Effects of physicochemical factors on Cr(VI) removal from leachate by zero-valent iron and α-Fe₂O₃ nanoparticles

The effects of nanoparticle dosage, initial hexavalent chromium concentration, pH value, reaction temperature, and initial concentration of humic acid (HA) on chromate (CrO₄²⁻) removal from landfill leachate by nanoscale zero-valent iron (NZVI) and hematite (α-Fe₂O₃) nanoparticles were examined in the present investigations. The Cr(VI) removal rate decreased as the initial Cr(VI) concentration and the reaction temperature increased, whereas corresponding removal rate by NZVI was higher than that of α-Fe₂O₃. The optimum pH for the removal of Cr(VI) by NZVI was found to be 5.0 and more than 99.0% of Cr(VI) was removed within 5 h. However, the removal rate by α-Fe₂O₃ decreased as pH increased. Presence of HA resulted in substantial reduction in the rate and extent of Cr(VI) removal by NZVI, whereas Cr(VI) removal rate by α-Fe₂O₃ did not significantly decrease as HA concentration increased from 0.5 g/L to 3.0 g/L. Increasing the dosage of nanoparticles enhanced the rate constant and the removal of Cr(VI) by NZVI and α-Fe₂O₃ followed pseudo-first-order reaction kinetics. The information should be very useful for the successful application of NZVI and α-Fe₂O₃ for the treatment of groundwater or raw wastewater.