(512u) 29si Solid State MAS NMR Study on Leaching Behaviors of Mg-Bearing Silicate Structures for CO­2 Mineralization

Understanding fate and chemistries of different silicate structures in minerals are important research aims for carbon mineralization, where captured CO₂ is converted to a thermodynamically stable solid carbonate phase. In this study, ²⁹Si MAS NMR and XRPD analysis were applied to investigate the fate of different silicate structures (Q⁰ – Q⁴) in heat-treated Mg-bearing mineral (serpentine) when they were exposed to a CO₂-water system (carbonic acid). It was able to explain complicate silicate structures of heat-treated serpentine minerals and its dissolution mechanisms with the identified silicate structures. While natural serpentine mineral (untreated) has a single crystalline Q³ silicate structure, the heat-treated serpentine was identified as a mixture of amorphous (Q¹: dehydroxylate I, Q²: enstatite, Q⁴: silica) and crystalline (Q⁰: forsterite, Q³: dehydroxylate II and serpentine) silicate structures. The heat-treated serpentine leaching experiments showed that both Mg and Si in the amorphous silicate structures (Q¹: dehydroxylate I, Q²: enstatite) are more soluble than those in crystalline phase (Q⁰: forsterite, Q³: dehydroxylate II and serpentine), indicating that the amorphous phases play important roles in the high reactivity of the heat-treated serpentine minerals. Then, the solubilities of different silicate structures in the heat-treated serpentine were qualitatively evaluated and they were in the order of Q¹ (dehydroxylate I) > Q² (enstatite) >> Q⁰ (forsterite) > Q³ (dehydroxylate II) > Q³ (serpentine). Thus, tuning the natural serpentine silicate structure (Q³) towards Q¹ and Q² phases should be maximized during the heat treatment process and it would significantly improve carbon sequestration potential of serpentine minerals.