Influence of particle size and salinity on adsorption of basic dyes byagricultural waste: dried Seagrape (Caulerpa lentillifera)
Pimol Punjongharn , Khanidtha Meevasana , Prasert Pavasant
DOI:
Received August 09, 2007,Revised October 23, 2007, Accepted , Available online
Volume 20,2008,Pages 760-768
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Green macroalga Caulerpa lentillifera was found to have reasonable adsorption capacity for basic dyes, Astrazonr Blue FGRL (AB),
Astrazonr Red GTLN (AR), and Astrazonr Golden Yellow GL-E (AY). The initial dye concentration was in the range of 100–1,800
mg/L. The dried algal sorbent was ground and sieved into 3 sizes: S (0.1–0.84 mm), M (0.84–2.0 mm), and L sizes (larger than 2.0
mm). For all conditions examined in this work (at 25℃ in batch systems), the adsorption reached equilibrium within the first hour.
The kinetic data corresponded well with the pseudo second order kinetic model where the rate constant, k2, decreased as the sorbent
size increased for all dyes. The adsorption isotherms followed both Langmuir and Freundlich models. Among three sorbent sizes, S
size gave the highest adsorption capacity followed by M and L sizes. A reduction of sorbent size increased the specific surface area
for mass transfer, and also increased the total pore volume, thus providing more active sites for adsorption. The adsorption of AB was
adversely influenced by the protonation of algal surface at low pH. On the other hand, the adsorption of AR and AY could be due
to weak electrostatic interaction, which was not significantly affected by pH. Increasing salinity of the system caused a decrease in
adsorption capacity possibly due to the competition between Na+ and the dye cations for the binding sites on algal surface. Moreover,
an increase in salinity generated a compressed electrical double layer on the algal surface which exerted repulsive force, retarding the
adsorption of positive charged molecules such as the basic dyes.
