Pathways for Contaminant Reduction
Zero valent iron is capable of reducing chlorinated compounds to harmless components, as shown in the general reaction formula below:
2Fe0 + R-Cl + 3H2O → 2Fe2+ + R-H + 3OH– + H2 + Cl– (R = Aryl group)
The chlorinated compounds can be reduced as follows:
1. Reduction at the metal surface in the presence of a proton donor
Fe0 + R-Cl + H+ → Fe2+ + R-H+ Cl– (1)
2. Continuation of reaction 1 by the further oxidation of Fe2+ to Fe3+
2Fe2+ + R-Cl + H+→ 2Fe3+ + R-H+ Cl– (2)
3. The hydrogen gas which is produced in the corrosion reaction of water with zero-valent iron can also be involved in the dechlorination of VOCs.
Fe0 + 2H2O → Fe2+ + H2 + 2OH– (3)
H2 + R-Cl → R-H + H+ + Cl– (4)
In the estimate of the amount of zero valent iron needed, the reaction of zero valent iron with dissolved oxygen (5), water (3) and other oxidized organic and inorganic components (e.g. nitrate, sulfate) must also be taken into account.
2Fe0 + 4H+ + O2 → 2Fe2+ + 2H2O (5)