Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite

► PANI was successfully incorporated onto the surface of ATP clay. ► ATP–PANI showed high adsorption capacity for HA dependent on pH and ionic strength. ► The adsorbent can be regenerated in alkaline solution and used repeatedly. ► Electrostatic interaction played an important role in the enhanced HA adsorption. Polyaniline/attapulgite composite (ATP–PANI) was prepared by in situ chemical oxidation and characterized by FITR, XRD, and TEM. Characterized results showed that polyaniline (PANI) was successfully encapsulated on the surface of attapulgite (ATP). Humic acid (HA) adsorption onto ATP–PANI was investigated by batch experiments and adsorption kinetic tests. In contrast with the low HA adsorption amount on ATP, substantially enhanced HA adsorption onto ATP–PANI was observed. Adsorption isotherms of HA can be well described by Langmuir model and the maximum adsorption amounts were found to be 43.01, 52.91, 61.35 mg/g at 15, 25, and 35 °C, respectively. HA adsorption increased with rise in temperature indicating of an endothermic process of HA adsorption onto ATP–PANI. Pseudo-second order kinetic equation can fit HA adsorption very well and the adsorption rate decreased with increasing initial HA concentration. HA adsorption decreased monotonously with increasing solution pH. Co-existed cations (Na +, K +, Ca 2+) in aqueous solution improved HA adsorption amount on ATP–PANI, and the augment of HA adsorption amount was order as Ca 2+ > K + > Na +. Results of HA adsorption onto ATP–PANI showed that the electrostatic interaction between amine and imine groups of the adsorbents and HA molecules in solution may account for the enhanced HA adsorption. The HA molecules adsorbed on ATP–PANI can be effectively desorbed in 2 M NaOH solution, and regenerated adsorbent can be repeatedly used in the subsequently four adsorption-regeneration cycles with little loss of HA adsorption amount.