PNNL

The Science

Demand for cobalt (Co) has surged due to its increased use in metal superalloys and cathodes for rechargeable batteries. Mafic and ultramafic rocks are low-grade Co ores, yet are abundant and have high durable CO₂ storage potential. Researchers investigated the impact and fate of Co during metal silicate carbonation under low water, humidified CO₂ conditions. The results show that Co-doped forsterite ((Mg,Co)₂SiO₄) carbonated to Co-rich magnesite ((Mg,Co)CO₃), but the rates of carbonation were an order of magnitude slower than for pure forsterite at similar conditions. 

The Impact

Carbonation could improve the economic viability of Co extraction from mafic or ultramafic rocks by both lowering processing costs and helping the mining industry reach net-zero CO₂ emissions. A low-water approach has the potential to reduce water usage, decrease waste, and favor the most thermodynamically stable carbonate products. This work shows how Co substitution in a model mafic mineral slows carbonation rates and identifies the predominant reaction product. Understanding how Co affects metal silicate carbonation as well as its final fate is beneficial to developing new methods to recover Co from mafic and ultramafic ores. 

Summary

High-grade ores of Co are becoming scarce. There is an urgent need to find alternate Co sources to meet the increasing demand for this critical element. Mafic and ultramafic silicate minerals are abundant, yet low-grade Co ores with the potential for durable CO₂ storage. Researchers used in-situ high-pressure infrared spectroscopy to show that Co substitution for Mg in forsterite slows carbonation rates under low-water, humidified CO₂ conditions compared to the pure, Co-free mineral. The Co-substituted system gives Co-doped magnesite as the predominant carbonate product. The lower carbonation rates are likely due to thermodynamic drivers that cause the water films on Co-doped forsterite to be much less oversaturated with ions that precipitate as Co-doped magnesite than in the undoped system. This fundamental knowledge will help researchers develop methods that lower the cost of Co extraction from mafic or ultramafic rocks, help the mining industry reach net-zero CO₂ emissions, and decrease water usage and waste.

Contact

John Loring, Pacific Northwest National Laboratory, john.loring@pnnl.gov 

Sebastien Kerisit, Pacific Northwest National Laboratory, sebastien.kerisit@pnnl.gov 

Funding

This work was supported by the Department of Energy (DOE), Office of Science, Basic Energy Sciences program, Chemical and Materials Sciences to Advance Clean Energy Technologies and Low-Carbon Manufacturing (FWP 80281). Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by the Battelle Memorial Institute under Contract DE-AC05-76RL01830. Part of this research was performed at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility at PNNL sponsored by DOE’s Biological and Environmental Research program and located at PNNL in Richland, WA.