Artificial Laterite from Acid Leaching of Ultramafic Rocks: Mobilization, Enrichment, and Extraction of Critical Metals

Natural weathering of ultramafic rocks produces laterites that host nickel (Ni) and cobalt (Co) which are critical to a renewable energy transition. Here, we performed sulfuric acid leaching on an ultramafic rock, which produces an iron (Fe)-rich residue that concentrates Ni and Co on laboratory time scales, herein termed artificial laterite. Nickel and Co in the artificial laterite are up to 5 - 7 times enriched relative to the raw material and close to their cutoff grades of natural laterite ores. The most Ni-and Co-rich artificial laterite is dominated by poorly crystalline ferrihydrite as revealed by synchrotron-based powder diffraction (PD) and X-ray absorption spectroscopy (XAS, Fe K-edge). By reacting this artificial laterite with aqueous Fe(II) at circumneutral pH and ambient temperature, release of structurally bound Ni and Co is markedly enhanced. Followed by mild acid extraction, total recovery of Ni and Co is around 80%. Meanwhile, impurities such as coprecipitated silica with ferrihydrite would not negatively impact metal release. Our work demonstrates that acid leaching of ultramafic source rocks can generate artificial laterites that are more reactive than their natural counterparts. Furthermore, leaching of these rocks releases magnesium (Mg), an important cation for carbon mineralization, potentially offsetting carbon emissions during metal extraction.