Potential of modified iron-rich foundry waste for environmental applications: Fenton reaction and Cr(VI) reduction

A magnetic fraction (15%) from a waste of foundry sand (WFS), composed of sand, carbon, bentonite clay and iron (10%) was modified by thermal treatment at 400, 600 and 800 degrees C under inert atmosphere. Mossbauer analyses showed that the thermal treatment increased the amount of Fe3O4 from 25 to 55% by reduction of Fe2O3 and highly dispersed Fe3+ by the carbon present in the waste. The Fe3O4 caused a significant increase on the activity of two important reactions with application in environmental remediation: the Fenton oxidation of indigo carmine dye with H2O2 and the reduction of Cr(VI) to Cr(III). The magnetic fraction of WFS was also mixed with hematite (Fe2O3) and thermally treated at 400, 600 and 800 degrees C. This treatment produced large amounts of surface Fe3O4 and increased substantially the rate of Fenton reaction as well as Cr(VI) reduction. This reactivity combined with the presence of carbon (an adsorbent for organic contaminants), bentonite clay (an adsorbent for metallic contaminants) and the granulometry/packing/hydrodynamic features make WFS a promising material for use in reactive permeable barriers. (C) 2011 Elsevier B.V. All rights reserved.