Chromium(VI) removal from aqueous solutions using a polyethylenimine–epichlorohydrin resin

The ability of the synthesized polyethylenimine–epichlorohydrin resin to remove Cr(VI) from aqueous solutions was investigated in the absence (initial pH 2–7) and presence of background electrolytes (NaNO3 and Na2SO4 solutions of initial pH 3 and 6). The determined Cr uptake was significantly higher than the one reported for the majority of other sorbents. The photo­met­rically determined uptake data were modeled by the Langmuir, Redlich–Peter­son, Langmuir–Freundlich and Toth equation. The modeling results did not indicate any preference to one specific model in terms of the goodness-of-fit and the prediction of maximum sorption capacity. The Cr-sorption kinetics were investigated at 15, 25, 35 and 45 °C using 51Cr-labeled solutions and γ -ray spectroscopy. The Cr-sorption was very fast at all studied temperatures and well reproduced by the pseudo-second order kinetics equation. The rate constant and activation energy values were calculated using the experimental data. The Cr-loaded resin was also examined by XRD, XPS, XAFS and SEM/ /EDS. The XPS and XAFS investigations indicated a partial reduction of Cr(VI) to Cr(III). The environmental compatibility of the Cr-loaded resin was examined using the EPA-TCLP method. The Cr-binding by the resin was very stable and regeneration attempts with HCl solutions of pH 3 were rather unsuc­cessful.