Adsorption properties and mechanism of Cr(VI) by Fe2(SO4)3 modified biochar derived from Egeria najas

Abstract

The aquatic plant Egeria najas based biochar was innovatively constructed by modifying it with Fe2(SO4)3 (Fe2(SO4)3 @EN-BC) for Cr(VI) removal. The characterizations of Fe2(SO4)3 @EN-BC confirmed that Fe2(SO4)3 was attached to biochar in form of Fe2O3 after hydrolysis and calcination under high temperature. The results showed that Fe2(SO4)3 @EN-BC had a high removal efficiency of Cr(VI) with approaching 99.88%, which was about 7 times higher compared to unmodified biochar (EN-BC). Batch experiments of Cr(VI) removal included initial concentration, reaction temperature, solution pH and kinetics were conducted. The adsorption kinetics could be more accurately explained using pseudo-second order kinetics model, indicating the chemical adsorption controlled the reaction process. According to the Langmuir model, the maximum adsorption capacities for Cr(VI) were 138.79, 159.36 and 190.91 mg/g at 298, 313 and 333 K, respectively. Moreover, based on FTIR and XPS results, the Fe2(SO4)3 @EN-BC surface was loaded with many functional groups conducive to Cr(VI) adsorption. The main removal mechanisms of Cr(VI) by Fe2(SO4)3 @EN-BC included adsorption and reduction, and the percentage of Cr(VI) removed by adsorption and reduction were 19.1% and 80.9%, respectively.