Kurbatov plot

In a simplified form Eq. (ii) was used, decades ago, to assess metal ion adsorption to surfaces, by plotting log ([Meads] / [Me2+]) vs pH. (Kurbatov et al., 1951). The slope of this curve gives an idea on n. The model for this "Kurbatov-plot" assumes that the adsorbent =S is present in large excess and that the adsorption at constant pH is not affected by surface charge. Fig. 2.11 gives an example for the binding of metal ions to amorphous Si02. 

The Kurbatov plot is a convenient tool to display in a simple way adsorption (surface complex formation) data. But care must be exercised in the interpretation of the data, because n varies with pH and may vary with the adsorption coverage. For an exact analysis of the proton release stoichiometry, see Hohl and Stumm (1976) or Honeyman and Leckie (1986). 

To what extent are assumptions of a constant x valid Table II shows the observed macroscopic proton coefficients for cation and anion adsorption in a variety of heterogeneous systems. The coefficients were determined by Kurbatov plots ( 6) or by isotherm analysis ( 7), unless otherwise indicated. In all cases, x is not an integer. 

Kurbatov Plots. Kurbatov plots (6) are made by applying the linearization of a general overall mass action expression (e.g. Equation 4)... 

Figure 3. a) Cd(II) fractional adsorption onto o-alumina as a function of pH and site concentration b) Kurbatov plots of the Cd(II)/a-alumina system. 

Kurbatov plots (jj ) have often been employed to determine the net metal ion/proton exchange, x> from adsorption data. Although Kurbatov constants are convenient curve-fitting parameters, they are insensitive to the variation of x with pH and adsorption density and should be dispensed with for use in adsorbate partitioning calculations, particularly when high adsorption densities are expected ( 9 ). 

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