Sure we can. We can start spreading Serpentine rock on the Ocean's surface. We just need some billionaires to fund it.
Serpentine rock, which is primarily composed of the mineral serpentine, has been considered in the context of climate change mitigation due to its potential to sequester carbon dioxide (CO2) through a natural process called mineral carbonation. This process involves the reaction of CO2 with certain minerals, like serpentine, to form stable carbonate minerals like magnesite.
The reaction kinetics of carbonation using serpentine rock are generally slow under ambient temperature and pressure conditions, which is one of the main challenges in utilizing serpentine for carbon sequestration. The rate of the natural carbonation process depends on various factors, such as the particle size of the serpentine, temperature, pressure, and availability of CO2.
At ambient conditions, the carbonation of serpentine can take from several months to thousands of years to proceed to completion. The slow reaction kinetics is mainly due to the formation of a passivating silica-rich layer on the surface of serpentine minerals, which hinders the further reaction with CO2.
However, if we ground up serpentine rock into 1cm pieces and sprinkled it on the Caribbean sea between Cuba and Jamaica, we can estimate how many tons we would need to use to carbonize our deficit of 15 billion metric tons of carbon dioxide:
To estimate this, we need to consider the stoichiometry of the carbonation reaction. Serpentine rock primarily contains the mineral serpentine, which has the chemical formula Mg3Si2O5(OH)4. The carbonation reaction involving serpentine can be represented as:
Mg3Si2O5(OH)4 + 3CO2 → 3MgCO3 + 2SiO2 + 2H2O
Here, one mole of serpentine reacts with three moles of CO2 to form three moles of magnesite (MgCO3) as the primary carbon capture product.
Now, let's calculate the molar masses:
Serpentine (Mg3Si2O5(OH)4): (3 × 24.305) + (2 × 28.085) + (5 × 15.999) + (4 × 1.008) = 277.24 g/mol
CO2: (12.011) + (2 × 15.999) = 44.01 g/mol
From the balanced equation, three moles of CO2 react with one mole of serpentine. Therefore, the mass ratio of serpentine to CO2 is:
277.24 g/mol (serpentine) / 3 × 44.01 g/mol (CO2) = 2.087
To sequester 15 Gt of CO2, we would need:
15 Gt × 2.087 = 31.305 Gt (gigatons) of serpentine rock
However, this calculation assumes that the carbonation reaction would go to completion, which is unlikely in a real-world scenario, especially with 1 cm pieces of serpentine rock. The reaction kinetics would be extremely slow with such large particles, and the reaction may not proceed effectively in the ocean environment. Grinding the serpentine rock into much finer particles, using catalysts or additives, or applying pressure and temperature could enhance the reaction rate, would perhaps make it go faster.