Raw and modified palygorskite in water treatment applications for low-concentration ammonium removal

Raw palygorskite (Pal) samples went under acid (H-Pal), NaCl (Na-Pal), and CaCl₂ treatment (Ca-Pal) in order to be examined as ammonium (NH₄ ⁺ ) sorbents from aqueous solutions. The samples were characterized by XRD and FT-IR techniques to examine potential structural differences after modifications, and batch kinetic experiment series were applied to determine the optimal conditions for NH₄ ⁺ removal. According to thermodynamic analysis, the removal reaction for sodium- and calcium-treated samples was endothermic (ΔΗ⁰  > 0, 1.65 kJ/mol and 24.66 kJ/mol, respectively), in contrast with the exothermic reactions of raw and acidic-treated palygorskite samples (ΔΗ⁰  < 0, -37.18 kJ/mol and -27.56 kJ/mol respectively). Moreover, each sample presented a different order of sorbed ions preference, whereas the strong affinity for Ca²⁺ sorption was common in all cases since the NH₄ ⁺ removal inhibited. Nevertheless, a similar pattern was followed for raw and modified samples at isotherm study, rendering the linear form of Freundlich isotherm to express better the NH₄ ⁺ sorption on palygorskite sample, indicating that it is a heterogeneous procedure. In all cases, the NH₄ ⁺ maximum uptake was within 15 min using 8 g/L of each sorbent, especially for the Na-Pal sample, which could reach almost 100% removal of low concentration NH₄ ⁺ . PRACTITIONER POINTS: Modified palygorskite samples were tested for NH₄ ⁺ removal from aqueous solutions. NaCl-treated palygorskite had the higher removal efficiency, which could reach almost 100% removal of low concentration NH₄ ⁺ . NH₄ ⁺ maximum uptake was within 15 minutes using 8 g/L of each sorbent. NH₄ ⁺ adsorption was an endothermic reaction for NaCl- and CaCl₂ -treated palygorskite sorbents. NH₄ ⁺ adsorption was an exothermic reaction for raw and acid-treated palygorskite sorbents.