Efficient remediation of Cr(VI)-contaminated water and soil via polyethyleneimine-functionalized magnetic sludge biochar

In this study, a polyethyleneimine (PEI)-modified magnetic sludge biochar (N@FeBC) was prepared via coprecipitation and impregnation methods for treating Cr(VI) contamination in aqueous and soils. Under conditions of pH 3 and 298 K, N@FeBC exhibited a utmost Cr(VI) removal amount of 82.97 mg/g. The removal behaviors were most accurately characterized the pseudo-second-order and Langmuir model. Thermodynamics analysis revealed that the reactions were spontaneous, endothermic, and accompanied by increased system entropy. The removal capacities progressively decreased as the pH rose from 2 to 10, with the optimal removal amounts occurring under acidic conditions. While coexisting cations had negligible effects on Cr(VI) adsorption, anions inhibited the process to varying degrees. Interestingly, humic acid presence improved the efficiencies of Cr(VI) removal. Notably, N@FeBC reduced low-concentrations of Cr(VI) in various water matrices to below the WHO drinking water standard (0.05 mg/L), and retained excellent performance after 15 reuse cycles. In soil stabilization tests, N@FeBC more effectively reduced Cr(VI) toxicity in contaminated soil. Mechanistic investigations revealed that Cr(VI) removal occurred via electrostatic attraction to protonated surface functionalities, partial reduction to Cr(III), and subsequent coordination with functional groups. This study indicates that N@FeBC can serve as an efficient material for removing Cr(VI) contamination.