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Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

DOI: 10.3390/min7080140 DOI Help

Authors: Mercedes Ossorio (LEC, IACT, CSIC, Universidad de Granada) , Tomasz M. Stawski (GFZ German Research Centre for Geosciences) , Juan Rodríguez-blanco (Trinity College Dublin) , Mike Sleutel (Flanders Interuniversity Institute for Biotechnology and Vrije Universiteit Brussel) , Juan García-ruiz (LEC, IACT, CSIC, Universidad de Granada) , Liane G. Benning (GFZ German Research Centre for Geosciences; Free University of Berlin; University of Leeds) , Alexander E. S. Van Driessche (LEC, IACT, CSIC, Universidad de Granada; University Grenoble-Alpes)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Minerals , VOL 7

State: Published (Approved)
Published: August 2017
Diamond Proposal Number(s): 7893

Open Access Open Access

Abstract: Synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) was used to examine in situ the precipitation of gypsum (CaSO4·2H2O) from solution. We determined the role of (I) supersaturation, (II) temperature and (III) additives (Mg2+ and citric acid) on the precipitation mechanism and rate of gypsum. Detailed analysis of the SAXS data showed that for all tested supersaturations and temperatures the same nucleation pathway was maintained, i.e., formation of primary particles that aggregate and transform/re-organize into gypsum. In the presence of Mg2+ more primary particle are formed compared to the pure experiment, but the onset of their transformation/reorganization was slowed down. Citrate reduces the formation of primary particles resulting in a longer induction time of gypsum formation. Based on the WAXS data we determined that the precipitation rate of gypsum increased 5-fold from 4 to 40 °C, which results in an effective activation energy of ~30 kJ·mol−1. Mg2+ reduces the precipitation rate of gypsum by more than half, most likely by blocking the attachment sites of the growth units, while citric acid only weakly hampers the growth of gypsum by lowering the effective supersaturation. In short, our results show that the nucleation mechanism is independent of the solution conditions and that Mg2+ and citric acid influence differently the nucleation pathway and growth kinetics of gypsum. These insights are key for further improving our ability to control the crystallization process of calcium sulphate.

Journal Keywords: nucleation; multistep pathway; crystal growth; gypsum; additives

Subject Areas: Earth Science, Chemistry

Instruments: I22-Small angle scattering & Diffraction


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