Ethyleneimine (etn) has been covalently bonded onto silica gel via homogeneous (SiSN1) and heterogeneous (SiSN2) routes. Both synthesised silica gel surfaces have been applied to adsorb divalent cations from aqueous solution at room temperature. The series of isotherms of adsorption were adjusted to a modified Langmuir equation, after collecting the data from the solid/MCl₂ solution (M = Co, Ni, Cu, Pb and Hg) interfaces. The maximum adsorption were 1.08, 1.20, 1.70, 1.34 and 4.02 mmol g⁻¹ for SiSN1 and 0.72, 1.74, 1.91, 2.19 and 2.89 mmol g⁻¹ for SiSN2, for a the sequence of divalent cations: Co, Ni, Cu, Pb and Hg, respectively. Columns loaded with immobilised silica show resolutions (R) for separating metal ion couples: R_Co–Ni = 0.22, R_Co–Pb = 0.76, R_Co–Cu = 1.12, : R_Co–Hg = 2.06, R_Ni–Pb = 0.50, R_Ni–Cu = 1.17, R_Ni–Hg = 2.38, R_Pb–Cu = 0.33, R_Pb–Hg = 1.83 and R_Cu–Hg = 1.60 for the SiSN1 surface. The sequence: R_Co–Ni = 1.10, R_Co–Pb = 1.44, R_Co–Cu = 1.63, : R_Co–Hg = 2.26, R_Ni–Pb = 0.08, R_Ni–Cu = 0.33, R_Ni–Hg = 1.40, R_Pb–Cu = 0.38, R_Pb–Hg = 1.82 and R_Cu–Hg = 1.55 was determined for SiSN2.