Formation and mechanism of nanoscale zerovalent iron supported by phosphoric acid modified biochar for highly efficient removal of Cr(VI)

The effect of phosphoric acid modified biochar on activity of nanoscale zero valent iron particles is not clear until now. In this research, Egeria najas powder driven biochar-supported nanoscale zero valent iron was modified by phosphoric acid (P-BC/nZVI) for highly effective removal of Cr(VI) from wastewater. The TEM and XRD of P-BC/nZVI indicated that nZVI particles were successfully immobilized on the P-BC surface. The batch experiment results show that the Cr(VI) removal efficiency by P-BC/nZVI was higher than that of BC/nZVI, nZVI, P-BC and BC. Moreover, the optimal ratio of nZVI to P-BC lies at 3:1 with fixed P-BC/nZVI dosage of 0.75 g/L, initial Cr(VI) concentration of 20 mg/L, solution pH of 2, and reaction temperature of 333 K. Additionally, Cr(VI) removal capacities by nZVI, BC/nZVI and P-BC/nZVI aged for 15 days in water were 12.9 %, 28.55 % and 99.35 %, respectively. Furthermore, corresponding reaction kinetics fitted well with pseudo-second order model, and adsorption isotherm fitted to Sips isothermal model. The SEM-EDS and XPS confirm that Cr(VI) was participated in the reaction, and about 63.43 % of Cr(VI) was reduced to Cr(III), and the rest was adsorbed on the surface of P-BC/nZVI. The removal mechanism of Cr(VI) by P-BC/nZVI was complex, including adsorption, reduction and surface complex formation.