Design, preparation, and performance of different adsorbents based on carboxymethyl chitosan/sodium alginate hydrogel beads for selective adsorption of Cadmium (II) and Chromium (III) metal ions.

Developing cost-effective and efficient adsorbents for heavy metals in multicomponent systems is a challenge that needs to be resolved to meet the challenges of wastewater treatment technology. Two adsorbents were synthesized, characterized, and investigated for the removal of Cd and Cr as model heavy metals in their single and binary solutions. The first adsorbent (ACZ) was a nanocomposite formed of O-Carboxymethyl chitosan, sodium alginate, and zeolite. While, the other (ACL) contained ZnFe layered double hydroxides instead of the zeolite phase. Adsorbents were characterized using XRD, FTIR, SEM, and swelling degree analysis. For single heavy metal adsorption isotherms, data for both adsorbents was best fitted and indicated a multilayer adsorption nature. For binary adsorption, Langmuir model with interacting parameters showed the best results compared to other models for both pollutants. For single system, Avrami model was found to be the best model representing the adsorption kinetics data, which indicates that the mechanism of adsorption follows multiple kinetic orders that may change during duration of adsorption process. Numerous interaction mechanisms can occur between the heavy metals and functional groups in the synthesized hydrogels such as NH, COOH, and OH groups leading to efficient adsorption of metal ions.