Adsorption of heavy metal ions from aqueous solutions by amine and carboxylate functionalised bentonites

Amine and carboxylate functionalised bentonites were used as adsorbents of heavy metal ions (Pb(II), Hg(II) and Cu(II)) from aqueous solutions. 3-aminopropyl trimethoxysilane was grafted on sodium bentonite (Bent), and this amine functionalised bentonite (BentNH2) was converted into a carboxylate functionality (BentCOOH) by reaction with succinic anhydride. Both adsorbents were characterised by FTIR, XRD, TG/DTG, SEM and elemental analyses. Both adsorbents showed maximum adsorption of the metal ions at pH 5.0–6.0. The adsorption processes followed pseudo-second-order kinetics. The Freundlich model best fitted the adsorption data. The metal ions were mainly bound by complexation on BentNH2 and on BentCOOH by ion exchange and complexation. The regeneration of the adsorbents was tested by repeated adsorption–desorption studies.