Effect of pyrolysis conditions on chemical properties of carbonized rice husks for efficient NH4+ adsorption

Ammonium ions (NH 4 + ) are commonly found in contaminated water and are a contributing factor to water eutrophication. Carbonized rice husk, derived from various biomass sources, possesses a porous structure, and its characteristics are influenced by the feedstock and pyrolysis conditions. Hence, this study aimed to investigate the applicability of carbonized rice husk as an absorbent for NH 4 + removal. The adsorption kinetics were analyzed using the Pseudo-first-order and Pseudo-second-order models, while the adsorption characteristics were assessed using the Langmuir and Freundlich isotherms. The adsorption rate of NH 4 + by carbonized rice husk increased until 240 min and then gradually approached equilibrium state. Notably, the highest NH 4 + adsorption rate was observed in pH 7.1 carbonized rice husk 36.045 mg/g∙min. Moreover, the NH 4 + adsorption capacity exhibited an increase with increasing concentration and quantity of the solution. The pH of the carbonized rice husk was found to influence the NH 4 + adsorption process, with higher pH values corresponding to increased NH 4 + adsorption rates. The NH 4 + sorption rate carbonized rice husk was higher in pH 11.0 at 31.440 mg/g compared to pH 6.1 (7.642 mg/g) and pH 7.1 (10.761 mg/g). These findings highlight the impact of pyrolysis conditions on the adsorption characteristics of carbonized rice husk.