The well-accepted assumption of metallic iron (Fe 0 ) acting as electron donor for environmental remediation has created an unstable domain of knowledge for the past 23 years. This assumption is discouraging some outstanding and prospective scientists from correctly interpreting their experimental results. Such a situation is a recipe for long-term decline. The critical situation cannot be solved with simplistic approaches. It is now imperative to develop an understanding to defend the difficulties of this assumption and re-orient Fe 0 mediated remediation research as a whole.

Continuous gravity-fed column experiments using the methylene blue (MB) discoloration method were performed to characterize the suitability of a pozzolan (PZ) specimen as alternative admixing aggregate for metallic iron filters (Fe 0 -filters). Investigated systems were: (i) pure sand, (ii) pure PZ, (iii) pure Fe 0 , (iv) Fe 0 /sand, (v) Fe 0 /PZ, and (vi) Fe 0 /sand/PZ. The volumetric proportion of Fe 0 was 25%. The volumetric proportions of the Fe 0 /sand/PZ system was 25/45/30. The initial MB concentration was 2.0 mg·L −1 , 6.0 g of Fe 0 was used, and the experiments lasted for 46 days. The individual systems were fed with 3.9 to 8.4 L (7.80 to 16.69 mg of MB) and were characterized by the time-dependent changes of: (i) the pH value, (ii) the iron breakthrough, (iii) the MB breakthrough, and (iv) the hydraulic conductivity. Results showed that the Fe 0 /sand/PZ system was the most efficient. This ternary system was also the most permeable and therefore the most sustainable. The suitability of MB as a powerful operative indicator for the characterization of processes in the Fe 0 /H 2 O system was confirmed. The tested PZ is recommended as an alternative material for efficient but sustainable Fe 0 filters.

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The absorption and remediation power of natural coal (NC) and its contribution to the harvesting of corrosion products (CPs) resulting from electrochemical processes of Fe° oxidation in the reactive zone (RZ) of Fe°/