Competition and complexation of heavy metal ions and humic acid on zeolitic MCM-22 and activated carbon

Zeolitic MCM-22 and activated carbon have been used as adsorbents for removal of heavy metals (Cu^2+ and Pb^2+) and humic acid from aqueous solution. The adsorption behaviour has been investigated in single- and binary-adsorbate systems and the effect of humic acid on metal adsorption was obtained. It is found that the MCM-22 and activated carbon are effective in metal ion and humic acid adsorption. In single component system, the MCM-22 presents the adsorption capacities of Cu^2+, Pb^2+, and humic acid at 33, 94, and 78 mg/g, respectively, while the activated carbon exhibits the adsorption capacities of Cu^2+, Pb^2+, and humic acid at 12, 61, and 74 mg/g, respectively, lower than those on the MCM-22. Solution pH will significantly influence the adsorption. Cu^2+ and Pb^2+ adsorption will increase with increasing pH while humic acid shows a decreasing trend as pH is increased. In binary-adsorbate system, metal–humic acid interaction will affect the adsorption of metal and humic acid on the MCM-22 and activated carbon. On the MCM-22, Cu^2+, Pb^2+ will present competitive adsorption with humic acid. On the activated carbon, Pb^2+ and humic acid also exhibit competitive adsorption, while Cu^2+ and humic acid will have a complexation effect, resulting in an increase of Cu2+ adsorption on the activated.