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 CaCl treatment (Ca-Pal) in order to be examined as ammonium (NH ) 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 NH removal. According to thermodynamic analysis, the removal reaction for sodium- and calcium-treated samples was endothermic (ΔΗ  > 0, 1.65 kJ/mol and 24.66 kJ/mol, respectively), in contrast with the exothermic reactions of raw and acidic-treated palygorskite samples (ΔΗ  < 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 Ca sorption was common in all cases since the NH 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 NH sorption on palygorskite sample, indicating that it is a heterogeneous procedure. In all cases, the NH 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 NH . PRACTITIONER POINTS: Modified palygorskite samples were tested for NH removal from aqueous solutions. NaCl-treated palygorskite had the higher removal efficiency, which could reach almost 100% removal of low concentration NH . NH maximum uptake was within 15 minutes using 8 g/L of each sorbent. NH adsorption was an endothermic reaction for NaCl- and CaCl -treated palygorskite sorbents. NH adsorption was an exothermic reaction for raw and acid-treated palygorskite sorbents.