Figure 6.

SEM images (magnification 2 kx) of chitosan surfaces (a) natural chitosan flake; (b) natural chitosan flake after the storage for 24 h in water and followed by air drying; (c) and (d) after adsorption of nickel ions from nickel nitrate solution with initial nickel ion concentration of (c) 35 mg·L⁻¹ Ni²⁺ and (d) 350 mg·L⁻¹ Ni²⁺; (e) and (f) after adsorption of nickel ions from nickel sulfate solution with initial nickel ion concentration with (e) 35 mg·L⁻¹ Ni²⁺ and (f) 350 mg·L⁻¹ Ni²⁺. The contact time of chitosan with nickel solutions was 24 h.