Selective Extraction of Nickel and Cobalt from Serpentine Minerals Using Carbon-Negative Carbonation-Assisted Leaching Technology

Serpentine is a group of hydrous magnesium–iron phyllosilicate minerals that contain both nickel (Ni) and cobalt (Co). To date, the extraction of both Ni and Co from nickel-bearing serpentine minerals has been technologically challenging and economically unviable. In this work, a carbon-negative leaching technology was developed to extract Ni and Co from serpentine-rich rocks while simultaneously sequestering CO₂ in the form of carbonate minerals. The conversion of serpentine to olivine using thermal activation was investigated under air and hydrogen environments. Lab-scale carbonation-assisted leaching trials showed that the hydrogen dehydroxylation process effectively transformed serpentine to olivine, increased the porosity of the feed minerals, and thereby enhanced the mineral carbonation efficiency. The carbonation efficiency reached 86%, with Ni and Co extraction rates of 80% and 75%, respectively, after 2 h. The carbonation efficiency was found to correlate strongly with the metal extraction efficiency, indicating that the limiting factor was the dissolution and release of divalent ions from the silicate mineral. Under optimal conditions, the activated serpentine mineral exhibited a CO₂ uptake capacity of 357 kg per ton of feed, with approximately 2.63 kg of nickel and 0.43 kg of cobalt recoverable per ton of the feed. These findings illustrate the viability of hydrogen dehydroxylation coupled with carbonation-assisted leaching technology to unlock critical minerals from unconventional low-grade nickel ore resources.