the initial step in the incorporation (1-4). This radioactive Adsorption of Co(II) ions on metal oxides is related to radioacpollution causes an exposure problem to plant workers and tive 60 Co(II) (de)contamination of nuclear power plants, Co(II) results in large amounts of bulky radioactive waste when the ion retention in soils as a plant nutrient, concentration of Co(II) plants are closed after their use. To prevent the radioactive in deep-sea manganese nodules, and other applications. Here, the contamination of nuclear power plants, deionization of coolamount of adsorbed Co(II) on metal oxides was measured as a ing water is carried out, and here inorganic deionizers includfunction of the pH and concentration of Co(II) ions, and the ing metal oxides have advantages over organic ones in heat adsorption properties of metal oxides were evaluated with a model and radioactivity resistance (5). Large amounts of Co(II) that considers simultaneous (1:1) and (1:2) exchange reactions are also concentrated in deep-sea manganese nodules, prebetween Co 2/ aqua ions and surface hydroxyl protons obeying the Frumkin isotherm. The possibility of participation of mono-and sumably through adsorption on iron and manganese oxides polynuclear Co(II) hydroxo complexes in the adsorption was excommon in soils (6-9). The Co(II) retention in soils due amined, and it was suggested that these species play no role under to the adsorption on soil metal oxides is related to soil fertilthe conditions here. From the model parameters, it was found that ity (10-14) and is also critically important when siting and the Co 2/ adsorption ability of metal oxides increases in the order designing repositories for radioactive waste and general Al 2 O 3 Γ΅ Fe 2 O 3 Γ΅ TiO 2 Γ΅ Fe 3 O 4 Γ΅ MnO 2 , showing a good correla-metal waste, since in case of leakage the underground migration to the electronegativity X i of the lattice metal ions of the tion of Co(II) ions may be stopped by such adsorption (15).
oxides. The Co 2/ adsorption was divided into two processes: (1)
To solve problems described above, it is important to deprotonation of surface hydroxyl sites and (2) bonding of Co 2/ know the quantitative Co(II) adsorption properties of metal to the deprotonated sites with a negative charge. With increasing oxides. With knowledge of quantitative properties, it is pos-X i , process 1 increases possibly due to the decrease in the donor sible to design Co(II) adsorption processes and to control electron density responsible for covalent bonds with protons, while process 2 changes only slightly. It was suggested that process 2 is the processes under optimum operating conditions for particdue to ionic bond formation (''electrostatic contact adsorption''), ular purposes. A model of the Co(II) adsorption on metal which is independent of the donor electron density, and the correoxides may be useful for a quantitative evaluation of the lation of the overall process to X i found here was ascribed to properties.
process 1 above. α§ 1997 Academic Press
A number of investigations have been made for modeling Key Words: Co(II) ion; metal oxides; adsorption; electronegativthe adsorption of Co(II) as well as other divalent heavy ity; Frumkin isotherm; modeling. metal ions on metal oxides. Kozawa ( ) studied the ionexchange adsorption of Zn(II) on manganese dioxide, and named the process ''surface chelation.'' The products of