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 Cu(2+) adsorption on the activated. (C) 2007 Elsevier B.V. All rights reserved.