Natural gums-derived hydrogels for adsorptive removal of heavy metals: A review

This review explores advancing and refining hydrogels derived from natural gums for heavy metal ion adsorption, focusing on their efficiency, capacity, and influencing parameters. The high adsorption capacity of these hydrogels, with values reaching up to 384.6 mg/g (Pb²⁺) and 203.7 mg/g (Cu²⁺), is linked to functional moieties like -COOH and -OH, which bind to metal ions through electrostatic interactions, exchange of ions, and coordination mechanisms. Adsorption efficiency is governed by conditions such as duration of contact, temperature, and pH. Temperature studies imply that adsorption occurs through an endothermic mechanism, with positive ΔH values and negative ΔG values, validating the spontaneity and efficiency of the process. Adsorption isotherms, including Langmuir and Freundlich models, have shown promising fits, with a high correlation coefficient (r² > 0.9). The kinetic study reveals that the adsorption follows pseudo-second-order kinetics, implying a chemisorption mechanism. The occurrence of interfering ions (e.g., Na⁺, Ca²⁺) can reduce adsorption efficiency, but their impact is minimal at lower concentrations. Overall, gum-based hydrogels provide an eco-conscious and reliable approach for metal ion removal in aqueous solutions, showing potential for large-scale environmental applications. Further studies focusing on improving adsorption capacity and scalability are recommended to enhance their practical utility in wastewater treatment.