The equilibrium and fixed-bed study of malachite green
adsorption on chitosan hydrogels
X. H. Song, K. L. Goh and K. Wang
ABSTRACT
Chitosan hydrogel beads were prepared by a precipitation process, on which Q1 the adsorption of
Malachite Green (MG) oxalate was investigated under various conditions. It was found that
adsorption equilibrium was most sensitive to the pH value at pH <8 while fixed bed breakthrough
kinetics presented asymmetric s-shaped profiles which could not be adequately described by
conventional models such as Adams-Bohart and Yoon-Nelson models. The possible reasons were
discussed and an improved model was proposed to better describe the changes in mass transfer
mechanisms during adsorption.
X. H. Song
School of Chemical & Biomedical Engineering,
Nanyang Technological University,
Singapore 618723 Q2
K. L. Goh
School of Mechanical & Systems Engineering,
Newcastle University,
Newcastle Upon Tyne, NE1 7RU,
UK
K. Wang (corresponding author)
Department of Chemical Engineering,
Khalifa University of Science & Technology,
P.O. Box 2533, Abu Dhabi,
U.A.E.
and
Center for Catalysis and Separation
E-mail: kean.wang@ku.ac.ae
Key words | adsorption, breakthrough, chitosan, fixed bed, kinetics, malachite green
INTRODUCTION
Malachite Green (MG) oxalate, a dark green and crystalline
dye, has been widely used in textile, paper and aquaculture
industries (Crini ). Adsorption is a popular technology
for dye removal from dye-containing waste water and is par-
ticularly attractive if the adsorbents are derived from
abundant and low-cost sources. A large number of low-
cost adsorbents have been reported; these absorbents fall
under the following categories: polysaccharides [Chitosan,
cyclodextrin, starch, and their derivatives (Crini ;
Crini et al. ), etc.]; biomass/agricultural wastes [de-oiled
soya (Mittal et al. ), sawdust/weeds (Malik et al. ;
Tarawou & Horsfall Jr ), nut shells (Malik et al. ),
etc.], minerals [clays (Cheknane et al. ), zeolites (Kara-
dag et al. ), oxides (Muliwa et al. )], activated
carbons derived from industrial wastes tyre (Song et al.
), and sludge (Wang et al. ), etc.
Chitosan, the N-deacetylated derivative of chitin (poly
(β-(1 ! 4)-N-acetyl-D-glucosamine), is the second most
abundant natural polymer after cellulose. It has excellent
biodegradability, biocompatibility, non-toxicity, and good
adsorption capacities (Li et al. ). For manufacturing pur-
poses, chitosan may be molded into many desirable shapes,
such as beads, filaments, and membranes. In water treat-
ment, chitosan and its derivatives are widely used as low-
cost adsorbents for the removal of heavy metals, dyes and
other contaminants (Crini ; Li et al. ).
It is generally accepted that the amino groups of chito-
san offer the main adsorption sites for metal ions and
dyes. Amino groups are protonated under acidic conditions
and present strong affinity to these molecules and ions (Xu
et al. ). Chitosan hydrogel beads (grafted or crosslinked)
have been a preferred choice because they have high specific
surface, more exposed free amino groups, and better porous
networks for diffusion.
Several studies have been reported in the literature for MG
adsorption on chitosan. For example, Bekci et al. (Bekçi et al.
) fabricated chitosan beads and studied MG adsorption in
batch mode under different temperature, pH range, and con-
tact time. They found the MG adsorption involved high
activation energy of ∼83 kJ/mol – implicating that the MG
adsorption is a chemical process – with the highest adsorption
capacity (∼93 mg/g) occurring at the optimum pH of 8. The
kinetics were seen to follow the second order rate.
Zheng et al. prepared composite hydrogels using chito-
san, acrylic acid, itaconic acid, and attapulgite (Zheng
et al. ). The hydrogel beads possess an anionic surface
and a 3D porous network, which present good adsorption
capacity towards MG and dyes mixtures. The maximum
1 © IWA Publishing 2019 Water Science & Technology | in press | 2019
doi: 10.2166/wst.2019.160
Uncorrected Proof