Scorodite Synthesis in As(V)-Containing Fe(II) Solution in the Presence of Hematite as a Fe(III) Source

Iizuka, Atsushi; Shinoda, Kōzō; Shibata, Etsuro

doi:10.2320/matertrans.m-m2018809

Cited by 14 publications

(17 citation statements)

References 7 publications

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“…5) It was also suggested that hematite-seeds paly a role as the Fe 3+ source for scorodite formation. 10) In our biogenic studies, the positive effect of scoroditeseeds was also noted. 11,17) Since biomineralization reactions involve the interactions between the mineral, microbial cells (physicochemical as well as enzymatic effects) and reactant ions, the function of seed minerals within the biomineralization process can be complex.…”

Section: ¹supporting

confidence: 58%

“…Therefore, the two-stage Asremoval was indeed found to play an important role in effective biogenic scorodite crystallization. 18) In abiotic scorodite crystallization studies by other researchers, the effect of seed-feeding (homogeneous scorodite or other heterogeneous minerals) was shown to be one of the influential factors: 3,5,10,19) Feeding scoroditeseeds allowed lowering the reaction temperature for scorodite crystallization (from 95 to 80°C). 3) Use of heterogeneousseeds such as hematite and gypsum were shown to be equally effective as homogeneous scorodite-seeds, where the authors suggested that hematite can outperform scorodite due to its "fine" properties.…”

Section: ¹mentioning

confidence: 99%

“…In the DMSP reaction using hematite-seeds, the overall Fe 2+ concentration in the system was reported to be constant: The authors, therefore, suggested that Fe 2+ ions once incorporated into the gel-like Fe 2+ -As(V) precursors are then released upon their conversion to crystalline scorodite by reacting with Fe 3+ deriving from hematite. 10) In the process of our biogenic reaction using Ac. brierleyi (70°C), the oxidation of Fe 2+ and As(III) mostly precede the precipitation of Fe and As.…”

Section: ¹mentioning

confidence: 99%

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The Effect of Heterogeneous Seed Crystals on Arsenite Removal as Biogenic Scorodite

et al. 2020

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With the aim to effectively oxidize and remove highly toxic As(III) from acidic metal-refinery wastewaters, the seeding effect of different heterogeneous minerals was investigated on the formation of biogenic scorodite (FeAsO 4 •2H 2 O), using the Fe 2+ /As(III)-oxidizing thermoacidophilic archaeon Acidianus brierleyi. Heterogeneous hematite-seeds exhibited even greater As-removal efficiency relative to homogeneous scorodite-seeds. While the effect of magnetite-seeds was mostly comparable to scorodite-seeds, feeding goethite or ferrihydrite negatively affected the speed of As precipitation, forming jarosite or jarosite/scorodite mixture, respectively, instead of scorodite. Similarly to those formed on scorodite-seeds (TCLP As leachability; 0.49 mg/L), the final scorodite products formed on hematite-seeds or magnetite-seeds were also highly stable (0.51 mg/L or 0.39 mg/L, respectively), well below the US standard of 5 mg/L. The effectiveness of hematite seeding was also demonstrated in the lower-temperature scorodite crystallization reaction (45°C), where Fe 2+-oxidizing moderately-thermophilic acidophilic bacterium Acidimicrobium ferrooxidans was employed, after the complete As(III) oxidation by Thiomonas cuprina. The overall results suggested that the effectiveness of hematite was, at least partly, attributed to its highly-positive surface charge. This effect was retained even when cells attached onto the hematite surface. This made the mineral an effective absorbent for anionic As(V) and SO 4 2¹ , consequently speeding up the reaction by shortening the steady-state induction period between the two As-removal stages, during the biogenic scorodite crystallization process.

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Section: ¹supporting

confidence: 58%

Section: ¹mentioning

confidence: 99%

Section: ¹mentioning

confidence: 99%

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The Effect of Heterogeneous Seed Crystals on Arsenite Removal as Biogenic Scorodite

et al. 2020

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“…The reaction also occurs through gel-like precursor generation and its conversion to scorodite. In a previous study, 34) it was reported that the precursor contains Fe(II) as well as Fe(III). Furthermore, when Fe(II) is not contained in the solution, the formation reaction does not proceed even if hematite is added.…”

Section: Introductionmentioning

confidence: 97%

Investigation of the Scorodite Formation Mechanism in As(V) Solution Containing Fe(II) with Hematite Addition Using a Stable Iron Isotope

2022

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Arsenic is a toxic element, and development of effective methods for As removal and stabilization are necessary. Removal and stabilization of pentavalent As as crystalline scorodite (FeAsO 4 •2H 2 O) is a promising method for As treatment of industrial byproducts. When hematite (Fe(III) 2 O 3 ) powder is added to As(V) solution containing Fe(II) under appropriate conditions, scorodite crystals form from the gel-like precursor. When Fe(II) is not contained in the solution, the formation reaction does not proceed, even if hematite is added. Therefore, it is considered that the Fe(II) in the solution is heavily involved in the formation mechanism. Here, to elucidate the scorodite crystal formation mechanism in the hematite addition method, the origin of the iron in scorodite was investigated through scorodite synthesis experiments with addition of a stable iron isotope ( 54 Fe) to the reaction solution. It was estimated that the Fe(III) constituting the scorodite crystals was mainly (more than about 80 atom%) derived from the Fe(II) in the solution. From this result, scorodite formation from the reaction solution with solid hematite can be considered to occur as follows. The gel-like precursor is composed of Fe(II) from the reaction solution together with Fe(III) from hematite. During conversion of the gel-like precursor to scorodite crystals, Fe(II) in the precursor is oxidized by Fe(III), and it then combines with the arsenate ion to form scorodite. With conversion to scorodite crystals, the Fe(II) generated by this electron exchange (originally from hematite) dissolves in the reaction solution. It is speculated that electron exchange between solution-derived Fe(II) and hematite-derived Fe(III) plays an important role in formation of scorodite crystals in this synthetic method.

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“…Scorodite synthesis by direct addition of solid Fe(III) compounds, namely hematite (Fe 2 O 3 ) 24,26,27) and magnetite (Fe 3 O 4 ), 28,29) to an FeSO 4 solution containing As(V) has also been reported. For hematite addition, the overall scorodite formation reaction can be expressed as shown in eq.…”

Section: Introductionmentioning

confidence: 99%

Scorodite Crystal Formation on Hematite (Fe<sub>2</sub>O<sub>3</sub>) Surface in Fe(II) Solution Containing As(V)

2020

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Scorodite crystal formation on a hematite (Fe 2 O 3) surface in excess Fe(II) solution containing As(V) was observed under various conditions using the direct hematite addition method. Gel-like precursors initially formed and covered the entire hematite surface. Scorodite crystal nuclei then appeared preferentially on the grain boundaries of each hematite crystal, rather than on the flat hematite crystal surface. These grew into faceted crystalline scorodite particles through stepwise structure formation. The effects of solution temperature (50, 70, and 95°C), initial solution pH (0.6, 0.9, and 1.6), initial Fe(II) concentration (0, 25, and 55.9 g/L), and initial As concentration (25 and 50 g/L) on gel-like precursor and scorodite crystal formation were comprehensively investigated. The reaction temperature only affected the scorodite crystal formation rate and not the crystal shape in the studied range of 5095°C. Octahedral faceted scorodite was obtained at all temperatures studied. The solution pH strongly affected scorodite crystal formation, with a higher pH favoring scorodite formation in the studied range of pH 0.61.6. Scorodite crystals were not obtained at pH 0.6 because of the lower AsO 4 3¹ concentration in solution. Octahedral faceted scorodite crystals were also obtained at a lower Fe(II) concentration (25 g/L), but the gel-like precursor and scorodite crystals were not obtained in the absence of Fe(II). The As(V) concentration in solution affected the overall scorodite formation rate. Imperfect octahedral-shaped scorodite crystals with larger diameters were observed at lower As(V) concentration (25 g/L), which was attributed to the lower AsO 4 3¹ concentration. This study provides important information for As treatment through scorodite crystal formation using the hematite addition method.

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Scorodite Synthesis in As(V)-Containing Fe(II) Solution in the Presence of Hematite as a Fe(III) Source

Cited by 14 publications

References 7 publications

The Effect of Heterogeneous Seed Crystals on Arsenite Removal as Biogenic Scorodite

The Effect of Heterogeneous Seed Crystals on Arsenite Removal as Biogenic Scorodite

Investigation of the Scorodite Formation Mechanism in As(V) Solution Containing Fe(II) with Hematite Addition Using a Stable Iron Isotope

Scorodite Crystal Formation on Hematite (Fe<sub>2</sub>O<sub>3</sub>) Surface in Fe(II) Solution Containing As(V)

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