Influence of physicochemical properties of Brazilian serpentinites on the leaching process for indirect CO2 mineral carbonation

pH-swing mineral carbonation is kinetically favorable and requires a short reaction time. It must also obtain a high extraction rate for reactive elements in the leaching process. The main purpose of this study is to investigate the behavior of different serpentinite rocks in the leaching processes; the reactivity of Brazilian serpentinite rocks (such as: S-GO and S-MG) is analyzed based on physicochemical properties in order to understand their relationship to leaching efficiency. Surface area-to-volume ratio (SBET/Vp) and metals-to-silicon ratio (Σ(Mg, Ca)/Si) were used to measure reactivity. Leaching was carried out to determine Mg and Fe extraction. Reaction conditions for both serpentinite rocks were: 355-250 μm particle size, 4 M HCl concentration, 100 °C, and 2 h of reaction time. Characterization results show that both serpentinite rocks (S-GO and S-MG) have high magnesium (Mg) content. SBET/Vp was 36 for S-GO and 29 for S-MG, while Σ(Mg, Ca)/Si was 2.64 for S-GO and 1.20 for S-MG. These results suggest that S-GO is approximately 50% more reactive than S-MG, and that S-MG is limited by low accessible surface (SBET/Vp) and the high mineralogical complexity (Σ(Mg, Ca)/Si). Leaching results confirmed the reactivity; Mg and Fe extraction from S-GO was 94 ± 1%. However, results for S-MG were 34% for Mg and 60% for Fe. In order to increase the reactivity of S-MG, particle size was reduced to 75-63 μm. Even though S-MG was mechanically activated, Mg and Fe extraction has not increased significantly.