Selective adsorption of Pb(II) and Hg(II) on melamine-grafted chitosan

Amine groups can play significant roles in modified chitosans for adsorption of heavy metal ions. A novel chitosan modified adsorbent (GMCS) grafted with lots of amine groups was synthesized by using glutaraldehyde as a crosslinker between chitosan and melamine. The structure and morphology of GMCS was characterized using FT-IR, ¹³C NMR, elemental analysis, XRD, TGA, SEM, BET and zeta potential analysis. The adsorption of GMCS and chitosan for different heavy metal ions was compared. The results indicated that GMCS had higher selectivity and uptake for adsorption of Pb²⁺ and Hg²⁺ than chitosan. Effects of some variables for uptakes of Pb²⁺ and Hg²⁺ on GMCS were studied. The kinetic and isothermal results showed that the adsorption followed the pseudo-second-order kinetic and Langmuir isotherm models. The adsorbent had highest adsorption capacity of 618.2 mg/g and 490.7 mg/g at pH 5 and 6 for Pb²⁺ and Hg²⁺, respectively. The adsorption was an endothermic and spontaneous chemical process. Five cycled experiments of adsorption-desorption showed that the adsorbent could be efficiently regenerated.