Emulation of ambient carbon dioxide diffusion and carbonation within nickel mining residues

The dynamic evolution of CO2 sequestration using nickel mining residue (NiMR) was studied using a specially-designed dual-compartment differential fixed-bed diffusion–carbonation cell. Reactivity of NiMR material in terms of carbonation uptake was monitored as a function of time, initial CO2 composition and liquid saturation. Dynamic tests exposed a positive correlation between CO2 breakthrough time across the NiMR layer and liquid saturation. Low carbonation rates were observed under both dry and completely saturated conditions. The latter suffered from slow CO2 diffusion in water whereas the former, despite the facilitated transport of gaseous CO2 across NiMR samples, lacked a sufficient supply of leached magnesium and dissolved CO2. However, the CO2 uptake was substantially stimulated when partially saturated NiMR layers were carbonated. The carbonation kinetics was rationalized in terms of reaction medium and CO2 dissolved species. Under partially saturated conditions, rapid gaseous CO2 diffusion and dissolution in interstitial water along with leaching of magnesium were key processes in carbonation.