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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.

Investigation of the CO&lt;sub&gt;2&lt;/sub&gt; Sequestration by Indirect Aqueous Carbonation of Waste Cement

Investigation of the CO<sub>2</sub> Sequestration by Indirect Aqueous Carbonation of Waste Cement