Mechanochemically Sulfidated Microscale Zero Valent Iron: Pathways, Kinetics, Mechanism, and Efficiency of Trichloroethylene Dechlorination

Abstract

In water treatment processes that involve contaminant reduction by zerovalent iron (ZVI), reduction of water to dihydrogen is a competing reaction that must be minimized to maximize the efficiency of electron utilization from the ZVI. Sulfidation has recently been shown to decrease H formation significantly, such that the overall electron efficiency of (or selectivity for) contaminant reduction can be greatly increased. To date, this work has focused on nanoscale ZVI (nZVI) and solution-phase sulfidation agents (e.g., bisulfide, dithionite or thiosulfate), both of which pose challenges for up-scaling the production of sulfidated ZVI for field applications. To overcome these challenges, we developed a process for sulfidation of microscale ZVI by ball milling ZVI with elemental sulfur. The resulting material (S-mZVI) exhibits reduced aggregation, relatively homogeneous distribution of Fe and S throughout the particle (not core-shell structure), enhanced reactivity with trichloroethylene (TCE), less H formation, and therefore greatly improved electron efficiency of TCE dechlorination (ε). Under ZVI-limited conditions (initial Fe/TCE = 1.6 mol/mol), S-mZVI gave surface-area normalized reduction rate constants (k') and ε that were ∼2- and 10-fold greater than the unsulfidated ball-milled control (mZVI). Under TCE-limited conditions (initial Fe/TCE = 2000 mol/mol), sulfidation increased k and ε ≈ 5- and 50-fold, respectively. The major products from TCE degradation by S-mZVI were acetylene, ethene, and ethane, which is consistent with dechlorination by β-elimination, as is typical of ZVI, iron oxides, and/or sulfides. However, electrochemical characterization shows that the sulfidated material has redox properties intermediate between ZVI and FeO, mostly likely significant coverage of the surface with FeS.

Palygorskite-supported sulfide-modified nanoscale zero-valent iron for Congo red removal

“…The polysulfide species disclosed that some oxidation of the surface S 2might have happened [29,30]. As calculated, the contents of S 2and S n 2are 37.5% and 36.42%, respectively, which is consistent with previous studies [19,22]. Due to the surface sulfidation, Fe 0 would be oxidized into different valence states, and the content of Fe 0 will affect the reduction efficiency of the target pollutant.…”

“…Orange I removal k obs rate of S-nZVI is 71.8 times higher than the one without sulfidation [21]. Many results showed that sulfidation conditions had great effects on target pollutants degradation efficiency [15,17,19,20]. For example, Cao et al found that the removal of antibiotic florfenicol was strongly dependent on S/Fe and the surface-areanormalized reaction rate constant of antibiotic florfenicol on S-nZVI at the optimal S/Fe molar ratio (0.14) was 48 times higher than nZVI [22].…”

“…The sulfide of nZVI can be achieved by adding dithionite in the reducing process of ferric chloride by sodium borohydride. Han et al and Gu et al reported that Fe/FeS could be formed through the addition of dithionite during borohydride reduction of ferric chloride, and Fe/FeS showed an enhanced degradation rate towards trichloroethene (TCE) [16,19]. S-nZVI, obtained from a similar process, was also effective in treating Cd, and the removal capacity could be up to 85 mg/g [20].…”

Quantifying the efficiency and selectivity of organohalide dechlorination by zerovalent iron

“…20 The latter may be adequate for some purposes, but there are many possible reasons why this could give misleading results. However, there also are ways this issue can be turned into an advantage, such as in the systematic comparison of efficiencies obtained under halocarbon-vs. ZVIlimiting conditions, 29 which is discussed below.…”

Insight into Different Mechanisms for Oxidation of Liquid and Gaseous Pollutants by Bi−NaBiO3 with or without Visible Light Illumination

“…Zero valent iron (ZVI) is one of the most popular materials used for purification of polluted water in Dark because it could reductive removal of organics or oxidation of chemicals worked as Fentonlike system in the presence of dissolved O 2 or H 2 O 2 . [18][19][20] However, many kinds of intermediates were produced during reductive process causing secondary pollution. And, the consuming added oxidant in oxidation process could increase excess cost.…”