In this study, a novel magnetic adsorbent based on cellulose/Fe3O4/SiO2, modified with bis(acetylacetone)ethylenediimine, was synthesized and utilized for the effective removal of Co(II) ions from aqueous solutions. Equilibrium concentrations of Co(II) ions in solution was set by using 2,2′,2′′,2′′′-{(1,1-dioxo-2,1λ6-benzoxathiole-3,3(1H)-diyl)bis[(6-hydroxy-5-methyl-3,1-phenylene)methylenenitrilo]} tetraacetic acid (xylenol-orange) (R) as reagent. Various factors influencing the adsorption process were examined, including the effects of pH, contact time, ionic strength, and the initial concentration of metal ions. The sorption of cobalt (II) ions with the synthesized magnetic sorbent under static and dynamic conditions was studied. Optimal adsorption performance was achieved at a pH of 8. It was determined that 0.5 M HCl solution achieves the most effective desorption of Co(II) ions from the sorbent, with a desorption efficiency of 97%. The proposed method was employed for the detection of trace levels of cobalt (II) in water samples collected from the Caspian Sea.