3.13. Desorption and regeneration o

3.13. Desorption and regeneration of adsorbent
The recycling and regeneration ability of adsorbent is important
for the practical application of adsorbent. The adsorbents that have
excellent adsorption capacity as well as high desorption property
are considered as cost effective. Thus, the desorption experiments
were performed to evaluate the recycling ability of EAB. For this,
multiple cycles were run and batch desorption experiments were
conducted at different pH values. Since maximum adsorption took
place under acidic conditions, it was logical that adsorbed dye
molecules can be recovered under basic conditions. Under strong
basic conditions, the number of negatively charged sites on the
sorbent surface favours desorption of dye anions, due to
electrostatic repulsion and the highest desorption efficiency was
found out to be 89% at pH 9 for SR-BA and 82% for SBB-A NaOH
solution. It was observed that the adsorption capacity of both dyes
adsorbed onto EAB adsorbent did not decreased significantly after
each cycle of adsorption–desorption process. Therefore, the EAB
can be employed repeatedly for the adsorption of dyes. An ion
exchange mechanism due to increased adsorption of anionic dyes;
congo dyes (direct dye) in an acidic medium and their increased
desorption in alkaline medium is reported previously [38] and
97.7% desorption of direct red 23 and 93.00% of direct red 80 are
achieved at pH 12 [67], which support the regeneration and
recycling of EAB for environmental application [68,69].
4. Conclusions
The EAB was proved to be effective for the removal of SR-BA and
SBB-A dyes from aqueous solutions. For both dyes, the equilibrium
was reached within 180 and 240 min, respectively. The pH 2,
adsorbent dose 0.1 g, particle size 0.25 and tempearture 303 K were
found best for maxium dyes adsorption. The kinetic was better
described by a pseudo-second-order kinetic model and Freundlich
isotherm
fitted well to the adsorption equilibrium data. The
thermodynamics study revealed that the dyes adsorption onto EAB
was spontanious, favoarable and exothermic process. The functional
groups onto EAB surface such as hydroxyl and carbonyl
group were involved in the adsorption dyes. At optimized
condition, >65% dyes were adsorbed from textile effluents, which
indicates good efficiency of EAB for the adsorption dyes from
textile effluent conatining mixture of dyes.