Studies on the chemical behavior of metal ions in aquatic systems

Abstract

Chapter 1. Part I Hydrophobic Effects of o-Phenanthroline and 2, 2``-Bipyridine on Adsorption of Metal(II) Ions onto Silica Gel Surface The effects of o-phenanthroline and 2,2``-bipyridine on the adsorption of metal(II) (Fe, Co, Ni and Cu) ions onto silica gel surface have been studied. The adsorption is expressed in terms of the measured concentrations of both metal and ligand at equilibrium. Each adsorption of the four metal ions is increased with the presence of the ligands. In addition, adsorption increases slowly with pH at low pH values and then increases rapidly up to near $pK_a$ value of silica gel (=6.5). The adsorption of each metal ion at low pH is increased with increased ligand concentration. However, at high pH the adsorptions of Fe(II) and Cu(II) are decreased with increased ligand concentration whereas the adsorptions of Co(II) and Ni(II) are always increased. At low pH values the ligand to metal ratio adsorbed on the silica gel surface is ca. 3:1 while at high pH values it is 1:1, 2:1, and 3:1, corresponding to the initial ligand to metal ion concentration ratio. The addition of ethanol to the phenanthroline-$SiO_2$ solution results in a decrease in the adsorption of phenanthroline. The effect of ethanol is also observed in the Fe(II)-phenanthroline-$SiO_2$ system. The behavior of the adsorption is interpreted qualitatively by hydrophobic expulsion, the formation of surface complexes, and electrostatic interaction. It is concluded that hydrophobic expulsion plays an important role in the adsorption of metal ions in the presence of hydrophobic ligands on silica gel surface. Chapter 1. Part II Effects of complexing Ligands on Copper adsorption onto Silica Gel Surface The effect of complexing ligands on the adsorption of Cu(II) was investigated from aqueous solution on silica gel. The ligands used were hydrophobic ionizable organic compounds such as terpyridine, pyridine, lutidine, aminomethyl pyridine, pyridine methanol, and picolinic acid, in...