Enhanced Cr(VI) removal by zero-valent iron coupled with weak magnetic field: Role of magnetic gradient force

The influence of magnetic field (MF) flux intensity on the kinetic of Cr(VI) sequestration by zero-valent iron (ZVI) with different particle sizes was investigated to identify the relative contribution of Lorentz force (F-L) and magnetic gradient force (F-Delta B) in the enhancing effect of WMF. The Cr(VI) removal rate enhanced significantly with increasing the MF flux intensity from 0 to 2.0 mT. However, the superimposed MF with flux intensity as high as 10.0 mT induced negligible improvement in Cr(VI) removal by the non-ferromagnetic Zn-0, suggesting the minor role of F-L. The enhancing effect of WMF on Cr(VI) removal improved with decreasing ZVI particle size, which was evidenced by the increase of the ratio of Cr(VI) removal rate constant with MF of 2.0 mT to that without MF (R-WMF) from 1.2 to 11.3 as the iron particle size decreased from 421.2 to 18.1 mu m. There was a strong positive correlation between R-WMF of ZVI samples with different sizes and the maximum product of MF flux intensity times MF gradient of these ZVI samples, suggesting that F-Delta B was the major driving force for the enhancing effect of WMF. The findings of this study will definitely favor optimizing the ZVI/WMF technology for environmental decontamination. (C) 2016 Elsevier B.V. All rights reserved.