Chromium(III) removal by epoxy-cross-linked poly(ethylenimine) used as gel-coat on silica .1. Sorption characteristics

Poly(ethylenimine) has been gel-coated on high surface area silica and insolubilized by crosslinking with a low molecular weight diepoxide (epoxy equivalent 180 g). The resulting granular sorbent shows several times higher sorption than the commercial chelating resin Chelex-100 in chromium(III) sorption from sulfate solution, the respective saturation capacities being 3.2 and 0.95 mmol of Cr(III)/g of dry resin. The sorption of Cr(III) from its chloride solution is less on both the resins, the saturation levels being 0.62 and 0.78 mmol/g of dry resin, respectively. The sorption of Cr(III)/Cl- on both these sorbents is, however, enhanced significantly by NaCl, the effect being more marked for the gel-coated resin, which shows more than 100% increase in Cr(III) sorption from 0.5 M NaCl solution containing Cr(III) in low concentrations. Both the gel-coated PEI and Chelex-100 show fast kinetics, the t(1/2) values in Cr(III) sorption being 45 and 30 s, respectively. However, the Cr(III) sorbed on Chelex-100 cannot be stripped at ambient temperature even with concentrated HCl while, in contrast, the gel-coated PEI is stripped very easily, the tilt value in 4 N HCl being only 25 s.