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

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

1
School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing 211100, China
2
Biosystems and Environmental Engineering Research Group, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare 921, Zimbabwe
3
Applied Geology, University of Göttingen, Goldschmidtstraße 3, D-37077 Göttingen, Germany
4
Centre for Modern Indian Studies (CeMIS), University of Göttingen, Waldweg 26, D-37073 Göttingen, Germany
*
Authors to whom correspondence should be addressed.
Processes 2020, 8(9), 1162; https://doi.org/10.3390/pr8091162
Received: 5 August 2020 / Revised: 22 August 2020 / Accepted: 11 September 2020 / Published: 16 September 2020
There is growing interest in using pyrite minerals (FeS2) to enhance the efficiency of metallic iron (Fe0) for water treatment (Fe0/H2O systems). This approach contradicts the thermodynamic predicting suppression of FeS2 oxidation by Fe0 addition. Available results are rooted in time series correlations between aqueous and solid phases based on data collected under various operational conditions. Herein, the methylene blue method (MB method) is used to clarify the controversy. The MB method exploits the differential adsorptive affinity of MB onto sand and sand coated with iron corrosion products to assess the extent of Fe0 corrosion in Fe0/H2O systems. The effects of the addition of various amounts of FeS2 to a Fe0/sand mixture (FeS2 method) on MB discoloration were characterized in parallel quiescent batch experiments for up to 71 d (pH0 = 6.8). Pristine and aged FeS2 specimens were used. Parallel experiments with methyl orange (MO) and reactive red 120 (RR120) enabled a better discussion of the achieved results. The results clearly showed that FeS2 induces a pH shift and delays Fe precipitation and sand coating. Pristine FeS2 induced a pH shift to values lower than 4.5, but no quantitative MB discoloration occurred after 45 d. Aged FeS2 could not significantly shift the pH value (final pH ≥ 6.4) but improved the MB discoloration. The used systematic sequence of experiments demonstrated that adsorption and coprecipitation are the fundamental mechanisms of contaminant removal in Fe0/H2O systems. This research has clarified the reason why a FeS2 addition enhances the efficiency of Fe0 environmental remediation. View Full-Text
Keywords: dye discoloration; FeS2 method; MB method; removal mechanism; zero-valent iron dye discoloration; FeS2 method; MB method; removal mechanism; zero-valent iron
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Xiao, M.; Cui, X.; Hu, R.; Gwenzi, W.; Noubactep, C. Validating the Efficiency of the FeS2 Method for Elucidating the Mechanisms of Contaminant Removal Using Fe0/H2O Systems. Processes 2020, 8, 1162.

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