The removal of thallium (Tl⁺), a highly toxic heavy metal, from aqueous environments is a critical environmental challenge. Zeolites, crystalline microporous aluminosilicates with tunable composition and high cation-exchange capacity, are widely used in environmental remediation due to their ability to selectively capture metal ions from contaminated waters.

We investigated the selective uptake of Tl⁺ by potassium-form L zeolite (K-L) and evaluated the structural adaptations accompanying cation exchange using X-ray powder diffraction (XRPD), Rietveld refinements, thermal analysis, and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Two additional zeolitic materials—protonated ferrierite (obtained by calcination of its ammonium form) and 13X zeolite, commonly used in environmental applications—were also tested. Batch adsorption experiments were conducted at neutral pH (~7), including isotherms and kinetic studies for 13X. All three materials were further assessed in real Tl-contaminated waters (~17 ppb).

All zeolites achieved nearly 100% Tl⁺ removal in synthetic solutions at 500 ppm and retained significant uptake at high concentrations (~0.5 M). Structural refinements revealed concentration-dependent framework responses: K-L showed minimal lattice expansion at low Tl⁺ loading and anisotropic expansion at high loading, associated with K⁺/Tl⁺ exchange, reduced hydration, and extraframework reorganization. Similar trends were observed for ferrierite and 13X. In real waters, despite competing ions, all three zeolites reduced Tl⁺ concentrations to ~2 ppb.

Tl⁺ incorporation induces precise structural adaptations in zeolitic frameworks, including selective cation redistribution, anisotropic channel expansion, and reorganization of the water network. K-L, 13X, and protonated ferrierite demonstrate high efficiency for Tl⁺ removal from both synthetic and natural waters, highlighting their strong potential for environmental remediation of thallium-contaminated systems.