Ionic dissolution and precipitation of KBF4 and NaBF4 aqueous solutions

Abstract

The investigation on tetrafluoroborate aqueous solutions is of great significance for the utilization of rare earth resources. We have performed a series of molecular dynamics simulations of KBF4 and NaBF4 aqueous solutions at concentrations ranging from 0.5 M to 2.5 M to investigate the solvation kinetics of ions. It has been found that the difference in solubility between KBF4 and NaBF4 depends on the direct interaction of ions with water molecules in the first hydrated shell. On average, water molecules spend more time in the immediate vicinity of Na+ ions than in the immediate vicinity of K+ ions and BF4− ions have more likely to form a contact ion pair with K+ ions. The static dielectric constant of KBF4 and NaBF4 aqueous solutions decreases and the dielectric relaxation time increases. The tetrahedral structure of water was found to exhibit varying degrees of distortion with the ion concentration of the solution studied herein. These findings highlight the importance of the first hydrated shell under solubility mechanism for KBF4 and NaBF4.