Structural Incorporation of As⁵⁺ into Phosphosiderite by a Strengite/Scorodite–like Arrangement

Author(s)

Ralph M. Bolanz, Maria Wierzbicka-Wieczorek, Gerald Giester, Jörg Göttlicher, Ralph Steininger

Abstract

Phosphosiderite (FePO4·2H2O) is the monoclinic (P21/n) polymorph of orthorhombic strengite (Pbca), which is isostructural to scorodite (FeAsO4·2H2O). While the structural incorporation of As5+ into strengite can be attributed to a fractional miscibility between strengite and scorodite, the incorporation of As5+ into phosphosiderite and its dehydration product FePO4 (P 21/n) has never been investigated until now. Phosphosiderite, synthesized under hydrothermal conditions at 200?°C in the presence of arsenic, incorporates 0.044±0.001, 0.084±0.001, 0.165±0.002, 0.425±0.004 and 0.844±0.014 wt.% As at initial molar As/Fe solution ratios of 0.05, 0.1, 0.2, 0.5 and 1, respectively. With increasing As content, the P concentration in phosphosiderite decreases by 1.02 to 1.58 P atoms for each incorporated As. The unit-cell parameters a, b, c and ß increase from As-free phosphosiderite with 5.326(6) Å, 9.793(8) Å, 8.709(3) Å and 90.54(0)° to 5.329(0) Å, 9.797(5) Å, 8.713(7) Å and 90.56(7)°, respectively, for phosphosiderite synthesized at an initial molar As/Fe solution ratio of 1. Single crystal X-ray diffraction indicates that the P position in phosphosiderite is occupied by As with about 2?%. X-ray absorption spectroscopy displays only As5+, which resides on the P position in phosphosiderite in a local coordination similar to strengite and scorodite, indicating the structural incorporation of As5+ into a strengite/scorodite-like arrangement.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Friedrich-Schiller-Universität Jena, Karlsruher Institut für Technologie

Journal

Chemistry SELECT

Volume

1

Pages

4152–4160

No. of pages

9

ISSN

2365-6549

DOI

https://doi.org/10.1002/slct.201600884

Publication date

09-2016

Peer reviewed

Yes

Austrian Fields of Science 2012

105116 Mineralogy, 104011 Materials chemistry, 105113 Crystallography

Keywords

ASJC Scopus subject areas

General Chemistry

Portal url

https://ucrisportal.univie.ac.at/en/publications/b47fce77-43ac-4f25-a587-020a376eec0f