1051 the highly selective removal and recovery of uranium from aqueous effluents is essential to mitigate the environmental impact of radioactive contaminations (Li et al., 2019). While various treatment methods, such as chemical precipitation and ion exchange, are currently employed, they often face critical limitations, including high installation costs, limited selectivity, and the generation of hazardous sludge. Consequently, adsorption is increasingly considered a viable alternative due to its ease of operation, broad applicability, and relatively low cost (Liu et al., 2024). In line with circular economy principles and the EU's zero-pollution ambition, there is a growing interest in replacing conventional synthetic sorbents—which are often expensive and toxic—with abundant, eco-friendly "green adsorbents" (EU, 2021). Green adsorbents derived from sustainable sources, such as agricultural waste and biopolymers, utilize waste products to treat hazardous effluents, thereby minimizing secondary pollution (Zemskova & Egorin, 2024; Sahoo et al., 2018). In practice, these materials have proven highly effective at removing radionuclides. For example, modified bentonite clay has demonstrated over 90% removal of U(VI) and Th(IV) (Al-Shaybe et al., 2020), whereas functionalized Moringa seed has achieved uranium removal efficiencies of up to 98% (Hamza et al., 2021). Similarly, biochar produced from garden waste has been shown to effectively remove Caesium-137 by leveraging its porous structure and functional groups, such as carboxyl and hydroxyl groups (El-Naggar et al., 2022). Two promising candidates in the field of waste-based and natural-based adsorbents for radionuclide removal in water treatment processes are chitosan and Moringa Oleifera. Chitosan, a polysaccharide polymer typically derived from crustacean shell waste, is rich in amine and hydroxyl functional groups that exhibit strong coordination affinity for radionuclides (Huang et al., 2017). Meanwhile, Moringa Oleifera seeds— traditionally used for water purification in water-scarce regions—offer a sustainable plant-based alternative. However, although Chitosan is well documented, comparative studies assessing the viability of Moringa Oleifera seeds (MOS) for uranium remediation relative to established biopolymers are limited. This study addresses this gap by investigating the potential of Moringa Oleifera seeds as a sustainable biosorbent for removing uranium from aqueous solutions, comparing their performance with that of Chitosan. Extraction experiments were conducted under controlled conditions to assess adsorption efficiency. Furthermore, the influence of operational parameters, including pH, contact time, uranium concentration, and adsorbent dose, was systematically investigated to optimize the removal process. 2. MATERIALS AND METHODS Moringa Oleifera seeds were obtained from a local farmer in Setúbal, south of Portugal. The Chitosan was obtained from Thermo Fisher Scientific, with a CAS number of 9012-76-4 and a molecular weight of 100.000–300.000, as an off-white to yellowish-beige powder. For the laboratory experiments, the MOS shells were removed. The seeds were then washed with distilled water and dried in an oven at over 100 °C until a constant weight. The seeds were ground into powder using a small coffee grinder. The Chitosan was used as received, without any additional preparation. Two sets of experiments were conducted to assess the ability of Chitosan and Moringa Oleifera to remove uranium from water. Distilled water was spiked with a known concentration of uranium, yielding three 1-L samples at approximately 10, 40, and 400 μg/L. Three batch tests were performed using 1 g of crushed Moringa Oleifera seeds mixed with water containing uranium at different considered concentrations. The extraction steps were performed after 2 and 4 hours of contact time. Each test was conducted in a sealed beaker with continuous mixing. The beaker was then left to settle, and a 100 mL sample was extracted using an air pump from VIDROLAS-VL2 and a 55 mm 1240 filter paper from FILTER-LAB®. The extracted liquid was then poured into a 100 mL plastic bottle. The same procedure was employed for the Chitosan.
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