1052 The solution's pH was finally adjusted to 1.7 to preserve the samples and avoid precipitation. The samples were then sealed and left to settle for further testing of the final uranium concentration in the extracted liquids. The liquid extractions from the experiments were further prepared in accordance with ISO 13169:2018 at the Laboratory of Natural Radioactivity in Coimbra (LRN). Water samples were acidified with nitric acid to a pH of 1.7 ± 0.2, after which a complexing agent [bis(2-ethylhexyl) hydrogen phosphate, HDEHP] and the scintillation cocktail Optiscint (Revvity) were added. The mixture was stirred and left to stand until phase separation occurred between the aqueous layer and the less dense scintillation cocktail. The scintillation phase was collected in a vial and analyzed by liquid scintillation counting with the Quantulus 1220 and Quantulus GCT 6220 counters (Revvity). Process efficiency was determined using a naturaluranium standard supplied by the Czech Metrology Institute. 3. RESULTS The Chitosan (CS) used in this experiment was unmodified. As noted by Xu et al. (2015), unmodified Chitosan often yields limited results; however, chemical modification can alter its functional groups, significantly increasing its removal efficiency. Also, Shi et al. (2024) used CaCO3-Doped Chitosan modified with PO43– to effectively remove uranium from water. A recent study by Xin et al. (2025) highlights the use of Metal-Organic Frameworks (MOFs) functionalized with Chitosan for effective uranium adsorption. In the experiments, Chitosan formed a viscous slurry upon mixing, which affected filtration efficiency, even after vacuum filtration. The obtained results are presented in Table 1, along with the percentage of removal. Table 20 - Initial and final concentration of uranium after batch experiments with Chitosan Initial [U] (µg/L) Final [U] (µg/L) Contact time (h) Removal (%) Uncertainty (µg/L) 8 5.65 2 29.34 2.87 8 5.23 4 34.68 2.74 373 304.37 2 18.40 36.37 373 270.46 4 27.49 34.10 38 26.44 2 30.43 4.56 38 30.89 4 30.89 4.91
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