| Summary: | 博士 === 國立成功大學 === 環境工程學系 === 84 === ABSTRACT Adsorption behaviors among fumarate, maleate and
succinate were compared using the same adsorbent δ-Al2O3 and
initial adsorbate concentrations. Firstly, 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 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 about 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(FCDAs) due
to its molecular flexibility. Secondly, although these FCDAs
can be adsorbed specifically on hydrous δ-Al2O3, the
isoelectric point (IEP) was not observed to shift in the three
adsorption systems studied due to insignificant adsorption near
the IEP and low intrinsic binding affinity of these acids for
the oxide surface. Evidence of low intrinsic affinity arose from
the strong ionic-strength dependence of the adsorption behavior
for each of the three FCDAs. The ionic-strength effects on the
adsorption behavior found for maleate were close to or slightly
stronger than those of succinate, while fumarate exhibited the
strongest ionic-strength dependence among the three FCDAs. These
results were well related to their respective adsorption maxima
(under-saturation) stated above. Therefore, it is suggested
that, under the same experimental conditions, the adsorption of
a particular anion will be attributed to specific adsorption if
the ionic-strength effects of this anion are weaker than any of
the three FCDAs studied. In addition, the lack of a shift in the
isoelectric point can not be used for judging whether the
adsorption is non-specific.
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