الفهرس 
Biological adsorption methodsOnly 14 pages are availabe for public view
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Abstract
The widespread presence of radioactive uranium and other heavy metals in
the environment due to natural and human activities, which has led to water
and environmental contamination. Various techniques have been used to
remove uranium and other toxic heavy metals from liquid solutions, with
biological adsorption being a particularly effective method. Recent
developments have focused on using biopolymers like chitosan, especially
fungal chitosan, due to their cost-effectiveness, renewability, and superior
performance in metal remediation compared to other materials. However,
chitosan has limitations, such as a small specific surface area and poor
mechanical strength. To overcome these limitations, researchers have
developed modified biosorbents with higher metal sorption performance,
primarily due to their increased specific surface area and improved impurity
removal.
In the present study, the results obtained can be summarized as follows:
In our screening process, we determined that the maximum fungal biomass
dry weights were achieved by A. flavus, A. niger, and A. clavatus, which
belong to the class Ascomycetes reaching 18.5 g/L, 14.6 g/L, and 15.0 g/L,
respectively, after 7 days.
In the investigation, it was found that the highest dry weight production for
A. flavus occurred with yields of 18.5 g/L at pH 5 and a temperature of 30
°C during a 7 days incubation period. Additionally, glucose and potassium
nitrate (KNO3) were used as the carbon and nitrogen sources.
A. flavus was undergo deproteinization and deacetylation, followed by
extraction, precipitation, and centrifugation. The crude fungal chitosan was
washed with distilled water, 96% ethanol, and 4% acetone, and then dried
from 20 to 100ºC. The fungal chitosan was thereby obtained. This finding
suggests that A. flavus can be effectively used to produce environmentally
friendly chitosan biopolymer with a yield of 13.48%.
The fungal isolate A.flavus was identified based on colony morphology and
microscopic observation and confirmed by PCR amplification through
agarose gel electrophoresis.
The chitosan derived from Aspergillus flavus (AFC) was characterized using
(FTIR). The degree of deacetylation (DDA) was determined to be 80% based
on the degree of acetylation (DA) and deacetylation (DDA) equations.
The Aspergillus flavus chitosan (AFC) submit to a subsequent modification
process by coating its particles with a polystyrene shell. This step aimed to
improve the efficiency of the resulting composite structure (P-AFC).
Following that, another modification was performed on P-AFC by loading
it with cobalt and aluminum hydroxide nanoparticles producing
nanocomposite named as (PNC-AFC) to enhance its adsorption properties.
The characterization of the prepared fungal chitosan (AFC) and its based
composites, P-AFC and PNC-AFC, involved the use of various analytical
techniques, including (FTIR), (ESEM), (BET), and (DLS) analyses.
The study investigated the biosorption efficiencies of U(VI) from a synthetic
solution found to be 23.7% for AFC, 82.8% for P-AFC, and 92.0% for PNCAFC.
Notably, the optimal conditions were: a pH was 4, contact time of 60
minutes and a chitosan dosage of 0.5 g/L and 50 mg L-1 as an initial U(VI)
concentration.
Based on the correlation coefficient (R2), the U(VI) biosorption results by
fungal chitosan and its based composites fit well with the pseudo-secondorder
and Langmuir models.
ate the spontaneous nature of
surface.
The use of 0.5 M HNO3 as the desorbing agent resulted in a 94.4%
desorption of uranium ions. To assess the reusability of the (PNC-AFC)
sorbent, the adsorption desorption experiment was repeated five cycles. The
sorption and desorption percent slightly changed from 92.0 to 87.5% for
sorption process and from 94.0 to 88.5% for desorption process over the five
cycles.
In another application, the highly efficient adsorbent PNC-AFC is utilized
to optimize cadmium adsorption. The results reveal that at pH 7, with a
contact time of 60 minutes, an adsorbent dosage of 0.5 g/L, and an initial
Cd(II) concentration of 50 mg/L, the most optimum conditions for cadmium
adsorption efficiency are achieved, reaching nearly 78% from aqueous
solutions at 25°C. In terms of kinetics, the pseudo-second order model is the
best fit, and the Weber-Morris model suggests that Cd(II) ions’ sorption with
PNC-AFC is governed by multiple mechanisms. When analyzing
equilibrium isotherms, the Langmuir model provides a better fit than the
Freundlich model, indicating a monolayer coverage by PNC-AFC sorbent.
Thermodynamically, the process is endothermic, spontaneous, and increases
randomness at the sorbent surface.
In the context of cadmium elution and biosorbent (PNC-AFC) reusability,
the study revealed that sulfuric acid yielded the highest elution efficiency at
95.3%. Over five cycles, there was only a slight decrease in both biosorption
and desorption percentages, shifting from 79.2% to 74.5% and from 95.0%
to 90.2%, respectively.
In the case study using PNC-AFC biosorbent for liquid raffinate treatment,
several observations were made. Calcium and sodium ions had low removal
efficiency, at approximately 5.5% and 3.8%, respectively. Iron
concentration was reduced by about 15.0%. Copper (Cu) exhibited a high
sorption efficiency, reaching around 95.0%, while zinc (Zn) had an
efficiency of about 74.0%. As for the target metal ions, uranium (VI) and
cadmium Cd(II) ions, their uptake percentages were notably high, at
approximately 89.7% and 75%, respectively.