Removal of Aqueous Cr(VI) by Tea Stalk Biochar Supported Nanoscale Zero-Valent Iron: Performance and Mechanism

Biochar-supported nanoscale zero-valent iron (800nZVI/BC) was prepared by carbothermal synthesis to remedy Cr(VI) wastewater. More than 99% of Cr(VI) was efficiently removed within 30 min at pH 2, and the maximum adsorption amount of Cr(VI) by 800nZVI/BC was 48.45 mg/L. The structural characteristics of 800nZVI/BC composite were determined adopting SEM, XRD, FTIR, and XPS. Batch experiments exhibited the Cr(VI) removal processes followed the pseud-second-order kinetics and Langmuir's adsorption model. The effects of Fe/C mass ratio, 800nZVI/BC dosage, Cr(VI) concentration, initial pH, and different water bodies on Cr(VI) removal were investigated. The composites still showed a relatively stable Cr(VI) removal ability in oxidation resistance tests. The retention rates of Cr(VI) removal efficiency were respectively higher than 85% and 65% after 21 days aging in air and simulated groundwater. The Cr(VI) removal mechanism was studied according to the performance and structural characteristics. The removal of Cr(VI) might be relevant to the reduction of Cr(VI) by Fe-0, Fe2+, and FeO, C-OH on the 800nZVI/BC surface and the formation of complex.