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Minerals 2019, 9(1), 27; https://doi.org/10.3390/min9010027

Crystallization Behaviour of Iron-Hydroxide Sulphates by Aging under Ambient Temperature Conditions

Department of Geology, University of Oviedo, 33005 Oviedo, Spain
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Received: 11 December 2018 / Revised: 27 December 2018 / Accepted: 4 January 2019 / Published: 5 January 2019
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Abstract

The crystallization behaviour of jarosite and schwertmannite has been studied by precipitation-aging experiments performed using different parent-solution concentrations at acidic conditions and ambient temperature. Schwertmannite exhibits low crystallinity and is the only mineral identified during low-concentration (LC) experiments. However, in high-concentration (HC) experiments, a relatively rapid Ostwald ripening process leads to the transformation of schwertmannite into natrojarosite. The presence of sodium modifies the morphology and stability of the obtained phases. TEM observations reveal that schwertmannite particles consist of disoriented nanodomains (~6 nm) spread in an amorphous mass. In contrast, natrojarosite particles exhibit a single-domain, highly crystalline core, with the crystallinity decreasing from core to rim. The thermal behaviour of these phases depends on both their composition and their degree of crystallinity. TG and DTG analyses show that, below 500 °C, the amount of structural water is clearly higher in schwertmannite than in natrojarosite. The present results highlight the role of the ripening processes in epigenetic conditions and could be important in interpreting the formation of jarosite in Earth and Martian surface environments. View Full-Text
Keywords: jarosite; schwertmannite; morphology; precipitation; decomposition behaviour; supergene jarosite; schwertmannite; morphology; precipitation; decomposition behaviour; supergene
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Jiménez, A.; Hernández, A.; Prieto, M. Crystallization Behaviour of Iron-Hydroxide Sulphates by Aging under Ambient Temperature Conditions. Minerals 2019, 9, 27.

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