Partial frustration of magnetic order in synthetic angelellite, Fe4As2O11 †

Wright, J.P.; Mclaughlin, Abbie C.; Attfield, J. Paul

doi:10.1039/b005350n

Cited by 7 publications

(5 citation statements)

References 6 publications

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“…A minor impurity within the angelellite sample was tentatively identified as FeAsO 4 . The formation of this iron arsenate during the angelellite synthesis, described by ref , yields a fraction of 9.5(7) wt %.…”

Section: Resultsmentioning

confidence: 97%

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Structural Incorporation of As⁵⁺ into Hematite

Bolanz

Wierzbicka‐Wieczorek

Čaplovičová

et al. 2013

Environ. Sci. Technol.

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Hematite (α-Fe2O3) is one of the most common iron oxides and a sink for the toxic metalloid arsenic. Arsenic can be immobilized by adsorption to the hematite surface; however, the incorporation of As in hematite was never seriously considered. In our study we present evidence that, besides adsorption, the incorporation of As into the hematite crystals can be of great relevance for As immobilization. With the coupling of nanoresolution techniques and X-ray absorption spectroscopy the presence of As (up to 1.9 wt %) within the hematite crystals could be demonstrated. The incorporated As(5+) displays a short-range order similar to angelellite-like clusters, epitaxially intergrown with hematite. Angelellite (Fe4As2O11), a triclinic iron arsenate with structural relations to hematite, can epitaxially intergrow along the (210) plane with the (0001) plane of hematite. This structural composite of hematite and angelellite-like clusters represents a new immobilization mechanism and potentially long-lasting storage facility for As(5+) by iron oxides.

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Section: Resultsmentioning

confidence: 97%

“…Pure angelellite was synthesized after the work of Wright et al, 13 but the temperature of 700 °C was maintained for 36 h instead of 12 h, since the reactants were still present after 12 h.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Structural Incorporation of As⁵⁺ into Hematite

Bolanz

Wierzbicka‐Wieczorek

Čaplovičová

et al. 2013

Environ. Sci. Technol.

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“…The small amount of water is certainly physisorbed, but even this small amount accounts for a correction of 1.2 kJ·mol –1 . The possibility of structural OH groups was entertained by Moore and Araki (1978), but rejected by detailed neutron diffraction studies (Wright et al ., 2000). The calculated enthalpy of formation from the elements at standard conditions is –2625.7 ± 7.3 kJ·mol –1 for the composition Fe 4 (AsO 4 ) 2 O 3 .…”

Section: Resultsmentioning

confidence: 99%

“…A sample that mostly contained angelellite was synthesized after a modified procedure of Wright et al (2000). Briefly, 4.182 g (18.2 mmol) of anhydrous As 2 O 5 and 29.943 g (74.1 mmol) Fe(NO 3 ) 3 ·9H 2 O were dissolved in 500 mL of 2 M nitric acid (HNO 3 ) (65%) and boiled under a fume hood to dryness.…”

Section: Methodsmentioning

confidence: 99%

“…To remove an FeAsO 4 impurity (cf. Wright et al , 2000), the dried sample was mixed with 200 mL of 18% (by mass) hydrochloric acid (HCl), and the suspension was stirred at room temperature for 2 h. The solution turned increasingly yellow, indicating liberation of Fe 3+ from the sample. After 2 h, the suspension was filtered and washed with 500 mL of deionized water and air-dried.…”

Section: Methodsmentioning

confidence: 99%

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Thermodynamic properties of mansfieldite (AlAsO₄·2H₂O), angelellite (Fe₄(AsO₄)₂O₃) and kamarizaite (Fe₃(AsO₄)₂(OH)₃·3H₂O)

et al. 2018

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Thermodynamic data for the arsenates of various metals are necessary to calculate their solubilities and to evaluate their potential as arsenic storage media. If some of the less common arsenate minerals have been shown to be less soluble than the currently used options for arsenic disposal (especially scorodite and arsenical iron oxides), they should be further investigated as promising storage media. Furthermore, the health risk associated with arsenic minerals is a function of their solubility and bioavailability, not merely their presence. For all these purposes, solubilities of such minerals need to be known. In this work, a complete set of thermodynamic data has been determined for mansfieldite, AlAsO4·2H2O; angelellite, Fe4(AsO4)2O3; and kamarizaite, Fe3(AsO4)2(OH)3·3H2O, using a combination of high-temperature oxide-melt calorimetry, relaxation calorimetry, solubility measurements, and estimates where possible and appropriate. Several choices for the reference compounds for As for the high-temperature oxide-melt calorimetry were assessed. Scorodite was selected as the best one. The calculated Gibbs free energy of formation (all data in kJ·mol–1) is –1733.4 ± 3.5 for mansfieldite, –2319.2 ± 7.9 for angelellite and –3056.8 ± 8.5 for kamarizaite. The solubility products for the dissolution reactions are –21.4 ± 0.5 for mansfieldite, –43.4 ± 1.5 for angelellite and –50.8 ± 1.6 for kamarizaite. Available, but limited, chemical data for the natural scorodite–mansfieldite solid-solution series hint at a miscibility gap; hence the non-ideal nature of the series. However, no mixing parameters were derived because more data are needed. The solubility of mansfieldite is several orders of magnitude higher than that of scorodite. The solubility of kamarizaite, on the other hand, is comparable to that of scorodite, and kamarizaite even has a small stability field in a pH-pε diagram. It is predicted to form under mildly acidic conditions in acid drainage systems that are not subject to rapid neutralization and sudden strong supersaturation. The solubility of angelellite is high, and the mineral is obviously restricted to unusual environments, such as fumaroles. Its crystallization may be enhanced via its epitaxial relationship with the much more common hematite. The use of the scorodite–mansfieldite solid solution for arsenic disposal, whether the solid solution is ideal or not, is not practical. The difference in solubility products of the two end-members (scorodite and mansfieldite) is so large that almost any system will drive the precipitation of essentially pure scorodite, leaving the aluminium in the aqueous phase.

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