Kinetic evaluation of the CO₂ sequestration process of MgO-rich materials derived from ferronickel slag

Ferronickel (FeNi) slag can be used to sequestrate CO₂ by performing an alkaline pretreatment process using NaOH to obtain porous MgO-rich materials (MgO obtained from FeNi slag, MgO-FS). CO₂ is mineralized by porous MgO-FS in the form of MgCO₃. This study aimed to investigate the overall carbonation reaction kinetics of porous MgO-FS. The carbonation process was performed in an autoclave reactor under controlled CO₂ pressure by continuously supplying CO₂ throughout the experiment. The carbonation reaction kinetics of MgO-FS were investigated by varying the CO₂ partial pressure (3–12 bar) and reaction temperature (120–150 °C). The surface coverage model fitted the experimental data well. This means that the carbonation product (MgCO₃) was continuously deposited on the surface of the particles. The MgCO₃ crystals formed on the particle surface were clearly observed by scanning electron microscopy. The diffusion in the MgCO₃ surface covering the MgO-FS particles is the rate-controlling step, preventing the contact and diffusion between the solution and the free surface of the particles. By stirring at 500 rpm, both the maximum degree of carbonation and overall reaction rate significantly improved because stirring reduces the formation of large particle agglomerates. Under the conditions of 150 °C, CO₂ partial pressure of 12 bar, duration of 1 h, and liquid/solid ratio of 10 mL/g without stirring, the degree of carbonation and overall reaction rate constant were only 51.1% and 0.48 × 10⁻⁶ mol s⁻¹ m⁻², but they increased to 73.3% and 2.25 × 10⁻⁶ mol s⁻¹ m⁻² by stirring at 500 rpm.