Intraparticle diffusion during selective ion exchange with a macroporous exchanger

Chlorophenols, quaternary ammonium compounds, benzene and naphthalene sulfo nates and benzene carboxylates are examples of environmentally significant synthetic organic compounds which exist as ions in water over a wide range of pH values. This study discusses the sorption kinetics, and more specific ally, intraparticle diffusion behaviors of trace concentrations of pentachl orophenate (PCP-) and other chlorophenates onto a commercially available ma croporous polymeric anion exchanger (IRA-900). The anion exchanger is essen tially biphasic, i.e. every single exchanger particle contains an enormous number of tiny microgels and an interconnected network of pores. Ion exchan ge functional groups reside solely within the microgels. For comparison, a gel or microporous anion exchanger is also included in the study. Experimen tal results reveal a distinctly different type of effect of competing chlor ide ion concentration on gel and macroporous ion exchangers pertaining to s orption of pentachlorophenate (PCP-). While the effective intraparticle dif fusivity of PCP- for gel-type resin remained unaltered with a change in com peting chloride concentration, the same increased significantly for the mac roporous exchanger with an increase in chloride concentration. Pore diffusi on is considered to be the predominant intraparticle transport mechanism fo r highly preferred PCP- inside the macroporous exchanger. Under the normal hydrodynamic conditions of a fixed bed column run, intraparticle diffusion was found to be the rate-limiting step. For various chlorophenates, the eff ective intraparticle diffusivities were inversely correlated to the octanol -water partition coefficients of their parent chlorophenols. (C) 2000 Elsev ier Science B.V. All rights reserved.