Factors Affecting the Adsorption of Complexed Heavy Metals on Hydrous Al₂O₃

Factors influencing the adsorption behavior of heavy metals, viz Cu(II), Zn(II), Cd(II), Pb(II) and Ni(II), onto Al₂O₃ from aqueous solutions containing complexing ligands were investigated using batch adsoption experiments. For the Cu(II)/NTA/ γ-Al₂O₃, system, increasing the system ionic strength reduced Cu adsorption through activity coefficient and surface electrical double layer effects. The presence of alkaline earth cations (Ca(II) and Mg(II)) also reduced Cu removal from solution by lowering the ability of NTA to prevent Cu(OH)₂ precipitation and through specific adsorption to the alumina surface. The adsorption of the heavy metals on Al₂O₃ from solutions containing NTA followed the sequence: Cu >Zn > Cd > Pb ≈ Ni. Increase in system temperature tended to decrease metal adsorption.