Structure and properties of nanoscale zero-valent iron supported on multimorphologies kaolinite and its enhanced removal of Cr(VI) from water

Abstract

Kaolinite has various morphologies, stable chemical properties, and abundant reserves. To broaden its application in the environment, kaolinite-based nano zero-valent iron composite (nZVI/Kaol) was synthesized for the removal of hexavalent chromium (Cr(VI)) in water. The results showed that the removal rate of Cr(VI) by nZVI/Kaol (the Fe/Kaol mass ratio was 30%) reached 91.7% after 60 min reaction in Cr(VI) solution with an initial concentration of 20 mg/L (pH=7), while the removal efficiencies of Cr(VI) by nZVI and kaolinite were 34.5% and 5.6%. The characterization showed the different morphologies of kaolinite led to nZVI particles with uneven sizes loaded on the surface, that the size of nZVI loaded on rodlike kaolinite (50–100 nm) tended to be smaller than flaky kaolinite (150–200 nm), so the utilization of various sizes of nZVI enhanced Cr(VI) removal. The removal process matched the pseudo-second-order kinetic model and Langmuir isothermal adsorption model better. The results of thermodynamic calculation verified the removal of Cr(VI) by nZVI/Kaol to be endothermic. FTIR and XPS analysis showed that the removal mechanism of Cr(VI) by nZVI/Kaol included adsorption, redox and co-precipitation.