Removal of Cr(VI) from aqueous solution by Rice-husk-based activated carbon prepared by Dual-mode heating method

Rice husk-based activated carbon was prepared with the help of zinc chloride using microwave and electrical dual-mode heating. The pore characteristics and chemical properties of rice husk-based activated carbon (RH-AC) were characterized by BET, XRD, Raman spectra, FTIR and pH_IEP (pH of isoelectric point). The specific surface area of RH-AC is 1719.32 m²/g with a total pore volume of 1.05 cm³/g. The performance of RH-AC for removing Cr(VI) from aqueous solution was examined considering the variation of the contact time (0–120 min), pH value (2.0–9.0), adsorbent dose (0.5–3.0 g/L), initial concentration (28–145 mg/L) and solvent temperature (15–45 °C). The ideal pH for Cr(VI) removal is between 2.0 and 3.0 with the equilibrium time of 90 min, achieving the maximum adsorption capacity of 56.82 mg/g with the pH of 3.0. Comparable study on the established kinetic models and isotherms to simulate the removal of Cr(VI) by RH-AC was carried out to sort out the inherent mechanism of the absorption. Reasonable agreements could be obtained by the pseudo-second-order kinetic model and Langmuir, Freundlich and Tempkin isothermal models. Results from Body model simulation suggest that external mass transfer was the essential cause for rate-controlling in the adsorption process of Cr(VI).