Enhanced Removal of Humic Acid from Aqueous Solution by Adsorption on Surfactant-Modified Palygorskite

Surfactant-modified palygorskite (PA) samples were prepared and used as adsorbents to remove aqueous humic acid (HA). Characterization results confirmed the successful modification of PA by the surfactants. Surfactant modification of PA remarkably improved its adsorption for aqueous HA, and the HA adsorption increased with increasing alkyl chain length of the surfactants, indicating that hydrophobic interaction and electrostatic interaction are the driving forces for HA adsorption. The adsorption amount of HA onto the surfactant-modified PA was well described by the Freundlich model, and the maximum adsorption amount of HA on PA-OTAC, PA-DTAC, and PA-CTAC was 57.43, 199.86, and 253.00 mg/g over the tested concentration range. The pseudo-second-order kinetic model fitted the HA adsorption on PA-CTAC very well. HA adsorption on PA-CTAC decreased with increasing solution pH, and the presence of cations in water increased HA adsorption on the adsorbent. The PA-CTAC loaded adsorbent was easily desorbed in 0.1 mol/L NaOH, and the regenerated adsorbent showed have good adsorption capability for HA.