Selective ion exchangers crosslinked poly(4-vinyl pyridine) with transition metal ion as

Abstract

Chelating resins are generally used to remove transition metal ions selectively. They are of two types: functionalized resins and templated resins. The selectivity of functionalized resins depends on the pH of the medium, which limits their use in large-scale applications. In contrast, the selectivity of templated resins is not significantly dependent on pH.

In the present work, copper-ion-templated resins with different degrees of crosslinking and one nickel-ion-templated resin have been prepared. They are characterized by ion-exchange capacity (I.E.), elemental analysis, and electron spin resonance (E.S.R.) spectra. Their selectivities for Cu²?, Ni²?, Co²?, Zn²?, and Cd²? have been determined.

The Langmuir sorption model is found to fit the data, and values of the stability constant and saturation constant are calculated. The kinetic behavior of these resins for metal ion sorption is monitored using a recording conductivity meter. The effects of agitation, particle size, solution concentration, and temperature are studied. The unreacted shrinking core model is found to fit the data over a wide range of sorption conditions.

The selectivity of copper-ion-templated resins is high for highly crosslinked resins because of their stable conformational structure. It is observed that the fractional conversion of templated resins increases with increasing concentration and temperature, and with decreasing particle size. The sorption of metal ions is controlled by shell diffusion across all crosslinking contents, particle sizes, solution concentrations, and temperatures employed.

The diffusion coefficients of the different resin–metal ion systems have been calculated using this model. The diffusion coefficient of copper in copper-ion-templated resins (0.941–4.343 × 10?? cm²/sec) lies within the expected range for standard chelating resins. Significantly, the diffusion coefficient for copper ions in crosslinked resins increases with increasing concentration. This phenomenon is discussed in light of similar observations reported for ion-exchange resins in the literature.

The apparent activation energies for diffusion of copper ions in the resin, calculated from Arrhenius-type plots of log D vs. 1/T, are of the order of 10 kcal/mol, in agreement with similar values reported in the literature.