Hydration,dissolution and nucleation processes at the alpha-quartz (0001) surface in liquid water

Scientific problem

Many geochemical processes involve the formation and dissolution of the solid phase,which largely depends on the molecular interaction of surface species with those in the aqueous matrix. Thus, the interaction of water with the quartz surface has also been the subject of a variety of experimental and computational studies.However, computer simulation studies of the solid/water interface are generally carried out in vacuo with the water adsorbed from the gas phase onto the surface, or at clusters representing the surface,even though the experimental water layer adsorbed at the quartz/water/air interface is often many nanometers thick. So far, most if not all computational studies of the silicate/water interface have concentrated on adsorption of single water molecules or monolayers. In our MD simulations, we have included both temperature and a realistic liquid water environment for the investigation of multi-layer hydration, dissolution and nucleation processes at the two different quartz (0001) surface terminations.

Scientific results

Our study indicates that the structure of the water layers near the surfaces is affected by the nature of the substrate surface and by temperature.

Our results also suggest that on thermodynamic grounds the complete dissolution of silicon atoms from the quartz surfaces in a liquid water environment is unlikely to occur, but that the formation of a Si(OH)₃ species at the surface would be possible.

This work has shown that entropy needs to be taken into account when nucleation/dissolution processes are calculated from computer simulations.

This study not only involved a large amount of calculations in terms of length and time-scales but also involved very large data sets. The use of newly developed eMinerals minigrid and SRB makes the scientific research more efficient.

Snapshots of the structure of interfacial water molecules near the Si-O-Si bridged surface at 300K, during equilibration (left); during production (right).

Credits

This work was carried out by Zhimei Du and Nora de Leeuw (Birkbeck).