Reactive pathways of synthetic forsterite and Mg/Ni-serpentine: Insights into incipient dissolution and carbonation

Carbon capture, utilisation and storage is among the key strategies to mitigate the increasing concentration of atmospheric carbon dioxide. Mineral carbonation stands out as a promising solution for long-term carbon sequestration by exploiting Ca–Mg-bearing oxides, hydroxides, and silicate minerals such as olivine and serpentine. Although the reaction occurs spontaneously in nature, it is strongly hindered by mineralogical and structural factors. In this study, nanocrystalline pure forsterite and Mg- and Ni-endmember serpentines were synthesised as model phases to disentangle the role of composition, crystal structure, and morphology in incipient dissolution and carbonation and to maximise reactivity through increased surface-to-volume ratios. The choice of Ni-serpentine endmember aims to investigate the fate of Ni after dissolution and carbonation, considering that in nature serpentine can incorporate up to 0.5 wt% of nickel oxide. A systematic experimental strategy was designed to investigate their early-stage dissolution and carbonation behaviour under mild hydrothermal conditions (100 °C, pCO2 ≤ 6 bar), using microwave-assisted treatments in a controlled environment. The products were thoroughly characterised, both as solid precipitates and aqueous components, through X-ray Powder Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, micro-Raman and Inductively Coupled Plasma – Optical Emission Spectroscopy. This direct, parallel comparison reveals distinct behaviours among the tested materials, with forsterite and Mg-serpentine releasing Mg into solution and promoting the formation of hydrated Mg-carbonates, whereas Ni-serpentine nanocrystals remain largely inert, immobilising Ni within their structure. These findings have potential implications not only for carbon dioxide sequestration but also for critical metal recovery processes.