Role of pre-corrosion of Fe0 on its efficiency in remediation systems: An electrochemical study.

The duration of in-situ generation of iron corrosion products (FeCPs) prior the remediation process (so called "aging" of metallic iron (Fe0)), was found as the key parameter affecting the efficiency of Fe0 for water remediation. Batch experiments were performed in buffered solutions (pH 4.0, 4.7 and 5.5) and under oxic conditions (presence of dissolved oxygen) using Zn2+ as probe contaminant. The time-dependent (0-16 d) concentration changes of aqueous Fe2+ and Zn2+ were monitored using differential pulse polarography (DPP). During the time of pre-corrosion varying from 0 to 6 d, an "induction period" of the corrosion occurs in the first one - 2 h when no Fe2+ ion is released in the solution. After this period, Fe2+ was identified in solution and its concentration progressively increases up to 6 h, then starts to decrease and after 6 d nearly disappears. Experiments with Zn2+ reveal that the most efficient Fe0 remediation occurs after 6 h of pre-corrosion. This coherence thus proves that the presence, the amount and the age of FeCPs ("degree" of corrosion) significantly impact the removal efficiency of Zn2+ in Fe0/H2O systems. The present study severely refute the wording 'reactivity loss' and states that progress in designing sustainable Fe0/H2O systems will not be achieved before the role of "active" FeCPs is clarified.