Counterion exchange kinetics

Aqueous-phase Ni concentration, however, was found to have a pronounced effect on ion exchange kinetics, which is not consistent with prediction from the IPDC model based on the Nernst-Planck equation. Experimental results could, however, be accounted for with the aid of a macroporous model, originally developed by Yoshida and Kataoka based on the assumption of parallel diffusion of counterions in the solid-gel phase and in the macro-... 

Spirodela intermedia, L. minor, and P. stratiotes were able to remove Pb(II), Cd(II), Ni(II), Cu(II), and Zn(II), although the two former ions were removed more efficiently. Data fitted the Langmuir model only for Ni and Cd, but the Freundlich isotherm for all metals tested. The adsorption capacity values (K ) showed that Pb was the metal more efficiently removed from water solution (166.49 and 447.95 mg/g for S. intermedia and L. minor, respectively). The adsorption process for the three species studied followed first-order kinetics. The mechanism involved in biosorption resulted in an ion-exchange process between monovalent metals as counterions present in the macrophytes biomass and heavy metal ions and protons taken up from water.112... 

In the present case, the electron hopping chemistry in the polymeric porphyrins is an especially rich topic because we can manipulate the axial coordination of the porphyrin, to learn how electron self exchange rates respond to axial coordination, and because we can compare the self exchange rates of the different redox couples of a given metallotetraphenylporphyrin polymer. To measure these chemical effects, and avoid potentially competing kinetic phenomena associated with mobilities of the electroneutrality-required counterions in the polymers, we chose a steady state measurement technique based on the sandwich electrode microstructure (19). 

Mixtures of ion-exchanger particles which differ in their kinetic properties are considered next to examine the consequences of such heterogeneity. Eqs. (18) and (19) show that for a given pair of counterions the... 

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