Multistage Optimization of the Adsorption of Methylene Blue Dye onto Defatted Carica papaya seeds
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Date
2009-07-01
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Abstract
Carica papaya seeds were defatted and used for the adsorption of methylene blue dye (MB dye). The
pHPZC and specific surface area (SSA) of the defatted and undefatted Carica papaya seeds were found to be
6.25 and 143.27 m2 g−1 respectively. The adsorption capacities of the defatted Carica papaya seeds were
1250 and 769.23 mg g−1. Fourier transformed infrared (FT-IR) spectra analysis of defatted seeds suggests
the presence of , -unsaturated ketone, -keto (enolic) esters and lactones, quinones and carboxylic
acids which were absent in the undefatted sample. The presence of carboxylic acid, phenolic and lactone
functional groups were confirmed by surface chemistry studies. Adsorption of MB dye onto DPS adsorbent
was found to be exothermic and spontaneous. FT-IR spectra of various particle sizes indicate the presence
of functional groups on every particle size necessary for the adsorption of MB dye.
Pseudo-second-order kinetic rate constant increased with increasing initial MB dye concentration. The
adsorption reaction was observed to be very fast perhaps because of the presence of multiple functional
groups with some of them having lone pair of electrons. Increasing pH was observed to have very little
positive effect on the adsorption of MB dye on DPS adsorbent. Increasing particle size decreased the
adsorption capacity of DPS adsorbent for MB dye. It is suggested that the mechanism for the adsorption
of MB dye onto DPS adsorbent might not only be solely controlled by film diffusion but also by pore
diffusion.
Mathematical models for the optimization of adsorbent dose, number of adsorption stages and mini mum contact time were developed. The optimum conditions for the adsorption of 99% of 100 mg L−1 MB
dye from 10 m3 of aqueous solution of the dye were five adsorption stages, ≈21 kg for each stage with a
total minimum contact time of ≈71 min
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Keywords
Surface chemistry, Kinetic rate, Carica papaya, Optimization, Adsorption stages, Methylene blue