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 minutes using 8 g/L of each sorbent, especially for the Na-Pal sample, which could reach almost 100 % removal of low concentration NH4+ .