Nanoscale zero-valent iron loaded vermiform expanded graphite for the removal of Cr (VI) from aqueous solution

Cr (VI) is indispensable in industrial manufacturing, and its extensive
use leads to severe heavy-metal pollution in the water environment around
people, posing a great danger to physical health and living environment of
multitudinous organisms. Expanded graphite (EG) is considered as a typical
material for adsorption, while nanoscale zero-valent iron (nZVI) can be
applied to degrade and sedimentate various organic or inorganic
pollutants. In this study, a simultaneous collaboration of EG and nZVI is
carried out, with the investigation on the influence of different test
conditions for adsorption performances. These findings demonstrate that
nZVI@EG manifests favorable adsorptive performance on the removal of
hexavalent chromium efficiently. nZVI, acted as an electron donor, is
supposed to reduce Cr(VI) to Cr(III), turning itself into iron oxide or
hydroxide. The whole process is an exothermic reaction, accompanying
chemical reduction and physical adsorption. And Cr(III) is fastened on the
appearance by deposition of chromium hydroxide or ferrochromium complex
precipitation, which greatly reduces the total chromium content in the
aqueous solution. Herein, as a new composite adsorbent, nZVI@EG shows
promising prospects of practical applications in water contamination and
environmental remediation.