| dc.description.abstract | Chelating resins are generally used to remove transition metal ions selectively. They are of two types: functionalised resins and templated resins. The selectivity in the former case is dependent on the pH of the medium, which limits its use in large scale applications. The selectivity of templated resins, however, is not significantly dependent on pH.
In the present work, copper ion templated resins of different degrees of crosslinking and one nickel ion templated resin have been prepared. They are characterised by I.E., elemental analyser, and E.S.R. spectra. Their selectivities for Cu² , Ni² , Co² , Zn² and Cd² have been determined. The Langmuir sorption isotherm is found to fit the data; the values of the stability constant and the saturation constant are calculated. The kinetic behaviour 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 fairly wide range of sorption.
The selectivity of the copper ion templated resins is high for the highly crosslinked resins because of their stable conformational structure. It is observed that the fractional conversion of the templated resins increases with increasing concentration, increasing temperature, and decreasing particle size. The sorption of metal ions is controlled by shell diffusion for 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 the 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 ion in the 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 ion in the resin, calculated from an Arrhenius type plot of D vs. 1/T, are of the order of 10 kcal/mol, in agreement with values reported in the literature. | |
