--- In http://tech.groups.yahoo.com/group/Know_Nukes/message/20978
"Stewart Peterson" <issues@...> wrote:

> 110% is a fairly precise and very large number--
> could you back that up with (a) how much silicate
> it would take per ton of CO2, (b) a reasonable assurance
> that there is enough material to do what you say
> is needed for the amount of time you say it will be
> necessary (remember, if this is a long-term effort
> to neutralize continued fossil fuel emissions,
> you're going to need to neutralize those emissions
> more than once),
> (c) how long it would take, and (d) why there wouldn't
> be any other adverse environmental impacts
> from this silicate dispersal? Generally when you spray
> things into the environment, something happens, somewhere,
> to something.

Section 7.2 of
http://arch.rivm.nl/env/int/ipcc/pages_media/SRCCS-final/
IPCCSpecialReportonCarbondioxideCaptureandStorage.htm
(http://preview.tinyurl.com/2bc7m2 ) deals with your points
'a' and 'b'.

It "deals ... with so-called mineral carbonation, where high
concentration CO2 from a capture step (see Chapter 3)
is brought into contact with metal oxide bearing materials
with the purpose of fixing the CO2 as carbonates".

It does not address intentionally causing
atmospherically dilute CO2 to contact the materials outdoors,
and this, I think, is an oversight.
They justify it with these words in section 7.2.2:

"Even at the low partial pressure of atmospheric CO2
and at ambient temperature, carbonation of metal oxide
bearing minerals occurs spontaneously, though on geological
time scales ...

Limitations arise from the formation of silica or carbonate
layers on the mineral surface during carbonation that tend
to hinder further reaction ..."

Also known as "passivation".
As previously said, experience with mine tailings
is showing us, in answer to your 'c', that the particular
geological time scale in question is, as I suspected but did
not know in February, years to tens of years.

We need only increase the surface area to defeat the passivation,
and the energy required to do that, I calculated at
http://www.realclimate.org/index.php/archives/2007/02/save-the-world-earn-25-mil\
lion/#comment-26336
.

If we believe extra CO2 in the atmosphere is doing harm,
it's not reasonable to require, as you do in 'd', that
"there wouldn't be any other adverse environmental impacts",
just that they be small compared to the harm of leaving
the CO2 up.

That harm doesn't have to be much for large amounts of
MgCO3 and SiO2, or CaCO3 and SiO2, to be less harmful still.
Section 7.2.5:

magnesium carbonate and silica may find uses
as soil enhancers, roadfill or filler for mining operations.
Eventually mineral carbonation would have to operate at
scales that would saturate any product or byproduct market ...

A few hundred km^3 dispersed over tens of millions of km^2
of desert, or hundreds of millions of km^2 of ocean,
would be unobtrusive. It would be enough soil enhancer
to make a 1-cm layer, if unmixed -- although it could not
remain unmixed, because it would precipitate over a period
of years -- or a 1-mm-deep layer on the ocean, again, if unmixed.

Similarly, in a remedial effort to make harmless 100 or 200
gigatonnes of past CO2 emissions, it's OK to put in more
energy than was initially gained by emitting them;
but as it turns out, the extra energy required is only 14
percent, if the original emission was from burning pure carbon.


--- G.R.L. Cowan, hydrogen-to-boron convert
How shall the car gain nuclear cachet?
http://www.eagle.ca/~gcowan/boron_blast.html