Effect of humic acid, fulvic acid, pH, ionic strength and temperature on Ni-63(II) sorption to MnO2

The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide Ni-63(II) to MnO2 have been investigated by using batch techniques. The results indicated that the sorption of Ni-63(II) on MnO2 is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of Ni-63(II) on MnO2 at low pH values, whereas reduces Ni-63(II) sorption at high pH values. The sorption of Ni-63(II) on MnO2 is attributed to inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange. The diffuse layer model (DLM) is used to simulate the experimental data well with the aid of FITEQL 3.2. The thermodynamic parameters (Delta H-0, Delta S-0, Delta G(0)) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of Ni-63(II) on MnO2 is a spontaneous and endothermic process.