Adsorption of Cu(II), Pb(II) and humic acid on natural zeolite tuff in single and binary systems

A natural zeolite tuff was used for adsorption of heavy metals, Cu2+ and Pb2+, and humic acid (HA) in aqueous solution. Its adsorptive behaviour was investigated in both single component and binary component systems. For single component system, the adsorption capacities of Cu2+, Pb2+ and humic acid at 30 °C, pH 5 are 23, 68 and 78 mg/g, respectively. Solution pH was found to influence the adsorption. For heavy metals, adsorption is enhanced at higher pH while humic acid adsorption is reduced when solution pH is increased. In Pb2+/humic-acid system, Pb2+ exhibits competitive adsorption with humic acid on the natural zeolite, resulting in reduced adsorption of both Pb2+ and humic acid. However, in Cu2+/humic-acid system, competitive adsorption and complexation between Cu2+ and humic acid influence the adsorption, resulting in decreased adsorption of humic acid but increased adsorption of Cu2+. The complexation structure of Pb–HA/zeolite and Cu–HA/zeolite in three-component system was proposed as S-Pb–HA and S-HA-Cu, respectively.