Brazilian clays as natural cation exchangers for copper sorption in a batch system

This study evaluated Brazilian natural clays for copper sorption from water. Clays were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and sorption tests. Affinity tests showed that brasgel (B, 69%), chocobofe (Cb, 46%), and chocolate (Ch, 41%) had higher Cu²⁺ capture potential than zeolite (Z, 26%), palygorskite (P, 18%), treated palygorskite (TP, 11%), and cloisite 20A (C20A, 4%). The capture of Cu²⁺ by clays and zeolite occurs with the release of light metal ions, especially Na⁺, Mg²⁺ and Ca²⁺, which were initially present in the nanomaterials structure. The organomodification of clays possibly altered specific surface area, affecting Cu²⁺ removal. Besides, the lamellae morphology of B, Cb, and Ch and their crystalline structure of smectites facilitated the metal ion removal. Next, B, Cb, and Ch clays were selected based on their affinity with Cu²⁺ to investigate these systems’ sorption kinetics and equilibrium isothermal. The sorption kinetics showed that the equilibration time was reached within 120 min for all clays. The Pseudo-second order (PSOR) and External mass transfer resistance (EMTR) models effectively represented the kinetics data. The isothermal equilibrium revealed that the maximum uptake capacity for clays by Cu²⁺ increased in the following order: B (0.264 mmol g⁻¹) > Cb (0.223 mmol g⁻¹) > Ch (0.177 mmol g⁻¹). The isothermal curves better fit the Freundlich (B nanoclay) and Langmuir (Cb and Ch clays) models. The findings suggest that Brazilian clay nanostructures, particularly B, Cb, and Ch, are promising nanoadsorbents for removing bivalent copper ions from aqueous solutions.