Nanoscale Interfacial Reactivity in Tamarack Peridotite: Insights for In Situ Critical Mineral Recovery

The Tamarack ultramafic intrusion in Minnesota, USA, may be suited to host concurrent CO2 injection and critical mineral recovery. These dual capabilities are vital to manage emissions and supply metals (e.g., nickel) necessary for rapidly upscaling energy and data technologies. To understand subsurface carbonation reaction pathways and assess mineralization potential in the Tamarack Intrusive Complex (TIC), we reacted a suite of Tamarack Bowl intrusion olivine (BIO) samples with aqueous-dissolved and liquid or supercritical CO2 (scCO2) at 90 bar and 21–90 °C. Samples were characterized pre- and postreaction with multiple geochemical and mineralogical techniques, and results indicate mineral dissolution followed by magnesite precipitation. Pseudo in situ Identical Location Transmission Electron Microscopy (IL-TEM) experiments revealed that a carbonation reaction of TIC BIO peridotite with water-saturated scCO2 formed aragonite nanocrystals on an altered plagioclase surface and induced dissolution of nickel-bearing forsteritic olivine. The presence of nanoscale-resolved carbonation products identified by IL-TEM, coupled with carbonate transformation rates quantified in batch reactions, suggests that the TIC BIO resource can conservatively store 320–1,070 million metric tonnes (MMT) of CO2 via mineralization while mobilizing 0.9–3.1 MMT of nickel if only 5% of the TIC rock volume is accessed.