Uranium Removal from Water Using Moringa oleifera and Chitosan: A Comparative Biosorption Study

This study evaluated the baseline performance of unmodified Moringa oleifera seeds and crustacean-derived chitosan for uranium removal from aqueous solutions relevant to naturally occurring radioactive material (NORM) contamination. Batch adsorption experiments were conducted using uranium-spiked solutions with nominal concentrations of 10, 50, and 500 µg/L (measured baseline concentrations of 8, 38, and 484 μg/L). A Taguchi L27 fractional factorial design was applied to optimize uranium biosorption parameters for M. oleifera seeds, while chitosan was assessed through baseline comparative batch trials. All batch experiments, including biosorbent-free controls, were conducted in triplicate to evaluate their reproducibility. Chitosan exhibited limited uranium removal, with a maximum of 34.68% at 8 μg/L. It also formed viscous suspensions that hindered filtration. In contrast, M. oleifera seeds demonstrated superior adsorption performance, achieving a maximum removal efficiency of 99.32% and a maximum adsorption capacity of 0.93 mg/g (932 µg/g). Analysis of means (ANOM) and analysis of variance (ANOVA) identified initial pH and initial uranium concentration as the co-dominant factors governing removal efficiency. The highest removal efficiency was obtained at 484 µg/L, pH 4, 25 °C, 2.0 g/L adsorbent dosage, and 90 min contact time. Adsorption isotherm modeling derived from dedicated equilibrium trials showed strong agreement with the Freundlich model (R2 > 0.95), consistent with sorption onto energetically heterogeneous surface sites. Overall, unmodified M. oleifera seeds show high baseline efficacy for dilute uranium removal. However, the optimum conditions identified here are more acidic than the near-neutral pH of most NORM-impacted waters; thus, practical implementation must also account for competing carbonate speciation.