Comment Re:Turning CO2 into what? (Score 2) 142
From the US DOE :
"Direct mineral carbonation has been investigated as a process to convert gaseous CO2 into a geologically
stable, solid final form. The process utilizes a solution of sodium bicarbonate (NaHCO3), sodium chloride
(NaCl), and water, mixed with a mineral reactant, such as olivine (Mg 2SiO4) or serpentine [Mg 3Si 2O 5(OH)4].
Carbon dioxide is dissolved into this slurry, by diffusion through the surface and gas dispersion within the
aqueous phase. The process includes dissolution of the mineral and precipitation of magnesium carbonate
(MgCO3) in a single unit operation. Optimum results have been achieved using heat pretreated serpentine
feed material, with a surface area of roughly 19 m 2 per gram, and high partial pressure of CO2 (PCO2).
Specific conditions include: 155C; PCO2=185 atm; 15% solids. Under these conditions, 78% stoichiometric
conversion of the silicate to the carbonate was achieved in 30 minutes. Studies suggest that the mineral
dissolution rate is primarily surface controlled, while the carbonate precipitation rate is primarily dependent on
the bicarbonate concentration of the slurry. Current studies include further examination of the reaction
pathways, and an evaluation of the resource potential for the magnesium silicate reactant, particularly olivine.
Additional studies include the examination of various pretreatment options, the development of a continuous
flow reactor, and an evaluation of the economic feasibility of the process.
"