Palm kernel shell activated carbon: circular zinc chloride activation and batch adsorption of methylene blue

Abstract This study was aimed to investigate the effectiveness of recycled activator solutions to produce activated carbons. The activated carbons were evaluated for physicochemical characteristics and methylene blue adsorption. Activated carbon with fresh ZnCl 2 solution and palm kernel shell char were prepared for comparison. The fresh activated carbon (AC1) exhibits higher surface area (891 m 2 /g), followed by the ones produced using the recycled activator solutions from the first (AC2, 681 m 2 /g) and second (AC3, 602 m 2 /g) activations. The former exhibits a higher methylene blue capacity of 379 mg/g. Although AC3 exhibits a lower adsorption capacity (204 mg/g), it shows a slightly higher Langmuir b constant, indicating stronger adsorbate–adsorbent interactions at individual sites. The performance of recycled-activator carbons positions them among advanced composite adsorbents recently reported for efficient cationic pollutant removal with excellent recyclability, demonstrating that activator recycling does not compromise functional performance. The equilibrium and kinetics data obeyed the Redlich–Peterson and pseudo-second-order models, respectively, while the thermodynamic parameters suggest that the process is endothermic, feasible and spontaneous. Water is more effective to regenerate the spent activated carbon with desorption efficiency of 98.3 %. To conclude, the use of recycled activator solutions is viable to produce activated carbons with considerable performance for dye wastewater treatment.