Nickel mobilization during single-stage aqueous mineral carbonation of serpentinized peridotite at 185 °C and PCO₂ of 100 bar

Forsterite-rich ultramafic rocks, such as serpentinized peridotites, are considered highly promising natural materials for mineral carbonation – a carbon capture and storage (CCS) technique aimed at reducing atmospheric carbon dioxide (CO₂) by sequestering carbon as carbonate minerals. These rocks are commonly characterized by a high content of divalent cations, including nickel (Ni^2 +), whose behavior and mobility during mineral carbonation remain insufficiently understood. This issue is critical, as the large-scale application of mineral carbonation may pose ecotoxicological risks by mobilizing specific metallic elements naturally occurring in ultramafic rocks. To elucidate possible Ni mobility during single-stage aqueous mineral carbonation, 15 g of powdered serpentinized peridotite was carbonated in a batch-type reactor for 96 hours at 185°C and a P_CO₂ of 100 bar. The experiment resulted in the dissolution of forsterite and the extensive crystallization of magnesite, demonstrating that the serpentinized peridotite is a highly effective natural material for permanent CO₂ storage in the single-stage carbonation processes. Nickel released during the dissolution of forsterite (approximately 50 % of the whole Ni budget) was mainly incorporated in newly formed Ni-rich phyllosilicates (more than 98 %) and a small portion was mobilized into the post-carbonation fluid (less than 2 %), reaching a concentration of approximately18 mg/kg after 96 hours. The presence of Ni in newly crystallized magnesite crystals has not been detected. These results suggest that the behavior of Ni during single-stage mineral carbonation is complex and requires careful monitoring to prevent potential negative impacts on the natural environment.