Sustainable magnetic cellulose–alginate beads for selective biosorption of Cd (II) and Ni(II) ions from contaminated waters

This study reports the green synthesis and characterization of magnetic cellulose/alginate/magnetite (CEL/ALG/MAG) composites for the efficient removal of cadmium (Cd (II)) and nickel (Ni (II)) from aqueous solutions. The composites were prepared via an eco-friendly aqueous route and thoroughly characterized using Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) techniques. Structural analysis confirmed successful magnetite (Fe₃O₄) formation (8.1 nm crystallite size) and revealed Fe²⁺/Fe³⁺ mediated crosslinking between components, which reduced cellulose crystallinity and created rough, cavity-rich surfaces despite low specific surface area (0.25-0.28 m² g-1). Batch adsorption experiments demonstrated exceptional removal efficiencies of ≥ 94.8% for Cd (II) and up to 94.4% for Ni (II) at optimal pH 6. Kinetic and isotherm studies indicated a chemisorption-dominated process, well-described by pseudo-second-order and Freundlich models (E > 8 kJ/mol). In competitive systems, the composites showed preferential Cd(II) adsorption (92.9% vs. 65% for Ni (II)), attributed to its favorable ionic characteristics, while magnetite incorporation enhanced Ni (II) uptake through synergistic effects. These sustainable, magnetically recoverable biosorbents combine the advantages of renewable biopolymers with facile magnetic separation, offering a promising solution for industrial wastewater treatment. The findings provide fundamental insights into heavy metal adsorption mechanisms on magnetic biopolymer composites and highlight their potential for practical environmental applications.