<p>A review article on the subject in the AGU journal <a href="http://agupubs.onlinelibrary.wiley.com/hub/journal/10.1002/(ISSN)1944-9208/" rel="nofollow noreferrer">Reviews of Geophysics</a> <a href="http://onlinelibrary.wiley.com/doi/10.1002/rog.20004/pdf" rel="nofollow noreferrer">Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification</a> 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:</p>

<blockquote>
  <p>"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."</p>
</blockquote>

<p>Also:</p>

<blockquote>
  <p>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.</p>
</blockquote>

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

CC BY-SA 3.0
2017-01-27T17:30:56.737Z
2017-01-27T17:30:56.737Z
jeffronicus
<p>As one half of the naturally occurring <a href="https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle" rel="nofollow noreferrer">Carbonate–silicate cycle</a>, carbon dioxide is naturally removed from the atmosphere by the chemical reaction:</p>

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

<p>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?</p>

CC BY-SA 3.0
2017-01-27T15:53:20.003Z
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
CC BY-SA 3.0
2017-01-27T16:02:35.593Z
@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" http://science.sciencemag.org/content/300/5626/1677
DavePhD
CC BY-SA 3.0
2017-01-28T00:21:08.443Z
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
CC BY-SA 3.0
2017-01-28T00:21:58.553Z
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
<atmosphere><climate-change><geochemistry>
What negative side effects would occur if silicate mining were used to artificially lower atmospheric CO2 concentrations?
DavePhD
# What negative side effects would occur if silicate mining were used to artificially lower atmospheric CO2 concentrations?

(Asked by: username_0 on 2017-01-27)

As one half of the naturally occurring [Carbonate–silicate cycle](https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_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?

**Tags:** atmosphere, climate-change, geochemistry

> **Comments:**
> **username_1**: 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.  
> **username_0**: @username_1 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" http://science.sciencemag.org/content/300/5626/1677  
> **username_2**: 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.  
> **username_2**: 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.  

---

## 1 answers

### Answer by username_3 on 2017-01-27. Score: 3 | Accepted answer

A review article on the subject in the AGU journal [Reviews of Geophysics](http://agupubs.onlinelibrary.wiley.com/hub/journal/10.1002/(ISSN)1944-9208/) [Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification](http://onlinelibrary.wiley.com/doi/10.1002/rog.20004/pdf) 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.


---

