Substrate Structure Influences Critical Mineral Availability in Shallow Subsurface Environments
The Science
Cobalt (Co) is a critical mineral found in existing and emerging technologies, making understanding its behavior in natural systems essential for developing a robust and secure supply chain. Researchers studied the formation of Co minerals on two different carbonate surfaces at a range of temperatures and Co concentrations. By taking a systematic approach to isolating the thermodynamic and kinetic factors that control Co speciation, the team produced a clearer understanding of how the temperature and mineral surface dictate which Co-bearing solid forms. They found that competition between Co carbonate and hydroxide phases is strongly dependent on both temperature and the type of mineral substrate present.
The Impact
To effectively manage Co resources, it is necessary to understand what controls the fate of dissolved Co when it interacts with the carbonate minerals common in geological systems. Knowledge of this “phase selection” is critical for predicting Co’s mobility in nature and for designing better methods to recover this valuable resource.
Summary
Co, noted as a critical mineral for energy by the Department of Energy, can be trapped by interacting with existing mineral surfaces in natural systems. Understanding the underlying mechanisms of how Co immobilizes on commonly occurring carbonate surfaces under different conditions is essential for predicting its mobility, availability, and recovery. Researchers investigated the temperature-dependent competition between CoCO3 and Co(OH)2 formation on calcite (CaCO3) and magnesite (MgCO3) surfaces. Using X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, they analyzed carbonate substrates exposed to Co chloride solutions at varying concentrations (0–500 μM) and temperatures (22°C, 50°C, and 80°C). Magnesite surfaces generally promoted CoCO3 formation because of the low lattice mismatch between the two materials. However, Co(OH)2 formation on MgCO3 outcompeted the slow-growing CoCO3 as the temperature and/or initial Co concentration increased. On calcite surfaces, the poor lattice mismatch between CaCO3 and CoCO3 led to Co(OH)2 outcompeting CoCO3 formation across all three temperatures and Co concentrations. These findings provide insights into the roles of substrate composition, solution chemistry, and temperature in controlling Co speciation and mobility, with important implications for geochemical cycling and the industrial recovery of Co in carbonate-rich systems.
Contact
Sebastien Kerisit, Pacific Northwest National Laboratory, sebastien.kerisit@pnnl.gov
Sebastian Mergelsberg, Pacific Northwest National Laboratory, sebastian.mergelsberg@pnnl.gov
Kevin Rosso, Pacific Northwest National Laboratory, kevin.rosso@pnnl.gov
Funding
This research was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division through its Geosciences Program (FWP 56674) at Pacific Northwest National Laboratory (PNNL). PNNL is operated for DOE by Battelle Memorial Institute under Contract No. DE-AC06-76RLO-1830. Part of the research was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the U.S. DOE’s Biological and Environmental Research program.
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