dc.description.abstract |
Heavy metal pollution is a serious problem to aquatic ecosystems because some of
these metals are potentially toxic even at very low concentrations. Chitosan, a
biopolymer produced from crustacean shells, has applications in various areas,
particularly in drinking water and wastewater treatment due to its ability to remove
metallic ions from solutions. The purpose of this research work was to study the
adsorption of cadmium and lead ions into chitosan, produced from shrimp shells at
the laboratory level. Shrimp type “penaeus monodon” (giant tiger prawn) was used
to synthesis the chitosan. The main characteristic properties such as degree of
deacetylation (DD); the amount of amine groups in chitosan, viscosity, crystallinity
and thermal analysis were done by using Fourier transform infrared spectroscopy,
Brookfield viscometer, X-ray spectroscopy, thermo gravimetric analysis (TGA) and
differential thermal analysis (DTA). Chitosan, with a degree of deacetylation
between 80%- 95% was used in the experimental part and the flake sizes were
smaller than 0.25mm. Experimental work involved the determination of the
adsorption isotherms and kinetic studies for each metallic ion in a batch system.
Effect of Degree of deacetylation (DD) of the chitosan, effect of initial pH of the
metal ion solution, effect of particle size, effect of initial heavy metal concentration,
and effect of chitosan dosage were studied. The results showed that the adsorption
capacity depends strongly on pH of the solution, DD of chitosan and slightly
depends on the particle size. According to the results, pH values at 6.5 for cadmium
and pH values at 4.5 for lead show higher adsorption capacity. High DD chitosan
showed higher adsorption capacity mainly due to the higher number of active amino
groups in high DD sample.
Simplified kinetic models such as pseudo-first-order, pseudo-second-order, Elovich
model and intra-particle diffusion model were used to determine the rate limiting
step. Both linear and non-linear According to the kinetic models pseudo second
order model best described the adsorption process. Both linear and non-linear models
and Elovich model best described the adsorption process. Multilinearity in the
intraparticle diffusion model suggested that the adsorption of heavy metal consists of
two major steps, due to the different pore sizes of chitosan.
Equilibrium experimental data were analyzed by using two different isotherm
models namely, Langmuir and Freundlich. According to the results, adsorption
process of cadmium and lead heavy metals is heterogeneous and multilayer
adsorption as it best fit with the Freundlich isotherm model. According to the
thermodynamic experiments, adsorption process is favorable and physical adsorption
was predominant in the adsorption process. Desorption of the heavy metals was
possible by using different regeneration solutions. |
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