Fig. 1. σ_H (C/m²) vs. pH curves of RB in NaCl solutions: triangles, 1.0 M; squares, 0.1 M; circles, 0.01 M.

Fig. 2. σ_H (C/m²) vs. pH curves of AAB in NaCl solutions: triangles, 1.0 M; squares, 0.1 M; circles, 0.01 M.

Fig. 3. The XRD patterns of the RB (a) and AAB (b) (M: montmorillonite).

Fig. 4. The XRD patterns of the Cu-RB (a) and Cu-AAB (b) (M: montmorillonite).

Fig. 5. IR spectra of the RB (a), AAB (b), Cu-RB (c), and Cu-AAB (d).

Fig. 6. Thermal analysis curves of the RB (a), AAB (b), Cu-RB (c), and Cu-AAB (d).

Fig. 7. Linear plots of Langmuir isotherms of Cu(II) adsorption on bentonite samples: circle, RB; squares, AAB.

Fig. 8. Linear plots of Freundlich isotherms of Cu(II) adsorption on bentonite samples: circle, RB; squares, AAB.

Fig. 9. Adsorption of Cu(II) (0.6 μM) by (a) RB and (b) AAB (3.3 g L⁻¹) as function of pH and ionic strenght (IS) (controlled by KNO₃): squares, 1.0 M; diamonds, 0.1 M; triangles, 0.05 M; circles, 0.02 M.

Fig. 10. Adsorption of Cu(II) (0.6 μM) by (a) RB and (b) AAB (3.3 g L⁻¹) as function of pH and in the presence of Cl⁻, SO₄²⁻, and PO₄³⁻ [ionic strenght (IS) is 0.1 M (KNO₃); circles, PO₄³⁻; squares, SO₄²⁻; triangles, Cl⁻].

Chemical composition of the samples

d-Spacing and relative intensity for bentonite samples

Adsorption isotherm constants for the adsorption of Cu(II) onto bentonite samples (q_m: mmol/g, K_L: L/mol, K_f: mmol^(1−1/n) L^1/n/g)

Thermodynamic parameters for the adsorption of Cu(II) onto bentonite samples