Surface charge and metal ion adsorption on an H-type activated carbon: experimental observation and modeling simulation by the surface complex formation approach

Experimental and modeling studies on both surface charge and adsorption of metals on an H-type activated carbon were conducted. The surface charge density decreased with an increase in pH and a decrease in ionic strength. Higher copper adsorption percentage was achieved with higher pH and ionic strength and lower initial concentration. The metal uptake was in the descending order of Cu2+ > Zn2+ approximate to Co2+. Zinc and cobalt did not affect the copper removal; however, adsorption of both reduced in the presence of copper. The two-pK triple layer surface complex formation model successfully elucidated the surface charge density and metal adsorption in various conditions (pH, ionic strength, anions, single- and multiple-metal ions, and initial concentration). Modeling revealed that the copper removal was due to adsorption of Cu2+, CuOH+ and CuCl+ on the activated carbon. Zinc and cobalt uptake resulted from the formation of the surface-metal complexes (SO-M2+ and SO-MOH+, M=Zn, Co). Based on the parameters from the modeling of surface charge density and single-metal-ion removal (i.e. Cu, Zn and Co), modeling multiple-metal-ion adsorption (Cu-Zn, Cu-Co and Cu-Zn-Co) was performed. It was demonstrated that the model described well the competitive effects on the metal adsorption. Finally, sensitivity analysis of model parameters was conducted. (C) 2001 Elsevier Science Ltd. All rights reserved.