Resemblance between the naturally occurring and the computed crystal structure morphology (left). The 2D free energy surface as a function of the distance (z) from the central layer and the number of water-water hydrogen bonds (n), highlighting the multilayered water structure and the associated exchange timescales at the water-xenotime interface(right).

Simulations reveal precisely how water and ligands bind to the surface of a rare earth mineral

Resemblance between the naturally occurring and the computed crystal structure morphology (left). The 2D free energy surface as a function of the distance (z) from the central layer and the number of water-water hydrogen bonds (n), highlighting the multilayered water structure and the associated exchange timescales at the water-xenotime interface(right).
Resemblance between the naturally occurring and the computed crystal structure morphology (left). The 2D free energy surface as a function of the distance (z) from the central layer and the number of water-water hydrogen bonds (n), highlighting the multilayered water structure and the associated exchange  timescales at the water-xenotime interface(right).

A collaboration between ORNL and UC-Davis led to this highlight

Achievement
Ab initio molecular dynamics (AIMD) simulations resolve the hydration structure and water-exchange kinetics at the water–xenotime interface.

Significance and impact
AIMD simulations establish that {100} xenotime surface can only accommodate monodentate coordination of a bidentate hydroxamate collector. Differences in the hydration structure and water-exchange kinetics imposed by different ligands could be used to develop design strategies to enhance flotation selectivity of RE minerals.

Details and next steps

  • Different interfacial (Y3+  and PO_4^(3−)-bound) and bulk-like water layers with distinct orientations are identified on the 2D-free energy surface.
  • A Marcus rate theory reveals that water exchange occurs on 10s to 100s of ps timescales, exhibiting strong sensitivity to ligand orientation, which prompts us to develop new strategies for selective flotation of RE. 
  • Our methodology is transferable to the study of water-exchange kinetics and ligand adsorption on bastnaesite.