Author(s)

Myoungwook Mun^*, Heechan Cho, Jihoe Kwon, Kihong Kim, Rina Kim

Department of Energy Resources Engineering, Seoul National University, Seoul, Republic of Korea.

Mineral carbonation of CO₂ with fine-grained waste cement was investigated using NH₄Cl as a recyclable extracting agent. The amount of calcium extracted with NH₄Cl was not as high as with more commonly used extraction agents such as HCl and CH₃COOH. NH₄Cl also exhibited high selectivity in the calcium extraction process, such that calcium ions comprised over 99% of the leaching solution. Another positive benefit of using NH₄Cl was that precipitation of calcium carbonate by CO₂ injection was possible without the addition of basic reagents. Moreover, the NH₄Cl regenerated during carbonation can be reused for calcium extraction. However, test results using regenerated NH₄Cl solution in a cyclic fashion revealed that the process was not perfectly cyclic, but rather the calcium amount after precipitation increased as the cycle proceeded. The geochemical computer simulation PHREEQC was utilized to gain better insight into the cyclic mineral carbonation processes using NH₄Cl solution. The simulation was based on thermodynamic equilibrium so that the amount of Ca in the solution fluctuated between specific values in a periodic fashion, unlike the experimental results of calcium accumulation in the extraction solution. One reason for this phenomenon was the kinetic/thermodynamic balance controlled by the amount of Ca²⁺ and CO₂ present in the solution. However, it was feasible to use a geochemical model to evaluate the mineral carbonation process with the correction factors since the deviation between the experimental and the simulation results remained fairly constant throughout the cycle.

CO₂ Sequestration, Mineral Carbonation, Waste Cement, Ammonium Chloride, PHREEQC

Mun, M. , Cho, H. , Kwon, J. , Kim, K. and Kim, R. (2017) Investigation of the CO₂ Sequestration by Indirect Aqueous Carbonation of Waste Cement. American Journal of Climate Change, 6, 132-150. doi: 10.4236/ajcc.2017.61008.