Validating the Efficiency of the FeS$_2$ Method for Elucidating the Mechanisms of Contaminant Removal Using Fe$_0$/H$_2$O Systems
Citable Link (URL):http://resolver.sub.uni-goettingen.de/purl?gs-1/17594
There is growing interest in using pyrite minerals (FeS$_2$) to enhance the efficiency of metallic iron (Fe$^0$) for water treatment (Fe$^0$/H$_2$O systems). This approach contradicts the thermodynamic predicting suppression of FeS$_2$ oxidation by Fe$^0$ 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 Fe$^0$ corrosion in Fe$^0$/H$_2$O systems. The effects of the addition of various amounts of FeS$_2$ to a Fe$^0$/sand mixture (FeS$_2$ method) on MB discoloration were characterized in parallel quiescent batch experiments for up to 71 d (pH$_0$ = 6.8). Pristine and aged FeS$_2$ 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 FeS$_2$ induces a pH shift and delays Fe precipitation and sand coating. Pristine FeS$_2$ induced a pH shift to values lower than 4.5, but no quantitative MB discoloration occurred after 45 d. Aged FeS$_2$ 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 Fe$^0$/H$_2$O systems. This research has clarified the reason why a FeS$_2$ addition enhances the efficiency of Fe$^0$ environmental remediation.
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