Atomic insights into flotation separation of KCl and NaCl from a new viewpoint of hydration layer: A molecular dynamic study

The flotation separation of sylvite (KCl) and halite (NaCl) had drawn much attention, but the mechanism is still controversial. In this work, the atomic insights into the flotation separation of KCl and NaCl was conducted using molecular dynamics simulation (MDs). A novel concept that the hydration layer on minerals surface has been introduced. The molecular dynamic calculation shows that the adsorption energy between the octadecylamine (ODA, the most common collector for KCl flotation) and NaCl is smaller than the cohesive energy in the hydration layers on NaCl surface. However, the adsorption energy of ODA/KCl is much larger than the cohesive energy of the hydration layers on KCl surface. Hence, the collector ODA can pass through the hydration layers and then be adsorbed onto the KCl surface, but that cannot do occur on the NaCl surface, which perfectly explains the mechanism of the separation of KCl and NaCl by ODA. Notably, the new viewpoint of hydration layer may open up a new path to explain the behavior of flotation separation. The flotation experiment results also show the KCl is easily floated while the NaCl hardly floated by ODA, which agrees well with the calculation results.