Adsorption behaviors among fumarate, maleate, and
succinate were compared using the same adsorbent
δ-Al2O3 and initial adsorbate concentrations.
The adsorption maxima were found all near the
midpoint
of their respective two pK values indicating that the
adsorption of HX- was more favorable than
adsorption
of H2X and X2- and the adsorption densities
were significantly influenced by the electrostatic
microenvironment. The adsorption maxima of maleate were about 10%
higher than those of fumarate but
close to or slightly less than those of succinate before saturation was
approached. However, when the
adsorbent surface became crowded, the saturated adsorption maxima of
maleate and succinate were ca.
1/3 and 1/2, respectively, higher than that of fumarate, indicating
that the trans-form isomer occupied
more binding space than the cis-form and the single bond
anion (succinate) occupied the least binding space
among the three four-carbon dicarboxylic acids due to its molecular
flexibility.