Cationic and anionic dyes removal by low-cost hybrid alginate/natural bentonite composite beads: Adsorption and...

Using the extrusion method, novel hybrid beads were prepared from natural bentonite and alginate. Alginate to clay ratios was varied (1/1; 1/2 and 1/3) and used to eliminate two dyes (methylene blue and Congo red).Adsorbents were characterized by Fourier transformed infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller method (BET) from N₂ adsorption-desorption isotherm at 77 K, and the point of zero charge (pH_PZC). The adsorption of methylene blue and Congo red was studied according to different parameters. The results showed that isotherms were well described by the Langmuir model justifying monolayer and homogeneous adsorption. Kinetics were well followed the pseudo-second-order model. Adsorption capacities of MB onto A-B 1/1 and CR onto A-B 1/3 were 1171 and 95.55 mg/g respectively. MB adsorption on A-B 1/1 and CR adsorption on A-B 1/3 were endothermic and exothermic respectively. Regeneration study showed that dyes were successfully desorbed from A-B 1/1 and A-B 1/3 with removal percentages of 99.65% and 86.2% respectively in the first cycle. Hybrid alginate-bentonite composites are low-cost, effective and regenerable for a wide variety of dyes.