Molecular dynamics simulations of Li+/Mg2+ separation using metal-organic frameworks

In this work, we investigate the extraction of Li+ from solutions containing Li+ and Mg2+ using metal-organic framework (MOF) membranes through molecular dynamics simulations (MD). Five MOFs with different pore sizes are studied. It is found that there is a critical pressure for MOFs with pore size smaller than 7.08 Å, below which Li+ can be completely separated from Mg2+. This critical pressure increases as the pore size decreases. Under practical pressures (< 50 MPa), MOFs with pore size around 6.5-7.0 Å are optimal for complete separation of Li+ and Mg2+. If high pressures can be reached, MOF with pore size of 5.48 Å appears to perform better because it ensures not only perfect separation but also a high flux of Li+. The hydration energy, potential of mean force, and density distribution of Li+ and Mg2+ are computed to explain the separation mechanisms.