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Desorption of tetracycline from montmorillonite by aluminum, calcium, and sodium: an indication of intercalation stability
Chang, P.-H.; Li, Z.; Jean, J.-S.; Jiang, W.-T.; Wu, Q.; Kuo, C.-Y. & Kraus, J.
Abstract
As the uptake of cationic drugs, such as tetracycline
(TC), was attributed to cation exchange, the stability
of adsorbed TC on a Ca-montmorillonite SAz-2 was
studied using cationic solutions of different valence charges
under different pH conditions. At the initial loading of
356 mg g-1, the amounts of TC desorbed by 0.05 M
AlCl3, CaCl2, and NaCl were 133 ± 4, 83 ± 6, and
50 ± 4 mg g-1, respectively, or 37, 23, and 14 %. However,
when the amount or percentage of TC desorbed was
normalized to the equivalence of each cation, the values
were in the range of 44–50 mg g-1 or 11–14 % per
10 mmol of charge. The kinetics of TC desorption were
moderately fast and almost reached equilibrium in 6 h. The
results followed the pseudo-second-order kinetic model
with reaction rate in the order of AlCl3>CaCl2>NaCl at
a higher initial TC loading level. The total amount of TC
desorbed after five desorption cycles followed the order of
AlCl3>CaCl2>NaCl, too, suggesting that cations with
higher positive charges, thus, less hydrated, are preferred to
remove adsorbed cationic drugs. The FTIR analyses
showed larger band shift when Al3+ was used as the
desorbing reagent. The XRD patterns before and after TC
desorption revealed no changes in basal spacing, even after
five desorption cycles, suggesting that the removal of TC
from SAz-2 was largely from the external surfaces.
Keywords
Ca-montmorillonite; Cation exchange; Complexation; Desorption; Metal cations; Tetracycline
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