# What negative side effects would occur if silicate mining were used to artificially lower atmospheric CO2 concentrations?

As one half of the naturally occurring Carbonate–silicate cycle, carbon dioxide is naturally removed from the atmosphere by the chemical reaction:

CaSiO$_3$ + 2CO$_2$ + H$_2$O → Ca2+(aq) + 2HCO$_3$-(aq) + SiO$_2$

What would be the side effects of artificially enhancing this process by mining large amounts (on the order of 10 times world coal production) of silicate bearing rocks to reverse man-made climate change?

• Uh, NO. Most geoengineering ideas are bad. This one is beyond bad. Ten times the problems with mining tailings, ten times the problem with acidification of waterways, ten times ... And then it probably won't work. Most of the carbon captured by weathering is released back to the atmosphere in short order. Only a small fraction is sequestered. I would expect 10X problems in many regards, and essentially zero reduction in CO2. – David Hammen Jan 27 '17 at 15:53
• @DavidHammen The journal Science says "A better option than forming water-soluble bicarbonates would be the formation of insoluble carbonates that could be stored at the location of the mineral base, confining environmental impact to a specific site. To this end, serpentine or olivine rocks rich in magnesium silicates can be mined, crushed, milled, and reacted with CO2. Estimated mining and mineral preparation costs of less than \$10 per ton of CO2 seem acceptable" science.sciencemag.org/content/300/5626/1677 – DavePhD Jan 27 '17 at 16:02
• We had a guest speaker lately saying that they looked at what happened in old mines in ultramafic rocks. The rocks are already crushed and milled and are just sitting there, so it was a good opportunity to see what happens over the time scale of tens of years. They formed a carbonate crust on top, and as you went in deeper, you had less and less carbonate. Even in the carbonate crust, there wasn't 100% carbonate. So you will have to re-crush and re-mill it every few years to keep the reaction going. – Gimelist Jan 28 '17 at 0:21
• Another point was that there is simply not enough. Even if you took all old mines and reacted them to 100% carbonate, it wouldn't even make a dent in the global CO2 budget. – Gimelist Jan 28 '17 at 0:21

A review article on the subject in the AGU journal Reviews of Geophysics Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification by Hartmann, et.al. (2013) notes many uncertainties that would need to be researched and quantified to evaluate both the potential effectiveness as well as the drawbacks of the process, known as Enhanced Weathering:

"The potential negative environmental impact of Enhanced Weathering is also important to consider and investigate further. Application of rock powder to the land surface might increase the concentration of airborne dust in the local environment. The potential risk to human and animal health may limit the appropriate application sites (away from human centres or sensitive ecosystems) or the severity of comminution, depending on the techniques applied. This in turn will limit the efficacy and effectiveness of Enhanced Weathering. The mobilization of potentially toxic elements contained in some silicate rocks may detrimentally effect primary production and/or accumulate in the food chain, both of which could be harmful to human populations. Therefore an assessment of usable rocks and their locations is needed."

Also:

To sequester a significant amount of carbon dioxide from the atmosphere, an Enhanced Weathering program would need to process 1Gt to 10 s of Gt of rock per year. This would make it one of the largest global industries.

That alone would create economic and social impacts, as well as additional carbon emissions that would need to be offset.