Carbon Removal Technologies

Schematically:

A) H2O + CO2 H2CO3

Equilibrium favors left hand side, but water exposed to atmosphere becomes slightly acidic from right hand side.

B) Mg2SiO4 + 2 H2CO3 => 2 MgCO3 + SiO2 + 2H2O

Equilibrium strongly favors the right hand side. But the reaction is strongly kinetically hindered with naturally occurring large lumps of rock. This is why it will take a very long time for natural silicate weathering processes to absorb the extra CO2 that humans have recently added to the atmosphere.

C) CaCO3 + H2CO3 2 CaHCO3

Equilibrium favors left hand side, but limestone can be solubilized from right hand side reaction at a low rate (or faster in presence of high CO2/water concentration).

Note that the metal in the silicate of the left hand side of B can be various alkali and alkaline earth metals, but magnesium dominates in olivine.

EDIT: "CO2 Mineral Sequestration Studies in US" by Golberg et al appears to be the best reference to the thermodynamic and kinetic aspects of magnesium silicate weathering that I can easily find outside of a paywall.

https://www.osti.gov/servlets/purl/1208898

This paper is focusing on a different way to accelerate weathering: apply wet, concentrated, hot CO2 to crushed silicates. The olivine-crushing proposal discussed here on HN takes a different approach to accelerated weathering: crush and disperse larger quantities of silicates, but do not try to heat or pre-concentrate the CO2. Just let the ambient conditions of the atmosphere and oceans work on crushed rock (this is still far faster than natural weathering).

The key takeaway from this paper is on pages 3 and 4: magnesium silicate carbonation is exothermic (thermodynamically favored). Once magnesium silicate reacts with CO2, it would take more energy to undo the reaction and put that CO2 back in the atmosphere.

That is a bit optimistic :-)

The potential energy per gram of mass is much lower than for coal burning in Earth's atmosphere -- worse, the kinetics are so sluggish that you would need a very large vessel with good insulation to build up a useful temperature differential.

You'd also need to concentrate perchlorates from the Martian soil before they would sustain combustion with methane. Assuming that was done, though, perchlorates plus hydrocarbons will combust with vigor.

Taste can often be regarded as ephemeral, while fast fattened livestock can be discerned to taste different and are considered inferior in most food celebrating cultures.

There is a possible health factor involved with grass fed (or mixed prairie for better) beef and dairy accumulating a markedly different spectrum of omega oils, which are debated inconclusively, but also formally studied and theorized to be superior for human consumption.

A focus on the strength of methane emissions seems increasingly common in discussions and magazine articles, while the long developed advice from the IPCC is that CO2 demands priority because methane clears naturally in a decade or so, and requires less action to avoid than CO2 output which takes much longer to clear.

My understanding of IPCCs focus on CO2, is that while methane reduction presents an opportunity to buy a few years time, the priority is to convince action on the hardest problem which has been created, is worsening rapidly and much harder to clear.

If you are interested in modeling rate constants and mechanisms, the most interesting work I have come across is the Reaction Mechanism Generator developed at MIT and Northeastern University:

https://github.com/ReactionMechanismGenerator

https://greengroup.mit.edu/reaction-mechanism-generator

https://rmg.mit.edu/

https://web.northeastern.edu/comocheng/

As you may be aware, determining rate constants from calculations is quite difficult even for gas-phase reactions. It's much harder for condensed-phase reactions. I do not have any hope of applying these techniques to olivine weathering at present. There have been quite a few small scale laboratory experiments on olivine weathering. There will be more factors at work in a real near-shore environment: abrasion by sand and wave action, biological activity, varying temperatures depending on the locale. I think that questions of rates need to be answered by field trials now; theory is inadequate and small lab experiments have already been done. But I still contend that this is not "simply dissolving" CO2 in ocean surface waters -- it is an acid-base reaction, with magnesium providing alkalinity.

Giving What We Can has published an analysis on the topic. You can read it here when the site is up again (it is down for me right now): https://www.givingwhatwecan.org/research/causes/climate-chan...

Tl;dr: Cool Earth is their recommendation.