Molecular-scale adsorption mechanisms and mechanical stability of sepiolite for Li+, Na+ and K+ storage: Insights from molecular dynamics simulations

Sepiolite, a hydrated magnesium silicate known for its fibrous structure, is extensively utilized in water treatment for its ability to adsorb a variety of metal ions. Despite its widespread utilization, the mechanical properties of sepiolite, which are crucial for its practical applications, have been largely overlooked. To address this gap, this paper employs molecular dynamics (MD) simulation to explore the mechanical characteristics of sepiolite, including structural parameters, bulk modulus, and Young's modulus. The research findings reveal that zeolitic water molecules contribute positively to enhancing the mechanical properties of sepiolite. As the number of zeolitic water molecules rises, the Young's modulus values in the x and y directions show a clear increasing trend. However, the quantity of zeolitic water molecules does not significantly affect the Young's modulus in the z direction or the Poisson's ratio. Additionally, the paper assesses the adsorption capacity of sepiolite for Li⁺, Na⁺, and K⁺. The results indicate that as ion concentration rises, the absolute number of ions adsorbed onto the surface increases, yet the corresponding adsorption percentage shows a notable decline. Based on the adsorption capacity, the ion selectivity order of sepiolite is determined to be: Na⁺ > Li⁺ > K⁺. The MD simulations elucidate the adsorption mechanism by which alkali metal ions interact with and adhere to the sepiolite surface.