Impact of environmental conditions on the sorption behavior of radionuclide 60Co(II) on MnO2

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The removal of 60Co(II) from wastewaters by MnO2 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 sorption of 60Co(II) on MnO2 was strongly dependent on pH and ionic strength. At low pH, the sorption of 60Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on MnO2 surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA/FA enhances 60Co(II) sorption at low pH values, whereas reduces 60Co(II) sorption at high pH values. The Langmuir and Freundlich models were used to simulate the sorption isotherms of 60Co(II) at three different temperatures of 298.15, 318.15 and 338.15 K. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature dependent sorption isotherms indicated that the sorption process of 60Co(II) on MnO2 was endothermic and spontaneous.