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 den sity decreased with an increase in pH and a decrease in ionic strength. Hig her copper adsorption percentage was achieved with higher pH and ionic stre ngth and lower initial concentration. The metal uptake was in the descendin g 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 successfull y elucidated the surface charge density and metal adsorption in various con ditions (pH, ionic strength, anions, single- and multiple-metal ions, and i nitial concentration). Modeling revealed that the copper removal was due to adsorption of Cu2+, CuOH+ and CuCl+ on the activated carbon. Zinc and coba lt 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 surf ace charge density and single-metal-ion removal (i.e. Cu, Zn and Co), model ing 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.