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

Abstract

Abstract The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide 63 Ni(II) to MnO 2 have been investigated by using batch techniques. The results indicated that the sorption of 63 Ni(II) on MnO 2 is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of 63 Ni(II) on MnO 2 at low pH values, whereas reduces 63 Ni(II) sorption at high pH values. The sorption of 63 Ni(II) on MnO 2 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 (Δ H 0 , Δ S 0 , Δ G 0 ) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of 63 Ni(II) on MnO 2 is a spontaneous and endothermic process.