Removal of Mn(II) ion from aqueous solution onto cassava stem-derived activated carbon: Adsorption isotherms and kinetics studies

The high cost of commercial activated carbon due to its high production expenses, has driven increasing demand in lignocellulosic biomass-derived activated carbon as low-cost adsorbent for adsorbing emerging contaminants from drinking and wastewater due to its high surface area and high adsorption capacity. In this study, the mechanism of equilibrium adsorption and kinetics of Mn(II) ion in drinking and wastewater onto cassava stem-crude potash derived activated carbon were studied. The cassava stem was carbonized at 818.68 ⁰ C for 1.45 h at impregnation ratio of 2:1. The chemically activated cassava stem charcoal was characterized for pH of 7.01 ± 0.10, moisture content of 4.09 ± 0.29%, volatile matter of 23.66 ± 0.20%, ash content of 3.13 ± 0.12%, fixed carbon content of 69.12 ± 0.09%, bulk density of 0.40 ± 0.11 g/mL, iodine number of 1080.75 ± 0.21 mg/g, surface area of 1101 ± 0.20 m ² /g and attrition value of 62 ± 0.12%. Data from equilibrium adsorption were analyzed with two model equations which were Langmuir and Freundlich models. The Langmuir (R ²  = 0.9931) model correlated the experimental data better than the Freundlich (R ²  = 0.9881) isotherm model. The maximum adsorption capacity (q _m ), intensity of adsorption (K _L ) and separation factor (R _L ) were obtained from Langmuir plot. Data from adsorption kinetics were analyzed with pseudo-first-order and pseudo-second-order models. The results showed that the pseudo-second-order (R ²  = 0.9997) was a better model, describing the adsorption kinetics data compared to the pseudo-first-order model (R = 0.9789). The maximum monolayer adsorption capacity of the activated carbon was evaluated as 555.56 mg/g.