Effect of Sand Co-Presence on CrVI Removal in Fe0-H2O System

The aim of the present study was to provide new knowledge regarding the effect of non-expansive inert material addition on anionic pollutant removal efficiency in Fe-0-H2O system. Non-disturbed batch experiments and continuous-flow-through column tests were conducted using Cr-VI as a redox-active contaminant in three different systems: "Fe-0 + sand", "Fe-0 only" and "sand only". Both experimental procedures have the advantage that formation of (hydr)oxide layers on Fe-0 is not altered, which makes them appropriate proxies for real Fe-0-based filter technologies. Batch experiments carried out at pH 6.5 showed a slight improvement of Cr-VI removal in a 20% Fe-0 system, compared to 50, 80 and 100% Fe-0 systems. Column tests conducted at pH 6.5 supported results of batch experiments, revealing highest Cr-VI removal efficiencies for "Fe-0 + sand" systems with lowest Fe-0 ratio. However, the positive effect of sand co-presence decreases with increasing pH from 6.5 to 7.1. Scanning electron microscopy-energy dispersive angle X-ray spectrometry and X-ray diffraction spectroscopy employed for the characterization of Fe-0 before and after experiments indicated that the higher the volumetric ratio of sand in "Fe-0 + sand" system, the more intense the corrosion processes affecting the Fe-0 grains. Results presented herein indicate the capacity of sand at sustaining the efficiency of Cr-VI removal in Fe-0-H2O system. The outcomes of the present study suggest that a volumetric ratio Fe-0:sand = 1:3 could assure not only the long-term permeability of Fe-0-based filters, but also enhanced removal efficiency of Cr-VI from contaminated water.