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Comment by sightbroke | Hacker News Reader

> The company spreads crushed basalt on small farms in India and Africa. The silica-rich volcanic rock improves the quality of the soil for the crops but also helps remove carbon dioxide from the air. It does this by reacting with dissolved CO2 in the soil’s water, turning it into bicarbonate ions and preventing it from returning to the atmosphere

> Carbon dioxide in the air dissolves into rainwater, forming carbonic acid. As rocks are worn away (or weathered) by this slightly acidic water, silicate minerals in the rock dissolve. This releases calcium, magnesium, and other positively charged ions called cations. These cations react with carbonic acid in the water, forming bicarbonate ions.

Here is a dumb question: Would the basalt capture CO2 more effectively if released into the atmosphere or into rain storms?

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I've been wondering for a while now about the viability of asteroid/lunar mining that involves returning the payload of rare earth minerals or titanium in flying wing shaped return vehicles that are wrapped in some sort of mineral that ablates in the atmosphere while absorbing CO2 like this stuff does.

The idea is that we could both eliminate the Earth based pollution associated with mining while sequestering co2 previously emitted by terrestrial mining at the same time.

AFAIK cationic calcium, et. al., combine with dissolved CO2 forming carbonates which having low water solubility eventually precipitate out of solution. Area with "hard water" often have issues with buildup of scale in water pipes. The scale is mainly calcium carbonate and sulfate.

This is normally a gradual process requiring ample moisture. Releasing finely ground rock into the air wouldn't likely be effective. For one thing, such dispersal would be rather dilute. IOW the dispersion wouldn't reliably react with CO3 ions before settling out of the air. Another consideration is the salicaceous content of the rock being a potential health hazard.

The original idea of adding crushed rock to water-containing soil is logically the best way for the project to accomplish its goals.

> Would the basalt capture CO2 more effectively if released into the atmosphere or into rain storms?

Guess: it would do so more quickly, but not necessarily more effectively in the long run to the extent it balances the energy required to loft it. (Even if it's all green. You could just that energy to grind and distribute more basalt to the ground.)

You’d need to, at the very least, make it into a powder or it would just fall to the ground anyway. That, in turn, would require you to crush basalt, which is pretty tough and, importantly, energy intensive. And you wouldn’t have any agricultural benefits either.

They're already crushing it here though?

You can still do both things but if the primary goal is to capture carbon my question is if it would capture more if released in the atmosphere (by planes or similar).

You'd want to crush it much more finely for it to have a chance to actually capture anything while in the air, requiring more energy input and causing breathing hazards due to the fine particulates, not to mention staining everything it rains on with the fine basalt.

You could release it extremely high such that it stays suspended a bit longer, but then you'd waste even more energy getting it up there.

there will be very very little dust fine enough to become suspended in air, without running it through ball mills, which will be stupidly expensive. "crusher dust" is the label given to the fines from rock crushers, that is suitable for use on trsditional "gravel paths" in parks. Basalt is actualy quite friable, and crumbles fairly easily......depending on the type...., some would be more trouble than it's worth.....other types are very crumbly and adding the rock to agricultural soils, has the added benifit of incresing soil fertility, while absorbing CO². So the initial payback from increased production and quality of food, ofsets a portion of the costs, prrhaps all of the costs in situations where the right types of rocks are located near good agricultural candidate areas. The other agricultural carbon capture method is tera pretta or biochar, where organic waste is chared and mixed into soil, where it persists for many millenia, and provides a media for soil biota to live in, and reacts with varios harmfull contaminents to sequester and neutralise through chemical and biological reactions. The impilimentation of any carbon capture method is going to be dependent on local conditions, that will vary quite considerably, ie: what makes sense and is actualy benificial in one area, could easily be a net carbon cost, somewhere else. The main variables will be crushing ,trucking, and spreading costs, and then I think,actual soil ph and chemistry, as certain soil types would prevent any reaction with the rock, and atmospheric carbon. The whole thing, bieng a thing, and a deap rabbit hole wanting dedicated local expertise and knowledge. A personal observation of "carbonate beds" leads me to believe that under certain conditions, the amount of material produced is truely huge.

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