Heavy metal removal by hydrogel synthesized from rice bran/acrylic acid/sodium alginate

This study reports the synthesis of a novel hydrogel adsorbent prepared from rice bran (RB), acrylic acid (AA), and sodium alginate (SA) for the removal of Cu²⁺ and Ni²⁺ from aqueous solutions. RB, an abundant agricultural by-product rich in cellulose and functional groups, was combined with SA and polymerized with AA to produce a cost-effective, eco-friendly, and reusable adsorbent. Adsorption performance was systematically evaluated under varying pH values, temperatures, metal ion concentrations, and adsorbent dosages. The optimum conditions for Cu²⁺ removal were pH 5.5, 30 °C, and an adsorbent dosage of 1 pcs, yielding a maximum adsorption capacity of 26.5 mg g⁻¹ with 88% removal efficiency. For Ni²⁺, the best performance was achieved at pH 8 and 30 °C, with a capacity of 41.81 mg g⁻¹ and 62% removal efficiency. Isotherm analysis showed that adsorption followed the Langmuir model, while kinetics were best described by the pseudo-second-order model. The adsorbent retained over 85% of its initial capacity after five adsorption-desorption cycles, confirming good reusability.