Influence of Surface Compositions on the Reactivity of Pyrite toward Aqueous U(VI)

Ma, Bin; Fernández-Martı́nez, Alejandro; Kang, Mingliang; Wang, Kaifeng; Lewis, Aled R.; Maffeïs, Thierry G.G.; Findling, Nathaniel; Salas‐Colera, Eduardo; Tisserand, Delphine; Bureau, Sarah; Charlet, Laurent

doi:10.1021/acs.est.0c01854

Cited by 28 publications

(4 citation statements)

References 69 publications

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“…Meanwhile, in well-buffered circumneutral environments such as fresh water sediments, salt marsh, and wastewater remediation, − the pyrite oxidation process and the generate pathway of ROS (i.e., • OH) are entirely different thanks to the hydrolytic precipitation of Fe(III) and the inhibition of the homogeneous Fenton process. Most of the current studies emphasized the indispensable role of surface-adsorbed ferrous ions (hereinafter referred to as Fe( II ) ad ) on pyrite oxidation, − corresponding to the Extending Singer–Stumm Model proposed by Moses and Herman in 1991, who point that the presence of Fe( II ) ad accelerates pyrite oxidation and describe Fe( II ) ad as the electron transfer “conduit” between pyrite and oxidants . Zhang et al.…”

Section: Introductionmentioning

confidence: 99%

Redox Behavior of Secondary Solid Iron Species and the Corresponding Effects on Hydroxyl Radical Generation during the Pyrite Oxidation Process

Zhao

Peng

et al. 2022

Environ. Sci. Technol.

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During the pyrite oxidation process, aqueous ferrous/ferric ions (Fe 2+ /Fe 3+ ), as well as surface-adsorbed Fe 2+ /Fe 3+ , have been widely recognized to dominate hydroxyl radical ( • OH) generation, while this study reveals that the secondary solid iron species also play nonnegligible roles. Based on the different forms and the presence of sites, the secondary solid iron species were classified as Fe coat (iron-containing coating on the pyrite surface) and Fe dep (ex situ-deposited iron (oxyhydr)oxide that is not in contact with pyrite). Instead of participating in building a stubborn passivation layer on the pyrite surface, Fe coat is easy to fall off from the pyrite surface as the oxidation of pyrite deepens, while large fractions of Fe dep and Fe coat are found to be extractable with nitrilotriacetic acid (NTA). Achieved by cyclically oxidizing pyrite within different NTA levels (0/0.1/10 mM), Fe coat and Fe dep were proved to have distinct redox behavior during the pyrite oxidation process. Amorphous Fe dep , originated from the hydrolyzation of dissolved Fe 3+ , accelerates the nonradical decay of hydrogen peroxide (H 2 O 2 ); as a result, the accumulation of Fe dep always decreases the • OH production during the pyrite oxidation process. However, part of Fe dep adsorbs on the pyrite surface through electrostatic attraction and converts into Fe coat . The electron conduction between Fe coat and pyrite was verified, which accelerates the oxidative dissolution of pyrite, produces reactive Fe(II), and therefore favors • OH generation. This study improves our understanding of the redox behavior of pyrite in complex media such as natural processes and practical engineering systems.

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Section: Introductionmentioning

confidence: 99%

Redox Behavior of Secondary Solid Iron Species and the Corresponding Effects on Hydroxyl Radical Generation during the Pyrite Oxidation Process

Zhao

Peng

et al. 2022

Environ. Sci. Technol.

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“…Among all the cementitious materials in engineered barriers and all the naturally occurring minerals in the surrounding geologic formations, only a few have the ability to uptake selenium oxyanions via either adsorption processes or reductive precipitation. These are, e.g., layered double hydroxides such as the hydrotalcite phases in cements (AFm), and the redox-active Fe(II)-bearing phases present as the result of corrosion of the steel containers or naturally in minerals such as pyrite, mackinawite, magnetite, or Fe(II)-bearing clay minerals. − Abiotic reduction of soluble selenium species by Fe(II)-bearing materials (potential steel corrosion products) has been observed for several minerals such as green rust, − magnetite, ,, mackinawite and siderite, pyrite, , troilite, and zero-valent iron . The mixed-valence Fe(II)/(III) oxide magnetite (Fe 3 O 4 ) has showed redox reactivity toward selenium species. ,, Magnetite nanoparticles have been shown to reduce Se(IV) and Se(VI) to elemental selenium and iron selenides, , even in the presence of oxidized layers or maghemite and coatings. , The product of these redox processes is a partially oxidized magnetite, i.e., a magnetite particle containing some proportion of maghemitean Fe(III) mineral isostructural to magnetite, a phase that is also able to adsorb selenium oxyanions. , …”

Section: Introductionmentioning

confidence: 99%

Selenium Nanowire Formation by Reacting Selenate with Magnetite

Poulain

Fernández-Martı́nez

Grenèche

et al. 2022

Environ. Sci. Technol.

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The mobility of 79 Se, a fission product of 235 U and longlived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se(VI)O 4 2− ) and selenite (Se(IV)O 3 2−) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids. Here, we investigated the sorption and reduction capacity of synthetic nanomagnetite toward Se(VI) at neutral and acidic pH, under reducing, oxygen-free conditions. The additional presence of Fe(II) aq , released during magnetite dissolution at pH 5, has an effect on the reduction kinetics. X-ray absorption spectroscopy analyses revealed that, at pH 5, trigonal gray Se(0) formed and that sorbed Se(IV) complexes remained on the nanoparticle surface during longer reaction times. The Se(0) nanowires grew during the reaction, which points to a complex transport mechanism of reduced species or to active reduction sites at the tip of the Se(0) nanowires. The concomitant uptake of aqueous Fe(II) and Se(VI) ions is interpreted as a consequence of small pH oscillations that result from the Se(VI) reduction, leading to a re-adsorption of aqueous Fe(II) onto the magnetite, renewing its reducing capacity. This effect is not observed at pH 7, where we observed only the formation of Se(0) with slow kinetics due to the formation of an oxidized maghemite layer. This indicates that the presence of aqueous Fe(II) may be an important factor to be considered when examining the environmental reactivity of magnetite.

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“…Actinyl ions can be immobilized on redox-active iron sulfide minerals. For instance, pyrite − has been explored using theoretical and experimental studies . The presence of DOM or carbonate has been found to decrease the formation of U(IV) on pyrite surfaces because uranyl ions form stable complexes and the reduction is inhibited.…”

Section: Introductionmentioning

confidence: 99%

“…For instance, pyrite 14−27 has been explored using theoretical and experimental studies. 28 The presence of DOM or carbonate has been found to decrease the formation of U(IV) on pyrite surfaces 26 because uranyl ions form stable complexes and the reduction is inhibited. Furthermore, dissolution of UO 2 (s) has been reported to increase with increasing concentrations of DOM under reducing conditions.…”

Section: Introductionmentioning

confidence: 99%

Actinyl Adsorption and Reduction on Pyrite Surfaces: Insights from DFT Calculations

Arumugam

Kim

Becker

2022

ACS Earth Space Chem.

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Interactions of actinides with pyrite surfaces are highly important in catalyzing their reductive immobilization, thereby controlling the movement of these species in the environment. Here, surface adsorption and subsequent reduction of aqueous actinyl(VI) on pyrite surfaces were explored using density functional hybrid theory (DFT-B3LYP) combined with a first hydration sphere of water molecules and a dielectric continuum for solvation effects. Adsorption of cationic (AnO2(H2O)5)2+(An = U, Np, Pu) and neutral AnO2(OH)2(H2O)3 actinyl onto a small pyrite cluster (Fe4S8) and the effect of coadsorption on the energetics and electron transfer are evaluated by adding either hydroquinone, H2Q (reduced), or quinone, Q (oxidized). The pyrite surface instantaneously transfers an electron to the adsorbed cationic actinyl. Unpaired electron atomic spin densities confirm the electron transfer from the pyrite surface to An atoms. For the neutral actinyl adsorption, electron transfer is confirmed for neptunyl and plutonyl but not for uranyl. Several factors control the overall adsorption energetics and kinetics, such as the nature of the coadsorbate (H2Q/Q), pyrite surface, actinyl, and charge or protonation state (cationic or neutral). The surface-mediated reduction of adsorbed actinyl occurs by receiving electrons either directly from the sulfide or from the coadsorbed H2Q through the sulfide. In the direct reduction case, an H+ ion is added to the surface-bound cationic actinyl, and the mineral surface acts as an electron donor. In contrast, in the proton-coupled electron transfer (PCET) reduction, the surface mediates the electrons through the surface by synergistically aligning relevant orbitals in line. This results in the less soluble and stable An(IV). Our results indicate that the pyrite surface promotes a faster PCET reaction for the actinyl reduction under circumneutral (pH 4–7) conditions.

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Influence of Surface Compositions on the Reactivity of Pyrite toward Aqueous U(VI)

Cited by 28 publications

References 69 publications

Redox Behavior of Secondary Solid Iron Species and the Corresponding Effects on Hydroxyl Radical Generation during the Pyrite Oxidation Process

Redox Behavior of Secondary Solid Iron Species and the Corresponding Effects on Hydroxyl Radical Generation during the Pyrite Oxidation Process

Selenium Nanowire Formation by Reacting Selenate with Magnetite

Actinyl Adsorption and Reduction on Pyrite Surfaces: Insights from DFT Calculations

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