Low temperature molecular dynamic simulation of water structure at sylvite crystal surface in saturated solution

• MDS was used to study interfacial water structure at KCl crystal surfaces.
• MDS of brine and brine/KCl crystals was used to determine effect of temperature.
• At low temperature MDS, water molecules increased order at a KCl crystal surface.
• Low temperature might change KCl from water ‘structure breaker’ to ‘structure maker’.

The low flotation recovery of sylvite from salt lakes at low temperatures has dogged the cryogenic producer for many years. Interfacial water structure at sylvite crystal surfaces has been considered as one noticeable aspect on interpreting the selected KCl collection during flotation, and so the microscopic structure of the water membrane over KCl crystal surfaces at low temperatures was modeled through the use of molecular dynamics methods. In our simulation, the properties of the water membrane adjacent to KCl crystal surface, such as molecular mobility, water structure and preferred molecular orientation, were compared to the results for an otherwise identical system at higher temperatures or in saturated KCl solutions in the absence of a KCl crystal. In our simulation, hydrogen atoms approached the KCl crystal surface more closely, and the mobility of water molecules was more restricted compared to results for saturated KCl solutions. When the temperature decreased, the mobility of water molecules decreased, the number of hydrogen bonds made by the water molecules in the membranes was reduced and the molecules exhibited greater order than in other systems we studied. It was proposed that the property of KCl salt may change from water ‘structure breaker’ to ‘structure maker’ when temperature decreases. These results may provide complementary information which cannot be obtained from experiments on the research of flotation at low temperature directly.

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