149-3 Selective Li+/Mg2+ adsorption on montmorillonite and layer double hydroxides for Li recovery

Session: Research to Accelerate Recovery of Critical Minerals from Primary and Secondary Resources (Posters)

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Abstract:

Separation of Li⁺ from Li⁺/Mg²⁺ mixtures is widely used as a model system for investigating lithium recovery from brine. In this study, we explore the use of two oppositely charged minerals—negatively charged montmorillonite (MMT) and positively charged layered double hydroxide (LDH)—to selectively adsorb Li⁺ over Mg²⁺. Molecular dynamics simulations reveal that adsorption occurs through electrostatic interactions within the electric double layer: Li⁺ and Mg²⁺ are directly attracted to MMT surfaces, whereas in LDH, interactions are mediated by Cl⁻ ions. Ion pairing between the cations and Cl⁻ plays a critical role in the LDH system. Potential of mean force calculations reveal that, at 1 M concentration, the free energy change is favorable for Li⁺ to form both contact ion pairs (-0.41 kcal/mol) and solvent-separated ion pairs (SSIP, -0.52 kcal/mol) with interfacial Cl^-, whereas Mg²⁺ forms only SSIP (-0.67 kcal/mol) due to its highly stable solvation shell. This dual mode of Li⁺–anion interaction suggests enhanced adsorption selectivity at the LDH. In experimental analysis, we embedded these adsorbents in a polyether sulfone polymer matrix.  Preliminary experimental results demonstrate enhanced Li⁺ selectivity (, unitless) of MMT and LDH in the presence of a 2000 ppm feed solution with a 20:1 weight ratio of Mg²⁺:Li⁺, significantly reducing the amount of difficult to separate Mg²⁺ in the resultant post adsorption solution. Additionally, the adsorbents demonstrate promising Li⁺ adsorption values ( mg g^-1), of MMT and LDH , on par with or exceeding commercial Li⁺ adsorbents capacity which offer  values of 5-6.  These results reveal these adsorbents as a promising approach for lithium recovery using natural materials.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9395

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