Facile Improvement of Nanoscale Zero-Valent Iron Activity with Exceptional Stability for Reduction of Cr(VI)

In the present study, a highly active reaction system of nanoscale zero-valent (nZVI) was successfully established by enhancing nZVI with a biodegradable complexing agent (CA) and applied to hexavalent chromium [Cr(VI)] removal. Both iminodisuccinic acid (IDS) and N,N-bis(carboxymethyl)glutamic (GLDA) are good biodegradable CAs with strong ability to Cr(III)/Fe(II)/Fe(III). Cr(VI) (10.0 mg L-1) removal efficiency by nZVI increased from 60.1% to 100.0% with the addition of 4.0 mmol L-1 IDS or GLDA for 60 min. A characterization analysis suggested that nZVI and CA enhanced Cr(VI) removal by decreasing the surface passivation layer, which was expected to be (CrxFe1-x)(OH)3. In addition, the Cr(VI) removal efficiency decreased with increasing initial pH, and appropriate CA dosage (4.0 mmol L-1) and temperature (25.0 degrees C) were beneficial for the efficient reduction of Cr(VI). An amount of 94.8% of Cr(VI) removal was achieved within the initial 2 min when the experiment conditions were as follows: 0.1 g L-1 nZVI, 4.0 mmol L-1 GLDA, the temperature at 25.0 degrees C, an initial pH of 7.0, and stirring at 200 r min-1. And the Cr(VI) removal by GLDA improved nZVI maintained above 84.3% after three consecutive cycles. The results indicate CA-enhanced-nZVI could be a promising approach for the Cr(VI) removal in a solution.