(290f) Evaluating the Viability of CO2 Mineralization Via Reaction of Caustic Waste Materials

Consensus in the scientific community is that anthropogenic greenhouse gas (GHG) emissions are a dominant factor contributing to global climate change.  While CO₂ is not the strongest greenhouse gas with respect to radiative forcing, it is, by far, the largest volume GHG, and is recognized by most researchers to be the greatest contributor to observed increases in mean atmospheric temperatures.  As such, separation of anthropogenic CO₂ from coal fired power plants and other large industrial sources, and storage of that CO₂ out of the atmosphere has been proposed as a means to slow the rise of, and possibly stabilize atmospheric concentrations of CO₂.  Proposed sinks for anthropogenic CO₂ include storage in geologic formations (saline formations, coal seams, depleted oil- and gas-bearing formations, basalts, and organic-rich shales), uptake of CO₂ into plants with terrestrial storage in soil and biomass, and reaction of CO₂ex situ with naturally occurring minerals or byproduct streams from industrial processes.   

Reacting CO₂ with caustic industrial byproduct streams (solids, slurries, or solutions) has been proposed by many as a possible viable approach for ex situ CO₂ sequestration.  Cited advantages of this paradigm include proximity (often co-location) of CO₂-bearing industrial byproduct gas streams to caustic byproduct materials, possibility of reacting whole flue gas streams with caustic byproduct – thereby obviating CO₂ separation from mixed byproduct gas streams, concomitant neutralization of caustic waste materials that would otherwise need to be neutralized with acidic reagents, ability to realize significant reaction efficiency at very modest reaction conditions, storage of anthropogenic CO₂ in a stable mineralized form, and potential to generate a saleable coproduct mineral carbonate stream.  Acknowledged disadvantages of this CO2 storage paradigm include:  relatively low CO₂ storage capacity of global caustic industrial byproduct streams as compared to global anthropogenic CO₂ emissions, need to handle large volumes of reactant and product materials, potential to mobilize heavy metals and other trace constituents of concern, and potential for mineralized CO₂ to react and release stored CO₂ under certain environmental conditions.  Taken together, these suggest that CO₂ mineralization using caustic byproduct materials may be a viable approach to partially offset CO₂ emissions for select industries and at specific facilities, but may not make a significant contribution toward stabilizing atmospheric CO₂ concentrations.

Given this context, select proposed approaches for CO₂ mineralization with caustic materials will be considered.  Discussion will include summary of experimental efforts to evaluate reactivity of CO₂ with coal utilization byproducts and bauxite residue materials, consideration of the applicability of geochemical equilibrium modeling to estimate CO₂ mineralization potential, and discussion of possible implications for viability of this CO₂ storage paradigm.