Synthesis, characterization and kinetics of bentonite supported nZVI for the removal of Cr(VI) from aqueous solution

Bentonite supported nanoscale zero-valent iron (B-nZVI) was synthesized by the sodium borohydride reduction method, characterized with SEM, and used for aqueous Cr(VI) removal. Bentonite decreased nano-Fe0 aggregation and thus increase Cr(VI) removal efficiency. At 35 °C and 250 r min−1, 99% Cr(VI) removal was achieved from aqueous solution containing 50 mg L−1 of Cr(VI) by B-nZVI, while only 66% removal was achieved with unsupported nZVI after an experimental duration of 3 h when the Fe0 loadings were 1.5 g L−1. XRD indicated the existence of iron oxide and iron-chromium hydroxide coprecipitation on the surface of B-nZVI after exposure to an aqueous solution of Cr(VI). Kinetics studies under a series of different conditions showed that reduction of Cr(VI) to Cr(III) could be expressed by pseudo first-order reaction kinetics, with initial Cr(VI) and B-nZVI concentrations, pH and temperature as variables. The apparent activation energy of Cr(VI) remediation by B-nZVI was 21 kJ mol−1, which was characteristic of a chemically controlled reaction. These results demonstrated that B-nZVI could potentially be used as a new material for use in situ remediation.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Bentonite supported nanoscale zero-valent iron (B-nZVI) for the removal of Cr(VI). ► More than 99% Cr(VI) from solution was removed by K-nZVI. ► Characterizations of B-nZVI were by SEM and XRD. ► The formation of a hydroxylated Cr(OH)3 and coprecipitation of CrxFe1−x(OH)3.