Adsorption of trace heavy metals: Application of surface complexation theory to a macroporous polymer and a weakly acidic ion-exchange resin

A Hypersol-Macronet polymer, MN-600, and a weakly acidic ion exchanger, C-104E containing mainly carboxylic functionality, have been characterized to evaluate their performance for trace heavy metal removal. Characterization of these polymers in the form of scanning electron micrographs, Brunauer-Emmett-Teller (BET) and Langmuir surface area measurements, Fourier transform infrared spectroscopy analysis, X-ray photoelectron spectroscopy analysis, atomic composition measurement, elemental analysis, sodium capacity determination, and zeta potential measurements has been conducted. Density functional theory has been used to analyze the pore size distribution data of MN-600. The BET and Langmuir surface areas of MN-600 are 951 and 1118 m(2) g(-1), respectively. The zeta potentials of polymers at different pH values indicate zero crossover points at a pH of 1.2 and 1.8 for MN-600 and C-104E, respectively. The sodium capacity values of C-104E and MN-600 are 9.65 and 0.45 mequiv g(-1), respectively. The oxygen content of C-104E is 42.12%, whereas MN-600 contains 15.37% oxygen in the polymer matrix. The higher sorption capacity of C-104E can be attributed to the presence of a greater number of oxygen-containing groups in the polymer (particularly carboxylic functionality). C-104E contains about 1.4% nitrogen, whereas MN-600 contains only 0.47% nitrogen. The applicability of surface complexation theory for the sorption of heavy metals onto these sorbents has been explored. The sorption of copper, nickel, and zinc ions from aqueous solution on these sorbents has been studied in batch equilibrium experiments for binary, ternary, and quaternary systems to determine the equilibrium parameters for modeling of ion-exchange equilibria. From the experimentally determined equilibrium parameters, ion-exchange equilibria have been calculated for a wide range of initial conditions. The experimental results for the Macronet polymer as well as the weakly acidic ion exchanger have been compared with the results obtained using the surface complexation model for the prediction of binary, ternary, and quaternary ion-exchange equilibria.