Solvation of the vanadate ion in seawater conditions from molecular dynamics simulations

[Display omitted] •Molecular dynamics simulations show that vanadium(V) exists as NaHVO4− in seawater.•Na+ ion in NaHVO4− has two interchangeable states: bidentate and monodentate.•The Na+ ion interacts with two vanadate oxo groups in the bidentate state.•The Na+ ion interacts with only one vanadate oxo group in the monodentate state.•A small barrier separates the two states of Na+ ion in NaHVO4−. One of the current challenges present in uranium extraction from seawater is the competitive sorption of vanadium. But compared with uranium, much less is known about the solvation and speciation of the vanadate ion in seawater. Herein, we utilize both first principles molecular dynamics and classical molecular dynamics simulations to provide a microscopic insight into the solvation of the HVO42− ion in pure water and in seawater. In pure water, we found that the dianion state is the most probable structure. But in a simulated seawater with 0.55M NaCl, the NaHVO4− ion is most probable, followed by the neutral Na2HVO4; averaging over 100-ns trajectory, the coordination number of Na+ ions around V was found to be 1.5 within a radius of 4.0Å. We found that the NaHVO4− ion can exist in two interchangeable states: a bidentate state where the Na+ ion interacts directly with two vanadate oxo groups; a monodentate where the Na+ ion interacts with only one vanadate oxo group. From this monodentate state, the Na+ ion can further dissociate away with a free-energy barrier of 2.5kcal/mol. Our work therefore demonstrates that Na+ ions are closely associated with the vanadate species in seawater.