METALLIC IRON FOR WATER TREATMENT: PREVAILING PARADIGM HINDERS PROGRESS

Abstract

The technology of using metallic iron (Fe-0) particles for water treatment is now 20 years old. In it original form, millimetre (mm Fe-0) and micrometer (mu m Fe-0) particles were used. This conventional material has been modified for efficiency improvement. Relevant modifications included: (i) reducing the particle size down to nano-dimensions (nm Fe-0), (ii) alloying Fe-0 with a second/third metallic element to generate bimetallic/trimetallic systems (e.g. Fe-0/Pd-0), (iii) mixing conventional Fe-0 with redox-active components like granular activated carbon, MnO2, Fe3O4, (iv) adding external Fe-II to Fe-0/H2O systems, and (v) using some combinations of tools (i) though (iv) (e.g. Fe-II/Fe3O4/Fe-0, nano Fe-0/Pd-0). Other metallic elements (e.g. Al-0, Mg-0, Zn-0) have also been tested. A critical look behind the mechanism of involved processes in Fe-0/H2O systems reveals that made modifications accelerate iron corrosion, and thus the production of secondary reducing agents (Fe-II, H/H-2). The net result is that the electrochemical Fe corrosion is not necessarily simultaneous to well-documented contaminant reduction. The research community has not yet considered this evidence as Fe-0 is still presented as an environmental reducing agent. The present article clarifies this key issue.