Removal of iodide from aqueous solutions by polyethylenimine-epichlorohydrin resins

The iodide removal from aqueous solutions (initial I--concentration: 300-5,000 mg/L) by a low and a high molecular weight polyethylenimine-epichlorohydrin resin was investigated both in absence and presence of background electrolytes (NaCl and Na2SO4, ionic strength due to background electrolyte 0.1 M) using a batch technique, I-131 as radioactive tracer and high-resolution gamma-ray spectrometry. The experiments in absence of background electrolyte were performed using solutions of initial pH 3 and 7, whereas those in presence using solutions of initial pH 3. The results, which demonstrated the high iodide-removal efficiency of both resins, were modeled using the Langmuir and Freundlich isotherm equations. The experimental data were better reproduced using the Langmuir equation. Using this equation maximum sorption capacity values (Q (max)) of 638.8 and 603.3 mg/g were obtained for the high molecular weight resin from solutions of initial pH 3 and 7 respectively, whereas the corresponding values for the low molecular weight one were slightly lower (552.4 and 507.5 mg/g respectively). The iodide uptake by the resins strongly depended on the presence of competing anions and especially of sulfates. The examination of sections of the I-loaded resins grains by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) revealed that iodine was evenly distributed throughout the bulk of the resins and not only bound to their surface.