(60m) Magnesium Oxide Carbonation Rate Law in Concentrated Brines

MgO is the only engineered barrier emplaced in the Waste Isolation Pilot Plant (WIPP), a U.S. DOE bedded-salt repository for transuranic waste in southeast New Mexico. MgO reduces actinide solubility by sequestering CO2 generated by the biodegradation of cellulosic, plastic, and rubber. To be an effective barrier, the rate of CO2 sequestration should be fast compared to CO2 production over the entire 10,000 year regulatory period. We are not aware of work determining the carbonation rate law in saturated brines at low PCO2 (10^-5.5 atm) in closed systems. In our experiments MgO was placed into 5m NaCl solutions and headspace PCO2 measured over time using GC/MS. Solid products were examined through XRD analysis. Results show two first order timescales in CO2 sequestration, give insight into reaction products and mechanisms, and lead towards an integrated rate equation. This method will benefit the study of kinetics of similar processes, and further understanding of the WIPP engineered barrier.

Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE AC04 94AL85000. This research is funded by WIPP programs administered by the Office of Environmental Management of the U.S Department of Energy.