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Minerals 2016, 6(1), 22; https://doi.org/10.3390/min6010022

The Growth of Gypsum in the Presence of Hexavalent Chromium: A Multiscale Study

1
Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, Universidad de Granada (CSIC, UGR), Avenida de las Palmeras 4, E-18100 Armilla, Granada, Spain
2
Departamento de Cristalografía y Mineralogía, Universidad Complutense de Madrid, C/José Antonio Novais 2, E-28040 Madrid, Spain
3
Instituto de Geociencias, Consejo Superior de Investigaciones Científicas, Universidad Complutense de Madrid (CSIC, UCM), C/José Antonio Novais 2, E-28040 Madrid, Spain
4
Centro de Asistencia a la Investigación de Difracción de Rayos X, Universidad Complutense de Madrid, E-28040 Madrid, Spain
*
Author to whom correspondence should be addressed.
Academic Editor: Athanasios Godelitsas
Received: 12 January 2016 / Revised: 7 March 2016 / Accepted: 8 March 2016 / Published: 15 March 2016
(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)
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Abstract

The sorption of dissolved inorganic pollutants into the structure of minerals is an important process that controls the mobility and fate of these pollutants in the Earth’s crust. It also modifies the surface structure and composition of the host mineral, affecting its crystallization kinetics. Here, we investigate the effect of hexavalent chromium, Cr(VI), on the nucleation and growth of gypsum by conducting two types of experiments: (i) in situ atomic force microscopy (AFM) observations of the growth of gypsum {010} surfaces in the presence of Cr(VI) and (ii) gypsum precipitation experiments by mixing aqueous solutions containing variable amounts of Cr(VI). Gypsum precipitation is progressively delayed when occurring from solutions bearing increasing Cr(VI) concentrations. Chemical analyses of gypsum precipitates show that gypsum incorporates small Cr(VI) amounts that correlate with the content of this ion in the aqueous solution. Gypsum cell parameters variation reflects this incorporation. At the molecular scale, Cr(VI) induces a slowdown of step advance rates on gypsum {010} surfaces accompanied by the roughening of nanostep edges and the so-called “template effect”. This effect involves the reproduction of the original nanotopography after the completion of individual advancing monolayers and appears as a general nanoscale phenomenon occurring during growth of solid solutions from aqueous solutions even in the case of compositionally-restricted solid solutions. View Full-Text
Keywords: hexavalent chromium; gypsum; atomic force microscopy; crystal growth; nucleation; mineral surfaces; template effect hexavalent chromium; gypsum; atomic force microscopy; crystal growth; nucleation; mineral surfaces; template effect
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Morales, J.; Astilleros, J.M.; Matesanz, E.; Fernández-Díaz, L. The Growth of Gypsum in the Presence of Hexavalent Chromium: A Multiscale Study. Minerals 2016, 6, 22.

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