclear waste like radioactive gloves cast in concrete, the concept of underground CO2 storage is actually a lot more dangerous.

One method (of many under investigation) involves growing wood, often a fast-growing one like willow. That takes in carbon dioxide from the air into its structure. But remember it has to be kept forever, not just until it decays and released it again.

So the aim is to burn it in a reduced oxygen atmosphere. Some of the wood combusts but the heat it produces when it does turns much of the load into charcoal, virtually pure carbon. That is very stable and can be buried and it will stay as locked up carbon.

Basically it’s an updated version of what charcoal burners used to do in ages past!

In some cases, CO2 is pumped into the ground to repressurize oil formations, for enhanced extraction. If the CO2 remains as a gas, I guess there’s a risk of a blowout.

For long term storage the carbon needs to be converted to some non-volatile form. Into charcoal, as mentioned, or into carbonate minerals. E.g.

> Since 1990, scientists and engineers considered using naturally occurring minerals that react with CO2 to form carbonate minerals, as a means to capture CO2 from the atmosphere and store it in solid form where it will remain stable for thousands or millions of years (Seifritz, Nature 1990). The mineral olivine (Mg2SiO4) has been the focus of the most research. Olivine forms the carbonate mineral magnesite via reactions such as

> > Mg2SiO4 (olivine) + 2 CO2 (from gas or fluid) = 2MgCO3 (magnesite) + SiO2 (quartz)

> Olivine is abundant, has more magnesium than silicon, and reacts readily because it is far from equilibrium with the atmosphere and surface waters.