Microscopic evidence for liquid-liquid separation in supersaturated CaCO3 solutions

Area of Science:

• Geochemistry
• Materials Science
• Chemical Physics

Background:

• Classical nucleation theory predicts unstable clusters during CaCO3 mineralization.
• Experimental observations suggest stable CaCO3 clusters emerge instead.
• Discrepancies necessitate new models for early-stage mineralization.

Purpose of the Study:

• Investigate the structure, dynamics, and energetics of hydrated CaCO3 clusters.
• Explore cluster population behavior before nucleation using lattice gas simulations.
• Reconcile experimental observations with theoretical predictions of CaCO3 formation.

Main Methods:

• Molecular dynamics simulations of hydrated CaCO3 clusters.
• Lattice gas simulations for pre-nucleation cluster dynamics.
• Analysis of cluster structure, dynamics, and energetics.

Main Results:

• Predicted formation of a dense liquid phase via liquid-liquid separation.
• Observed stable, hydrated CaCO3 clusters within a specific concentration range.
• Coalescence and solidification of nanoscale droplets leading to amorphous CaCO3.
• Identification of a liquid-liquid binodal supporting phase-separation mechanisms.

Conclusions:

• The study supports a phase-separation mechanism for CaCO3 mineralization.
• Stable liquid-like CaCO3 clusters precede amorphous solid formation.
• Findings reconcile experimental data with established physical chemistry principles.