Ion-exchange kinetics on reactive polymers and inorganic soil constituents

The assessment of the fate (dispersion, retention, degradation), the quantification of transport phenomena, and the relative concentrations of a chemical in the different natural compartments (air, water, soil, and biota) is one of paramount importance in evaluating the chemical 'mobility' in and through different phases. Among others, ion-exchange phenomena at the water-soil interface are of primary importance in soil and environmental chemistry, and research from both thermodynamic and kinetic viewpoints is necessary. With regard to kinetic aspects, despite the huge amount of work performed on reactive polymers, (e.g., ion-exchange resins and/or membranes) insufficient literature in reference to inorganic soil constituents (e.g., clays, oxides, and zeolites) exists. In general, due to the extreme subdivision of the constituent particles of natural exchangers, they are usually considered as 'quasihomogeneous' with the liquid phase. Thus homogeneous kinetic theory can be used to describe their reaction mechanisms. Recent studies have shown that mass transfer phenomena, either in the liquid and/or the solid phase, could play a relevant role in determining general kinetic behavior of these systems in addition to those strictly related to the pure chemical reactions. After a general overview of the basic principles of ion-exchange kinetics on reactive polymers, we shall apply these principles to clays, oxides and zeolites, which serve as models for heterogeneous soils.