A new guar gum-based adsorbent for the removal of Hg(II) from its aqueous solutions

• A new bioadsorbent was synthesized from oxidized crosslinked guar gum and hexamethylenediamine.
• Bioadsorbent was used for the removal of Hg(II) ions from its aqueous solutions.
• A high maximum adsorption efficiency of 41.13 mg/g was obtained.
• Bioadsorbent was reusable up to five cycles unlike Schiff-bases those are unstable.
• Adsorption data fits second order kinetics and Freundlich isotherm.

Modification of biopolymers by oxidation is an easy process to develop effective adsorbents for the removal of toxic metal ions from their aqueous solutions. In the present study, guar gum (GG) was crosslinked with epichlorohydrin and then oxidized to the polydialdehyde form (GG-clPDA). The latter was converted to a Schiff-base, GG-clCHN(CH2)6NCHGG, by reaction with hexamethylenediamine. Different forms of the modified GG were characterized by SEM, FTIR and XRD and investigated as adsorbents for the removal of Hg(II) ions from their aqueous solutions. The adsorption process was carried out through the variation of time, temperature, pH and initial concentration of Hg(II) ions. GG-clCHN(CH2)6NCHGG was observed to be an efficient adsorbent with a maximum adsorption capacity of 41.13 mg/g. It is reusable up to five cycles at the optimum conditions obtained for the maximum ions uptake. The kinetic data generated fit the Freundlich isotherm and pseudo-second order kinetics.