Adsorption of Co(ii) and Ni(ii) on beishan granite: Surface complexation model and linear free energy relationship

The adsorption of Co(II) and Ni(II) on crushed Beishan granite (BS03, 600 m) was studied by a batch experimental method. The distribution coefficient (Kd) was found to vary as a function of the pH, ionic strength, and the initial concentrations of Co(II) and Ni(II). In the low pH range, the Kd values of Co(II) and Ni(II) decreased significantly as the ionic strength increased, whereas the effect of the ionic strength was weak in the high pH range. The adsorption of Co(II) and Ni(II) on granite was quantitatively interpreted by a model with one cation exchange reaction and two inner- sphere surface complexation reactions. A linear free energy relationship (LFER) between the equilibrium constants (K) of the surface complexation reactions and the hydrolysis stability constants of the divalent transition metals (OHK) was established. Predictions based on the LFER are in good agreement with the experimental results for the adsorption of Pb(II) and Cu(II) on granite. © Editorial office of Acta Physico-Chimica Sinica.