Sulfide Transport through Nanochannels in Carbonates Enables Simultaneous Cobalt Extraction and Carbon Mineralization

During the mineralization of CO 2 with alkaline metal feedstocks, various carbonate minerals can form. In particular, when magnesium or calcium carbonates (MgCO 3 or CaCO 3 ) form, critical elements, such as cobalt (Co), can be incorporated into these carbonate structures. Effectively recovering these critical elements from the mixed phases is essential, while also minimizing disruption to the host MgCO 3 or CaCO 3 solid phase to ensure durable carbonstorage. Our proof-of-concept approach combines carbonation, sulfidation and subsequent oxidation to efficiently extract Co. In this study, aqueous solution and solid silicates containing Co and Mg undergo carbonation reactions. Then, sulfidation treatment transforms cobalt carbonates into sulfides, with a conversion efficiency exceeding 95%, while over 92% of the MgCO 3 solid remains stable. High-resolution transmission electron microscopy reveals that MgCO 3 shells form nanochannel-like pore structures (called “nanochannel”) and cobalt sulfide nanoparticles nucleate inside these nanochannels. Through nanochannels, sulfide ions can effectively transport to the core, fully converting cobalt carbonates to cobalt sulfides. When hydrogen peroxide is introduced, cobalt sulfides are oxidatively dissolved into aqueous cobalt and sulfate ions while maintaining MgCO 3 solids as valuable products. This novel process achieves effective critical element recovery alongside concurrent carbon storage, which supports the sustainable development of resources and byproduct treatment from energy generation.