Molecular Insights of Separation of Lanthanide Metals from Aqueous Waste by Using Directional Solvent Extraction

In this paper, we present atomistic molecular dynamics simulations to understand the directional solvent extraction (DSE) for separating lanthanide metals from aqueous waste. We consider four different lanthanide metals such as lanthanum (La³⁺), neodymium (Nd³⁺), europium (Eu³⁺), and ytterbium (Yb³⁺) using decanoic acid (DEC) as a directional solvent. We analyze various molecular mass density profiles, intermolecular structural properties, ion dynamic behaviors, and solvation free energy values of metal ions with the variation in temperature (T). We observe strong intermolecular interactions between the lanthanide ions (Ln³⁺–Ln³⁺) and lanthanide–nitrate (Ln³⁺–NO₃) as the temperature increases. The self-diffusion coefficient (D) of all of the metal ions shows a significant rise with an increase in T values. The detailed solvation free energy ΔG_solv (kJ/mol) and transfer free energy ΔG_transfer (kJ/mol) calculations provide favorable values in the organic and aqueous phases with the rise in T values. The partition coefficient (log P) values indicates favorable separation of lanthanide ions using DEC. Overall, the molecular level findings described in this manuscript provide great insights into the design of the DSE method for the separation of lanthanide metals from aqueous waste.