Adsorption of manganese(Ii) ion in the water phase by citric acid activated carbon of rice husk

Abstract

Purpose - In this study, the possibility of the application of rice husks for adsorbing Mn(II) ion in the water phase has been studied. Design/Methodology/Approach - Experimental studies have been initiated by preparing activated carbon from rice husks. The activation of rice husks was done using both physical and chemical treatment methods through heating at 110 °C and washing with citric acid activator at 0.2 M, 0.4 M, and 0.6 M. The adsorption tests were conducted as two part tests: Preliminary and primary. The preliminary test was conducted to choose the best condition of four independent variables, i.e., contact time (0-120 minutes), activator concentrations (0.2, 0.4, and 0.6 M), initial Mn(II) concentrations (10, 20, 50, 100, 200, and 400 mg/L), and adsorption temperatures (30, 47, and 67 °C). Findings - By identifying the substituted groups using Fourier Transform Infrared Spectroscopy after activation with citric acid, it was found that the highest transmittance percentage was present in activated carbon with 0.2 M of citric acid. The best adsorption capacity and efficiency was 13.87 mg/g and 79.60%, respectively, which were obtained at 200 mg/L initial concentration with a 0.2 M citric acid concentration for 120 min contact time at 47 °C. These results lead to a conclusion that rice husks after activation with citric acid can be applied as an adsorbent for Mn(II) adsorption in the water phase. Research Limitations/Implications - The activated carbon produced was only applicable for the adsorption of Mn(II) ions from the water phase, but not applicable for the adsorption of other heavy metals ions. Practical Implications - Rice husks were potentially prepared as an adsorbent for Mn(II) ion adsorption in the water phase that was low cost, environmental friendly, and easy to prepare. Originality/Value - Activated carbon prepared from biomass was mostly carried out using acids at high concentrations while the study was conducted using weak acids (citric acid) at low concentrations.