AFFINITY DISTRIBUTION DESCRIPTION OF COMPETITIVE ION-BINDING TO HETEROGENEOUS MATERIALS

Semiempirical equilibrium models of competitive, two-component binding of simple ions to heterogeneous materials are based on a combination of independent binding isotherms, such as two-component Langmuir isoth erms or exchange isotherms. Such models are usually sufficiently flexi ble to rationalize various experimental data sets quantitatively. Sinc e such models are thermodynamically consistent, they have substantial predictive capabilities. Furthermore, such models are rather simple, m ay depend on a relatively small number of parameters, and provide an i ntuitive framework for comparison of binding properties of different m aterials. We solve the ill-posed data inversion problem with constrain ed, regularized least-squares techniques. This approach to the interpr etation of two-component competitive ion binding to heterogeneous mate rials is illustrated with two data sets; the binding of Sr2+ and H+ to ferrihydrite (amorphous FeOOH) and that of Cu2+ and H+ to a humic aci d.