Surfactant modified zeolite as adsorbent for removal of humic acid from water

Coal fly ash is a solid waste generated in large amounts worldwide; therefore, development of new techniques for its productive reuse is important. Two zeolites synthesized from coal fly ashes (ZFAs) were prepared and then modified using hexadecyltrimethylammonium (HDTMA). Both ZFAs and surfactant modified ZFAs (SMZFAs) were investigated for their ability to adsorb humic acid (HA) from water. The results indicated that, while ZFA had little affinity for HA, SMZFA showed greatly enhanced adsorption capacity. The adsorption isotherm was well fitted to the Langmuir model. The uptake of HA was substantially influenced by pH, increasing under acidic pH conditions. The SMZFA, which had a higher BET area and higher amount of loaded HDTMA, showed greater retention of HA. Uptake of HA by SMZFA was improved in the presence of NaCl. The retention of HA by SMZFA was primarily attributed to HDTMA loaded onto the zeolite surface. However, because modification of ZFA by HDTMA resulted in an increase in Zeta potential, iron oxide in SMZFA also contributed to HA adsorption via a ligand exchange mechanism.