Anisotropic oxidative growth of goethite-coated sand particles in column reactors during 4-chloronitrobenzene reduction by Fe(<scp>ii</scp>)/goethite

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Elucidating how organic matter and iron oxide particles interact will advance the understanding of geochemical processes and facilitate the development and implementation of methods to address groundwater pollution. The sorption and fractionation of three wellcharacterized organic matter isolates, Suwannee River natural organic matter (SRNOM), Suwannee River fulvic acid (SRFA), and Eliot Soil humic acid (ESHA), onto goethite nanoparticles in batch reactors and goethite-coated sand in column reactors were studied. Total organic carbon, molecular size, and optical properties were measured before and after exposure to solids in batch and column reactors, as well as in solution after the resuspension of equilibrated solids in a fresh buffer. Fluorescent, aromatic, high-molecular-weight material more strongly sorbed and stayed sorbed upon exposure to fresh solution. The effects of the different organic matter fractions on reduction of 4-chloronitrobenzene (4-ClNB) were also quantified. In both batch and column reactors, the reactivity of NOM-treated particles toward 4-ClNB in the presence of Fe(II) was inhibited by all isolates as compared to that in NOM-free reactors, with SRFA inhibiting reaction rate constants the most followed by ESHA and SRNOM. There are clear spectral and size differences in the organic matter that remains in the liquid medium compared to the NOM that binds to the mineral surfaces, but both of these materials inhibit Fe(II)-mediated reactions on the surface. Materials high in aliphatic and carboxylate contents, rather than the more strongly sorbing fluorescent aromatic material, appear to inhibit reactivity.

Section: ■ Introductionsupporting

confidence: 73%

Section: Acs Earth Andmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

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Interactions of Goethite and Natural Organic Matter: Fractionation and Impact on Contaminant Reduction

Soroush,

Harris,

Hildebrandt

et al. 2024

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“…Optical analysis showed shard-like granules with a modal diameter of approximately 1.4 μm, though the larger particles, while fewer in number, contributed most to the mass of siderite in the reactors (Figure S1). Compositional analysis was done using inductively coupled plasma–optical emission spectroscopy (ICP-OES) following existing methods, described in the SI . Batch reactors were prepared by adding siderite powder into 37 mL serum bottles equipped with a magnetic stir bar.…”

Section: Methodsmentioning

confidence: 99%

“…Compositional analysis was done using inductively coupled plasma−optical emission spectroscopy (ICP-OES) following existing methods, described in the SI. 71 Batch reactors were prepared by adding siderite powder into 37 mL serum bottles equipped with a magnetic stir bar.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Sulfide Immobilization: Investigating the Impact of a Protective Sulfide-Bearing Layer Formed by Siderite (FeCO₃)

Bingham

McCormick

Penn

2023

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Sulfate-rich wastewater poses ecological hazards to freshwater ecosystems, and sulfate is highly regulated in many Minnesota lakes. Biological sulfate reduction results in the reduction of sulfate to sulfide, and this process is used to remediate acid mine drainage. Theoretically, the aqueous sulfide can be immobilized into a solid-phase material and removed from the aqueous system. This study focuses on sulfide immobilization using iron-bearing waste minerals. Specifically, the extent of reaction of siderite (FeCO 3 ), an abundant ferrous mineral in some mining wastes, with sulfide was studied. Mildly acidic batch reactors containing powdered siderite were consecutively injected with a sodium sulfide solution. Solid reaction products were identified and characterized using powder X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive Xray spectroscopy. Mackinawite (FeS) appeared to be the most abundant product, with greigite (Fe 3 S 4 ) also detected. Results reveal that the immobilization capacity of sulfide by siderite is limited by the concentration of the Fe 2+ (aq) presented in the system immediately before the initial sulfide exposure as the Fe 2+ (aq) levels are not replenished after sulfidation. These results improve our understanding of the sulfidation of siderite and provide insight to improve the viability of using siderite-containing mining waste rock in a sulfate remediation technology.

Reductive Degradation of 4-Chloronitrobenzene by Fe(II) on Aluminum-Substituted Goethite Nanoparticles

Johnston,

Wiethorn,

Combs

et al. 2024

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Iron oxide minerals play important roles in geo-and environmental chemistry, with substantial impacts on the chemical, physical, and (micro)biological properties of soils and also the behavior, fate, and transport of pollutants. The trivalent aluminum cation is commonly found substituted in natural iron oxides as a result of its abundance in soil and its similarity in both charge and size compared to ferric ion. Here, we examine the impact of aluminum substitution on the reactivity of Fe(II) on the iron oxide mineral goethite toward 4-chloronitrobenzene (4-ClNB), which serves as the oxidant and model pollutant. The impact of aluminum substitution on both the kinetics of contaminant reduction and the concurrent oxidative mineral growth of goethite were quantified. Rate constants were determined using both the Langmuir−Hinshelwood−Haugen−Watson (LHHW) equation and a pseudo-first-order model applied to data obtained from reactors prepared using initial concentrations of 4-ClNB from 10 to 100 μM. LHHW more accurately describes the kinetics of the reduction of 4-ClNB by Fe(II) on goethite nanoparticles and provides insights into the nature of the reactivity of goethite nanocrystals. Results demonstrate that low levels of aluminum substitution (≤4 mol % Al) result in increased reactivity, as quantified by transmission electron microscopy surface-area-normalized pseudo-first-order rate constants, and that higher levels of aluminum substitution (>4 mol % Al) result in a decrease in reactivity. In addition, aluminum substitution does not impact the surface on which the oxidative mineral growth occurs, with goethite nanoparticle lengths increasing without a concurrent increase in width observed over all particle compositions.