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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. |