Effect of pH, temperature and co-existing anions on the Removal of Cr(VI) in groundwater by green synthesized nZVI/Ni.

Nanoscale zero-valent iron/nickel (GT-nZVI/Ni) was prepared by green synthesis technology using green tea extracts in this study. The obtained material was characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and BET analyses. Batch experiments were carried out to investigate the effect of pH, initial concentration of Cr(VI), temperature and co-existing anions(CO32-, HCO3-, SO42- and NO3-) on the removal efficiency of Cr(VI) in groundwater. Results showed that 100% Cr(VI) was removed from the aqueous solution containing 5 mg L-1 of Cr(VI) in 30 min when pH value was 5 and reaction temperature was 303 K. Temperature and pH value had a significant effect of reduction rate of Cr(VI). The presence of co-existing anions (CO32-, HCO3-, SO42- and NO3-) inhibited the removal of Cr(VI) by GT-nZVI/Ni and the most significant one was CO32-, the removal efficiency of Cr(VI) decreased to 52.9% when the concentration of CO32- was 10 mmol L-1. The adsorption behavior of Cr(VI) fitted better with Langmuir-Hinshelwood first order reaction kinetic model. Thermodynamic studies indicated the process was spontaneous and endothermic(ΔG°<0, ΔS°>0, ΔH°>0). Therefore, this study provides a reference for further research of GT-nZVI/Ni and practical application of GT-nZVI/Ni in groundwater treatment.