CO? Mineralization Using Reactive Species
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To address the environmental changes associated with increasing levels of atmospheric CO?, a possibility of mineralizing CO? with the species such as Ca°? and M°? ions that are already present in sea water was studied. A series of experiments conducted at temperatures in the range of 20 to 40°C showed that the activation energy for the formation of nesquehonite (MgCO?°3H?O) is 64.6 kJ/mol. It was found that the activation energy barrier can be readily overcome by simple agitation and heating at slightly elevated temperatures, e.g., 40°C. The kinetics of mineralization and the %M°? ion utilization varies depending on energy dissipation rate, temperature, pH, and NaCl concentration. The maximum M°? ion utilization achieved was 86%. Thermodynamic calculations were carried out to construct the species distribution diagrams, predict the pH of CO? mineralization, and to predict %Mg ion utilization (or extraction) from sea water. To address the issues concerning the acidification of sea water during CO? mineralization, spent solutions were treated with basic minerals such as limestone and olivine. It was found that in the presence of these minerals the pH rises to the pH of minimum solubility of the buffering mineral. The pH of minimum solubility of limestone is 8.3 and that of olivine is 8.6. Other means of pH neutralization were also discussed.
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