Novel bifunctional thio-methylene-pyridine grafted polymeric resin for mercury removal from acidic solutions

This work brings forth a novel porous solid sorbent, thio-methylene-pyridine (TMP) ligand grafted polymeric resin (TMP resin), for selective mercury removal over a wide range of acidity in which the bi-functional group catered to sorption of both cationic and anionic species of Hg^2 + in aqueous hydrochloric acid medium. TMP resin showed quantitative sorption of ‘Hg²⁺’ in high as well as low acidic solutions (chloride medium) with uptake capacity in the range of 70–80 mg Hg/g, indicating sorption of ‘Hg²⁺’ in both cationic and anionic form as (HgCl₄)^2-, hence utilizing the bi-functionality of TMP ligand. Spectroscopic investigation on metal-ligand interactions, as well as DFT calculations indicated towards two separate mechanisms, one being preference for soft-soft co-ordinate complexation at lower acidity and other being anion exchange of Hg-chloride complex by pyridinium group at higher acidity. Near complete back extraction of Hg²⁺ from the Hg-loaded sorbent was achieved using 0.1 M thiourea solution at 0.1 M HCl. Resin was regenerated upto 5 cycles of repeated loading and elution wherein there was no appreciable change in the performance with respect to Hg²⁺ sorption & desorption.