Permaculture: How does rock dust help in the removal of CO2 from the atmosphere?

Question

How does rock dust help in removal of CO2 from the atmosphere?

I want to know because rock dust is supposed to provide vital elements to crops and improve productivity. So how does it do it? What are the advantages/disadvantages?

Thanks for the great answers. A bit more of an understanding has enabled me to do better Internet searches.

Will post links as I find in case anyone is interested.

Re mineralization
http://66.102.1.104/scholar?hl=en&lr=&q=cache:gZckVSLGBRMJ:www.soilandhealth.org/01aglibrary/010146tsoc.pdf+remineralization+CO2+rock+dust#87
http://scholar.google.com/scholar?q=permaculture%20rock%20dust&hl=en&ie=UTF-8&oe=UTF-8&um=1&sa=N&tab=ws
http://www.menofthetrees.com.au/RockDust.pdf
http://forums.permaculture.org.au/archive/o_t__t_750__start_15__index.html
http://lists.ibiblio.org/pipermail/permaculture/2000-May/011172.html

http://www.remineralize.org/climate.php

Answer 1

Rock dust only works on atmospheric CO2 indirectly.
I have always been a huge fan of mined minerals (rock dusts) as soil amendments. Life on earth, especially the basic bottom of the food chain, the plants, have evolved to take advantage of the niche that is our soil. The basic parent material of that soil, ground rock from our planets crust, is the result of all the different weathering processes, and the subsequent organic additions of the generations of plants, the animals that feed off them, and the micro-organisms that are the living and working conversion component, make up that soil. It is dynamic and, next to the ocean, one of the largest components in the many cycles that are the complex chemistry's of our environment. It is only natural and common sense to use rock dusts in the environment, not only for agriculture, but to help in the repair, where possible, of environmental issues. The article sited by the first answer to this question was very good at explaining the larger picture that the soil, the land, and the parent material play in the Carbon cycle. In my opinion it was not a very realistic goal, though, to expect to dust every usable acre on the planet with two or three tons of dust every year. Even with the increased activity of plants from the use of these dusts and the reduction of 50% to, let's say, one to one and a half tons per acre, it is still an impossible goal.

Even if one were to reduce rock dust to the consistancy of baby powder it would have little effect in the atmosphere from just the standpoint of chemistry alone. I wish it were not so as we could provide a quick fix. As the article sited above states, if enough was spread threw the environment, it would have the effect we need. Most of the CO2 in the whole of the planets environment is dissolved in the oceans water. I would expect that putting huge amounts of iron based rock material in the water would help some by fertilizing algae and that way incorporating some of the dissolved CO2. It is my understanding though that in experiments, most material added quickly passes into an unusable zone away from the light and algae. Statistics I have read claim that as much as 1/3 of the carbon in the ocean is from human sources so by finding ways to limit our carbon in the cycle, it would allow the oceans to pick up more of the CO2 from the atmosphere. Most of that is chemical in nature and the biological component of CO2 removal (like algae) is a tiny fraction of the total.

So back to how rock dust would help remove atmospheric CO2. The effect will only be indirect and will have to come from as many directions as we can imagine and implement. From an agricultural standpoint, and that is at a level from the largest agricultural corporations to the smallest home hobby garden, using mined mineral ammendments should be a natural matter of course; they are natural, available locally, and provide some of both the major and minor elements used up or lost as the soil ages or are removed from repeated crop harvests. Obviously not all. But in this way rock dust helps to remove CO2 from the air by feeding plants and soil organisms, and providing some chemical activity to help in binding the carbon. By keeping that carbon from the CO2 in the plants, and then in the soil locked up and mineralized in humus and like structures, rock dust helps in a round about indirect way. The added effect of no-till farming, cover cropping, crop rotation, and good solid mulching in addition to the use of rock dusts and mined mineral ammendments are the best ways to keep carbon sequestered; locked up minerally and put to good use as a soil component. Unfortunately it is only practiced on an average of one acre in twenty here in the United States. By using rock dusts on pastureland with good management of grazing one can sequester even more carbon in the soil.

As to disadvantages, it is somewhat slower than chemical so it needs to be finely divided to work well and that requires energy. It is heavy and movement needs to be limited to local use or the penalty of cost to ship and energy use and subsequent pollution involved diminishes it's value and effect.

Answer 2

My initial guess was that there were one of two ways, the first is chemical (see link below) and the second biological, in that by fertilizing the land you get more plants turning CO2 into plants and taking it out of the atmosphere. But I don't think either is practical, and only the first makes sense from a chemical perspective since more fertilization is going to release a lot of N2O, which is an even more potent greenhouse gas than CO2.

What the guy says in the link below about weathering of rock and uptake of CO2 is true, but largescale mining and grinding of rock, not to mention transporting it, spreading it on fields, etc., is an energy intensive operation. I suspect that you would produce more CO2 in producing the rock dust than you would remove from the atmosphere through the chemical weathering or biological uptake. In addition, deposition of acidic rainwater on the rock would release all the chemically sequestered CO2, so it isn't clear the powdered rock idea really would work in the long term. Finally, spreading that much rock on the soil is also going to add a lot of salt and change soil pH dramatically, and that is in general a bad thing for agriculture. Just ask the Anasazi about long-term effects of salt on agriculture.

Overall, it is a phenomenally silly idea. There are no workable geo-engineering solutions to anthropogenic production of CO2. The answers lie in social engineering in reducing total energy use and technological advancement in improving the efficiency of energy production in terms of kW-hr per ton CO2 produced.

Addendum: There is another reason why this is a kinda dumb idea in terms of CO2 sequestration and that is that you can't get CaO or MgO to take up CO2 without first hydrating the alkali earth oxides. So in addition to adding the several tons of rock dust each year, you're going to have to flood the fields. The hydration also takes a while. So every year, another few billion tons of rock dust, and lots of freshwater.

Answer 3

I would guess that it is chemically and depends on the composition of the "rock dust" used. It might be physical (what is the right word ... not nanotechnology); i.e. the CO2 molecules stick to the surface of the dust electrostatically.

Either way it is basically salting the clouds by the sounds of it.

The link given above explains it, but I think the people involved with that site and the movie etc are a bunch of whack jobs. Total BS.