Calcium alginate–bentonite–activated carbon composite beads as highly effective adsorbent for methylene blue

• An activated carbon–bentonite–alginate (ABA) composite was synthesized facilely.
• ABA showed a prominent existence of exchangeable cations.
• ABA was proven to be an extraordinary adsorbent for the removal of model dye methylene blue.
• The regenerated ABA was successfully employed several times for the adsorption.

Three adsorbents, namely, bentonite–alginate beads, activated carbon–alginate beads, and activated carbon–bentonite–alginate beads (ABA) were prepared for the adsorption of methylene blue (MB). The effects of solution pH (3–11), temperature (30, 40, and 50 °C), initial concentration (25–500 mg/L), and contact time were investigated. Results showed that the maximum monolayer adsorption capacity of ABA beads for the adsorption of MB was 756.97 mg/g at 30 °C. Furthermore, the adsorption kinetics illustrated the suitability of employing the pseudo-second-order kinetic model. The equilibrium adsorption data fitted the Freundlich isotherm well. In addition, the ABA composite exhibited more than 70% adsorption uptake capacity after six regeneration cycles. The outcomes of this study suggest the potential of ABA composite for cationic dye removal.