A new sorbent was designed by functionalization of a bio-based composite made of chitosan and Arabic gum. The grafting of two sulfonate-bearing moieties allows reaching, at the optimum pH (i.e., pH0 4), a sorption capacity as high as 1.48 mmol U g−1 (with strong affinity; bL being close to 356 L mmol−1). The Sips equation fits better sorption isotherms than the Langmuir equation. The maximum sorption capacity increases with temperature (while the affinity coefficient does not follow a continuous trend). The sorption kinetics are very fast; 20 min of contact are sufficient for reaching the equilibrium and the kinetic profiles are successfully fitted by the pseudo-first order rate equation. HCl solutions (0.2 M) are highly efficient for completely desorbing bound uranyl ions; the loss in sorption efficiency does not exceed 3% after 5 re-use cycles. At pH above 4, the sorbent shows high selectivity against Ca(II), Mg(II), Al(III) and Zn(II) (against Fe(III) and Cu(II), to a lesser extent). The sorbent is successfully tested for the decontamination of water samples collected from five wells located in Sinai (Egypt): uranium removal approaches 100%; metal ions like Cu(II), Fe(III), Zn(II) and Pb(II) are also remarkably recovered from samples at pH0 5.5. Complementary tests (using agar well diffusion method) show that the sorbent brings an additional antimicrobial activity against S. aureus, B. subtilis, E. coli, P. aeruginosa, and C. albicans, with MIC values ranging between 50 and 25 µg mL−1. The sorbent is characterized by negligible toxicity, using the MTT assay method against two normal cell lines (i.e., Vero and HFB4), and a cancerous cell line (i.e., Caco-2).