Sedimentation data, processing equilibrium

A few elements—C, N, O, S, Fe, Mn—are predominant participants in aquatic redox processes. Tables 8.6a and 8.6b present equilibrium constants for several couples pertinent to consideration of redox relationships in natural waters and their sediments. Data are taken principally from the second edition of Stability Constants of Metal-lon Complexes and Standard Potentials in Aqueous Solution (Bard et al., 1985). A subsidiary symbol pe (W) is convenient for considering redox situations in natural waters. pe°(W) is analogous to pe except that H" and OH in the redox equilibrium equations are assigned their activities in neutral water. Values for pe°(W) for 25 °C thus apply to unit activities of oxidant and reductant at pH = 7.00. pe°(W) is defined by... 

Applying the foregoing thermodynamic and kinetic information to manganese behavior in natural water systems is considerably limited because the manganese system exemplifies the difficulties discussed earlier. On the thermodynamic side, the kinds of oxide phases in natural waters may not correspond to those for which equilibrium data are available. Also, cation exchange reactions are probably important (21). On the kinetic side, the role of catalysis by various mineral surfaces in suspension or in sediments is not really known. Of considerable importance may be microbial catalysis of the oxidation or reduction processes, as described by Ehrlich (7). With respect to the real systems, relatively... 

Using SigmaPlot 5.0 (Jandel Scientific, San Rafael, CA), the sets of sedimentation equilibrium data for the paucidisperse acetylated methylated and underivatized kraft lignin fractions were successfully curve fit to functions representing sums of terms of the form expressed in Equation (20). In no case were more than four individual terms required for the fits of unprecedented accuracy that were achieved these are exemplified in Figure 6A2 and B2. The sums of the areas under the component exponential curves confirmed that the total mass of solute species observed at equilibrium never differed by more than 1% from that present before the sedimentation process began. 

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