Enhanced hexavalent chromium removal performance and stabilization by magnetic iron nanoparticles assisted biochar in aqueous solution: Mechanisms and application potential.

The superiority of the nanoscale zero valent iron (nZVI) assisted biochar (BC) composites compared to traditional nZVI and its application feasibility are still unclear. This study aimed to provide valuable information for practical application. Firstly, the Fe/BC mass ratio of 2:1 during the preparation of nZVI-BC was proved obtaining the complete Cr removal. Then, results revealed that the initial pH value tuned Cr removal performance via varying existing Cr species, surface charge, and chemical states of iron nanoparticles (NPs). Improvement of colloidal stabilization and positive surface charge attributed to enhancement of Cr removal of nZVI-BC. The Cr removal process was well described using pseudo-second-order kinetic. By Langmuir isotherm model, the maximum removal capacity (58.82 mg g) was determined. Moreover, the multiple evidences (XRD, XPS, FTIR, and TEM results) explained the mechanisms of Cr removal (i.e. electrostatic force, complexes, metal reduction, and precipitates on the edges). Little inhibitory effect of coexisting anions (SO, PO, and NO) and well regeneration ability (82.2% removal efficiency after five cycles using acid washing), along with well Cr removal efficiencies of real contaminated water (electroplating wastewater, tannery wastewater and groundwater) treatment, suggested nZVI-BC was considered as a superior and cost-effective choice for Cr included polluted water treatment.