Impact of environmental conditions on the adsorption behavior of radionuclide 63Ni(II) on γ-Al2O3

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by adsorption reactions. The removal of 63Ni(II) from wastewaters by γ-Al2O3 was studied as a function of various environmental parameters such as shaking time, pH, ionic strength, foreign ions, and humic substances under ambient conditions. The results indicated that the adsorption of 63Ni(II) on γ-Al2O3 was strongly dependent on pH and ionic strength. At low pH, the adsorption of 63Ni(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on γ-Al2O3 surfaces, whereas inner-sphere surface complexation was the main adsorption mechanism at high pH. The Langmuir and Freundlich models were used to simulate the adsorption isotherms of 63Ni(II) at three different temperatures of 298.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent adsorption isotherms indicated that the adsorption process of 63Ni(II) on γ-Al2O3 was endothermic and spontaneous.