Sugarcane bagasse-derived biochar for ammonium removal from aqueous solutions: Kinetics, isotherms, and characterization

This study evaluates the performance of biochar derived from sugarcane bagasse as a low-cost adsorbent for ammonium (NH 4 + ) removal from aqueous solutions. Biochar was synthesized at three pyrolysis temperatures (400, 500, and 600 °C), and the sample prepared at 500 °C, with the highest specific surface area of 54.71 m 2 /g, was selected for further investigation. The effect of contact time (0–24 h), initial NH 4 + concentration (50, 75, 100, and 125 mg/L), adsorbent dosage (3, 5, 7, 9, and 11 g/L), and pH (4, 6, 8, 10) on adsorption performance was systematically examined. The highest adsorption amount of 4.0 mg/g was achieved at pH = 10, initial concentration of 50 mg/L, adsorbent dosage of 5 g/L, and equilibrium time of 12 h. The removal efficiency increased from 28% to 35% with increasing adsorbent dosage from 3 to 7 g/L, beyond which no significant improvement was observed. Among the kinetic models tested, the pseudo-second-order model provided the best fit to the experimental data, suggesting that chemisorption may play a significant role in the rate-controlling step. Among the isotherm models, the Langmuir model exhibited the best fit, with a maximum monolayer adsorption capacity of 7.98 mg/g. Microstructure imaging revealed a highly porous structure with surface coverage by ammonium species after adsorption, while X-ray elemental analysis confirmed an increase in surface nitrogen content from 3.3 wt% to approximately 4.4 wt%, verifying successful ammonium uptake. Regeneration tests showed that the biochar retained 82–85% of its initial performance after two cycles. These results demonstrate that sugarcane bagasse-derived biochar is a promising adsorbent for ammonium removal, showing potential as a low-cost adsorbent under the tested batch conditions.