Mn(II) ion adsorption using κ-carrageenan beads as a bio-based adsorbent

Carrageenan, an anionic polysaccharide commercially extracted from red algae, possesses ester sulphate functional groups, endowing it with significant potential as an adsorbent for heavy metal cations. This study investigates the efficacy of κ-carrageenan beads for the removal of manganese(II) ions from contaminated aqueous solutions, addressing the environmental concerns associated with elevated Mn(II) concentrations. κ-carrageenan beads were successfully synthesized from commercially available powder, and their adsorption capabilities were confirmed through Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Adsorption parameters were systematically optimized, revealing optimal conditions at pH 3, a contact time of 120 minutes, and an adsorbent dosage of 0.1 g/100 mL. Kinetic study demonstrated that the adsorption process followed pseudo-second-order kinetics, while equilibrium data conformed to the Langmuir adsorption isotherm model, indicating monolayer adsorption. Furthermore, thermodynamic studies revealed that the adsorption of Mn(II) onto κ-carrageenan beads was an endothermic and spontaneous process. These findings can serve as a valuable reference for further applications of this material as a relatively low-cost, easy-to-prepare, yet effective bio-based adsorbent in reducing Mn(II) pollution levels in open waters.