Tracing the Scientific History of Fe0-Based Environmental Remediation Prior to the Advent of Permeable Reactive Barriers

Abstract

The technology of using metallic iron (Fe0) for in situ generation of iron oxides for water treatment is a very old one. The Fe0 remediation technology has been re-discovered in the framework of groundwater remediation using permeable reactive barriers (PRBs). Despite its simplicity, the improvement of Fe0 PRBs is fraught with difficulties regarding their operating modes. The literature dealing with Fe0 remediation contains ambiguities regarding its invention and its development. The present paper examines the sequence of contributions prior to the advent of Fe0 PRBs in order to clarify the seemingly complex picture. To achieve this, the current paper addresses the following questions: (i) What were the motivations of various authors in developing their respective innovations over the years?, (ii) what are the ancient achievements which can accelerate progress in knowledge for the development of Fe0 PRBs?, and (iii) was Fe0 really used for the removal of organic species for the first time in the 1970s? A careful examination of ancient works reveals that: (i) The wrong questions were asked during the past three decades, as Fe0 was premised as a reducing agent, (ii) credit for using Fe0 for water treatment belongs to no individual scientist, and (iii) credit for the use of Fe0 in filtration systems for safe drinking water provision belongs to scientists from the 1850s, while credit for the use of Fe0 for the removal of aqueous organic species does not belong to the pioneers of the Fe0 PRB technology. However, it was these pioneers who exploited Fe0 for groundwater remediation, thereby extending its potential. Complementing recent achievements with the chemistry of the Fe0/H2O system would facilitate the design of more sustainable Fe0-remediation systems.

Validating the Efficiency of the FeS2 Method for Elucidating the Mechanisms of Contaminant Removal Using Fe0/H2O Systems

“…In particular, the mechanism discussed here started in 1994 [16], but Khudenko [77] has been completely ignored since then; yet, this should be the starting point. The concept that Fe 0 is an environmental-reducing agent has never been established, as recently demonstrated by Ebelle et al [75], but is still prevailing in both the old and recent literature [84][85][86][87].…”

“…It is hoped that, in establishing that contaminant removals in Fe 0 /H 2 O systems are due to flocculation (adsorption and coprecipitation) ( Figure 6) [89], the results presented herein will redirect the research for the design of the next generation of Fe 0 -based remediation systems, accounting for the ion-selective nature of the systems [14,84,[89][90][91][92]. The view that Fe 0 is a reducing agent [15,93,94] should be immediately abandoned [85]. This view has mediated or supported wrong wordings like zero-valent iron for metallic [14] or reductates for species reducible by Fe 0 according to the relative electrode potentials [94].…”

Characterizing the impact of pyrite addition on the efficiency of Fe0/H2O systems

“…The conclusion of Seng et al 84 supports the view presented herein that the relative kinetics of Fe 0 and FeS 2 oxidation determinate the preponderance of processes in Fe 0 /FeS 2 /H 2 O systems 70 . However, the reported selectivity of the process is questionable as sand and other natural minerals are also covered with FeCPs under similar conditions 29 , 87 – 89 . As an example, Song et al 87 reported on increased Cr VI reduction in Fe 0 /sand/H 2 O systems compared to Fe 0 /H 2 O ones.…”

“…The discussion given herein clearly suggests that if there are differential removal mechanisms, it is due to the differential extent of pH shift. Future research should be designed based on the chemistry of the systems 89 .…”

The Key Role of Contact Time in Elucidating the Mechanism of Enhanced Decontamination by Fe0/mno2/sand Systems

“…Research during the past two decades has rediscovered ltration systems based on metallic iron (Fe 0 ) as an affordable, applicable, and e cient water treatment technology for decentralized water supply (e.g. households and small communities) [3,7,[9][10][11][12][13]. Such Fe 0 lters are only sustainable upon admixing Fe 0 with other aggregates like granular activated carbon, biochar, gravel, magnetite (Fe 3 O 4 ), manganese oxides (MnO x ), pyrite (FeS 2 ), and sand [10,14,15].…”