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Self-consistent field theory for adsorption and association is utilized to calculate the adsorption of an ionic surfactant (C16P3(sub +)) to two identical, negatively charged, slightly hydrophobic solids separated by a thin film and immersed in an infinite reservoir of aqueous 1:1 electrolyte. The consequence of findings is described in the context of experimental studies of interaction forces and images of adsorbed structures with atomic force microscopy.

Self-consistent field theory for adsorption and association is utilized to calculate the adsorption of the ionic surfactant (C16P3(super +)) on two neutral, slightly hydrophobic solids separated by a thin aqueous film and immersed in an infinite reservoir of aqueous 1:1 electrolyte. The change in surfactant adsorption as a function of the separation between the solids is discussed in relation to the forces between the solids as well as the shape of the adsorption.

The absorption of humic acids on iron oxide-coated silicon plates were shown to be dependent on pH, with a decrease in pH increasing humic acid absorption. Desorption was achieved either through a change in pH with no corresponding change in the concentration of the humic acid or upon dilution with no corresponding change in pH. Desorption using the change in pH was found to be reversible, with additional increases in pH accelerating the desorption process.

A model for ion binding to humic substances was developed through the combination of the non-ideal competitive adsorption (NICA) model for specific binding of electrolyte ions with a Donnan-type model for nonspecific binding. The resulting NICA-Donnan model was applied to data for H, Ca, Cd, Cu and Pb binding by a purified peat humic acid. Predictions of the competitive effect of Ca on Cd and Cu binding at various pHs were consistent with experimental data, except for some small differences. The increase in Cd and Cu binding on changing from a 0.1 M KNO3 background electrolyte to 0.01 M KNO3 was also predicted well by the NICA-Donnan model.

The non-ideal competitive adsorption model was developed to describe the competitive binding of metal ions by humic acids in a chemically heterogeneous system. It was used to describe the binding of hydrogen, calcium, copper and cadmium ions on a purified peat humic acid. The results showed that the model fits the data well over a wide range of free metal ion concentrations and pH range, indicating that the binding of metal ions to humic acids is a function of the effects of ion-specific non-ideality and the chemical heterogeneity of humic material.

Different semianalytical methods to determine the affinity distribution functions may be used to derive f(log K) from experimental binding data only if the error problem has been accounted for. The condensation approximation method is ideal for poor data, while the logarithmic symmetrical approximation with the second-order affinity spectrum method is useful for high-quality data. A smoothing spline technique is suitable in determining the derivatives of a binding curve essential to describe the distribution function. The generalized cross-validation technique combined with physical constraints is recommended to unarbitrarily establish the smoothing parameter.

The local decay function approximation-G2 (LODA-G2) for the determination of rate constant distribution functions was used to re-analyze copper-humate dissociation data on humic material from various sampling points in the Ogeechee River, GA. A smoothing spline procedure was applied to the data to explain the experimental error. The appropriate smoothing parameter was taken based on the generalized cross-validation technique adapted to the problem.

Derivatives of the overall adsorption isotherm are subjected to binding heterogeneity analysis to determine the affinity distribution function. Ionic strength due to electrostatic effects determined the apparent affinity distribution. These electrostatic effects were described by a double layer rigid sphere model. The resulting affinity distribution is described by a pair of semi-Gaussian peaks.

Local isotherm approximation (LIA) and differential equilibrium function (DEF) can be used to calculate the affinity of ions to bonding with heterogeneous ligands. LIA methods use estimates of local binding functions to compute the distribution function. This results in a flattened distribution curve. The DEF method uses the law of mass action and produces distribution curves that are asymmetrically distorted.