Crystallization of Carbonates with a Core-Shell Structure: Insights into Cobalt-Iron Separation for Enhanced Critical...

Area of Science:

• Geochemistry
• Mineralogy
• Environmental Science

Background:

• Carbonation of mafic and ultramafic silicates is a key strategy for carbon removal.
• Cobalt, iron, and calcium often coexist with magnesium in these minerals, influencing carbon mineralization and critical element recovery.

Purpose of the Study:

• To investigate the coprecipitation dynamics of magnesium carbonate with minor cations (cobalt, iron, calcium) under simulated geological conditions.
• To understand how these multi-ion systems affect carbon mineralization kinetics and mineral structure for optimized carbon capture and element recovery.

Main Methods:

• Coprecipitation experiments were performed at 95 °C and 30 bar CO2 with varying concentrations of Mg, Co, Fe, and Ca.
• Solid products were characterized to determine mineral structure and cation distribution.
• Triple-cation (Co-Fe-Mg) experiments under aerobic conditions were conducted to assess phase separation.

Main Results:

• Carbonate particles formed with a core-shell structure, encapsulating minor cations within a magnesite shell.
• The presence of minor cations, particularly cobalt, accelerated magnesite (MgCO3) crystallization.
• Magnesium slowed the precipitation of minor cation carbonates, and under aerobic conditions, MgCO3 formation led to the isolation of cobalt and iron.

Conclusions:

• Minor cations significantly alter carbonation kinetics and mineral heterogeneity in multi-ion systems.
• The findings provide a scientific basis for optimizing cobalt and iron separation during carbon mineralization processes for enhanced critical element recovery.