Ab Initio Molecular Dynamics Study of a Highly Concentrated LiCl Aqueous Solution

Abstract

The properties of a highly concentrated aqueous lithium chloride solution (|LiCl| = 14 mol L(-1)) are investigated using Car-Parrinello molecular dynamics. The coordination spheres of lithium ions, chloride ions, and water molecules are described successively. On the whole, our simulation provides results-distances and coordination numbers-in very good agreement with experimental data. The lithium solvation shell is found to exhibit a tetrahedral configuration on average, with three stable clusters observed during the simulation: Li(+)-4H2O, Li(+)(H2O)3Cl(-), and Li(+)(H2O)2(Cl(-))2. The chloride coordination sphere is logically formed by strong Cl-H hydrogen bonds with neighboring water molecules, for a mean coordination number of 4.4. The structuring of water molecules is strongly affected by the high concentration in LiCl. The hydrogen bond network is globally broken down, but little variation is calculated on water dipoles (μ = 3.07 D) because of the strong polarization from Li(+) and Cl(-) ions. We also point out some of the characteristic features of such a highly concentrated solution: water bridging between Li(+) and Cl(-) hydration spheres, Li(+)-Cl(-) ion-pairing, and intermediate behavior between dilute solutions and molten salts. Finally, the reliability of our simulation to describe ion-pairing is discussed.

Hydrothermal transport, deposition, and fractionation of the REE: Experimental data and thermodynamic calculations

“…For example, the molecular dynamic study of Terrier et al (2010) showed that in the case of La 3+ , polarization of the water molecules located in the first shell gives rise to dipole moments about 0.5 debye larger than those of bulk water molecules (3.0 debye in pure water at room temperature). Petit et al (2008) noticed the same effect for water molecules in the LaCl 2 (H 2 O) 6 + complex, and also showed that the dipole moment of chloride ions increases from 0.52 debye in the solution to 1.39 debye within the complex. Given the strong correlation between dielectric properties and hydration energy, and the strong change in dielectric properties of solutions with temperature and pressure (Sherman, 2010), this effect is expected to play a key role in controlling REE 3+ speciation in hydrothermal fluids.…”

“…Given the strong correlation between dielectric properties and hydration energy, and the strong change in dielectric properties of solutions with temperature and pressure (Sherman, 2010), this effect is expected to play a key role in controlling REE 3+ speciation in hydrothermal fluids. (ii) Petit et al (2008) used first principle molecular dynamic simulations to investigate the speciation of La 3+ in a~13 molal chloride solution (35 wt.% LiCl equivalent) at ambient temperature. They found that the most stable configuration consists of two Cl − and six water molecules arranged in a square antiprism geometry (Fig.…”

“…Coordination and hydration of REE 3+ aqua ions (c,d) and LaCl 2 + (a,b) at room temperature according to experimental and first-principle molecular dynamic data(Persson, 2010;Petit et al, 2008).…”

Dynamics of water clusters in solution with LiCl

“…Furthermore, Molecular Dynamics (MD) simulations showed that the water tendency to develop its characteristic tetrahedral network provokes a segregation of the system. The ions are not included in the network of water molecules and contribute to the formation of solute rich regions within the system [32,33].…”

Aqueous solutions: state of the art in ab initio molecular dynamics

“…In this regard, the AIMD studies have also shown that the first hydration shells of both Ca 2+ and Mg 2+ are structurally anisotropic. Mixed systems consisting of ion pairs with varying concentrations have also been studied [128,130,131,133,135,136]. In the case of NaOH and KOH [137], a clear influence of the counterion on the hydration structure of the hydroxide ion has been demonstrated.…”