Single and co-adsorption of heavy metals and humic acid on fly ash

Heavy metals and humic acid are two important pollutants in surface and waste water systems. In this study, fly ash, an industrial waste, is used as a low-cost adsorbent for simultaneous removal of heavy metals and humic acid. The investigations were conducted for individual pollutant adsorption along with co-adsorption of both pollutants. It is found that, for single pollutant system, fly ash can achieve adsorption of lead ion at 18 mg/g, copper ion at 7 mg/g and humic acid at 36 mg/g, respectively. For co-adsorption, complexation of heavy metals and humic acid plays an important role. The presence of humic acid in water will provide additional binding sites for heavy metals, thus promoting metal adsorption on fly ash. For Pb–HA and Cu–HA systems, Pb2+ and Cu2+ adsorption can increase to 37 and 28 mg/g, respectively, at pH 5 and 30 °C. However, the heavy metal ions present in the system will compete with the adsorption of humic acid on fly ash, thus resulting in a decrease in humic acid adsorption. For all cases, dynamic adsorption can be described by the first-order and second-order kinetics.