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

Abstract The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide 63Ni(II) to MnO2 have been investigated by using batch techniques. The results indicated that the sorption of 63Ni(II) on MnO2 is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of 63Ni(II) on MnO2 at low pH values, whereas reduces 63Ni(II) sorption at high pH values. The sorption of 63Ni(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 (ΔH 0, ΔS 0, ΔG 0) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of 63Ni(II) on MnO2 is a spontaneous and endothermic process.