Mercury Sorption from Aqueous Solution by Chelating Ion Exchange Resins, Activated Carbon and a Biosorbent

Abstract

This paper discusses Hg(II) sorption from aqueous solution onto different sorbents, e.g. a wood-based granular activated carbon (WHK), two commercially available chelating ion exchange resins (Purolite S-920 containing isothiouronium functional groups and Rohm and Haas GT-73 containing thiol functional groups) and a biosorbent (Azolla filicu-loides). These sorbents were characterized using scanning electron microscopy (SEM), determination of nitrogen and amino acid content, BET surface area by N2 adsorption at 77 K, acid=base titration, ion exchange capacity and electrophoretic measurements. Samples were also characterized by energy dispersive spectroscopy and X-ray diffraction after contact and equilibration with mercury solution. These techniques were used in an attempt to elucidate the mechanisms involved in mercury sequestration. The reduction of Hg(II) to Hg(I), i.e. soluble mercuric to insoluble mercurous chloride (Hg2Cl2) on the adsorbent surface, was found to be a controlling reaction mechanism for sorption on granular activated carbon and Azolla filiculoides. Kinetic experiments showed that mercury sorption was rapid on all of the materials. Batch equilibration experiments indicated that Rohm and Haas GT-73 has the highest mercury sorption capacity. Although mercury sorption was studied at elevated concentrations similar to those encountered in industrial effluents, it is suggested that the findings would also apply to final stage water treatment. As a general rule, it was found that mercury (II) removal increased with pH.