Calcium Sulfate Precipitation Throughout Its Phase Diagram

Driessche, Alexander E. S. Van; Stawski, Tomasz M.; Benning, Liane G.; Kellermeier, Matthias

doi:10.1007/978-3-319-45669-0_12

Cited by 73 publications

(127 citation statements)

References 114 publications

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“…Furthermore, calcium sulphate minerals are among the most common scalants [3], causing serious reduction in the efficiency of for example desalination plants [4]. Due to their prominent role in both natural and industrial environments, the precipitation behaviour of CaSO 4 phases has been a much-studied topic (e.g., [5]). Until recently, the formation of gypsum from solution (the stable phase < 60 • C) was assumed to proceed via a single-step pathway (e.g., [6]).…”

Section: Introductionsupporting

confidence: 46%

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

et al. 2017

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Synchrotron-based small-and wide-angle X-ray scattering (SAXS/WAXS) was used to examine in situ the precipitation of gypsum (CaSO 4 ·2H 2 O) from solution. We determined the role of (I) supersaturation, (II) temperature and (III) additives (Mg 2+ 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 Mg 2+ 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 . Mg 2+ 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 Mg 2+ 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.

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Section: Introductionsupporting

confidence: 46%

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

et al. 2017

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“…Together with its hydrates, calcium sulfate is a very important mineral industrially, having a broad range of applications in fields as diverse as construction, medicine, cosmetics and ceramics (Tritschler et al, 2015). The CaSO 4 -H 2 O system has five crystalline phases (Van Driessche et al, 2017). Four exist at room temperature: calcium sulfate dihydrate, calcium sulfate hemihydrate, -anhydrite and -anhydrite.…”

Section: Introductionmentioning

confidence: 99%

A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate

Gurgul

Seng²,

Williams

2019

J Synchrotron Radiat

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The conversion of CaSO4·0.5H2O to CaSO4·2H2O is of great importance industrially, being the reaction behind plasterboard production and the setting of medical plasters. A detailed kinetic and mechanistic study of this process was conducted using time-resolved synchrotron X-ray diffraction in this work. The CaSO4·2H2O product is very similar regardless of whether the α- or β-form of CaSO4·0.5H2O is used as the starting material, but the reaction process is very different. The induction time is usually shorter for α-CaSO4·0.5H2O than β-CaSO4·0.5H2O, and a greater conversion percentage is observed with the former (although in neither case does the reaction proceed to 100% completion). The temperature of the system, widely used in industry as an indirect measure of the extent of the hydration process, is found to be a poor proxy for this, with the maximum temperature reached well before the reaction is complete. The Avrami–Erofe'ev and Gualtieri models could both be fitted to the experimental data, with the fits being substantially closer in the case of α-CaSO4·0.5H2O. The rate of reaction in the Avrami model tends to increase with the amount of gypsum seeds added to accelerate the process, and the importance of nucleation declines. The Gualtieri analysis suggested that the rate of nucleation increases substantially with the amount of seeds added, while there are less distinct changes in the rate of crystal growth. At low seed concentrations (<0.5% w/w) the rate of crystal growth is greater than the rate of nucleation, but at concentrations above 0.5% w/w nucleation is faster. These findings represent the first synchrotron study of the conversion of CaSO4·0.5H2O to CaSO4·2H2O, and will be of importance to gypsum producers globally.

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“…Phase transitions from less dense states to more dense ones are omnipresent in a wide spectrum of natural phenomena around us [1,2]. Examples can be found in cloud and polar cap formation [3][4][5], biomineralization processes such as bone development [6][7][8], protein aggregation and colloidal crystallization in living cells [9][10][11], and volcano and black hole formation [12,13]. These transitions are characterized by an initial incubatory stage governed by random density fluctuations that appear spontaneously in the mother phase (nucleation clusters).…”

Section: Introductionmentioning

confidence: 99%

General framework for nonclassical nucleation

et al. 2018

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A great deal of experimental evidence suggests that a wide spectrum of phase transitions occur in a multistage manner via the appearance and subsequent transformation of intermediate metastable states. Such multistage mechanisms cannot be explained within the realm of the classical nucleation framework. Hence, there is a strong need to develop new theoretical tools to explain the occurrence and nature of these ubiquitous intermediate phases. Here we outline a unified and self-consistent theoretical framework to describe both classical and nonclassical nucleation. Our framework provides a detailed explanation of the whole multistage nucleation pathway showing in particular that the pathway involves a single energy barrier and it passes through a dense phase, starting from a lowdensity initial phase, before reaching the final stable state. Moreover, we demonstrate that the kinetics of matter inside subcritical clusters favors the formation of nucleation clusters with an intermediate density, i.e. nucleation precursors. Remarkably, these nucleation precursors are not associated with a local minimum of the thermodynamic potential, as commonly assumed in previous phenomenological approaches. On the contrary, we find that they emerge due to the competition between thermodynamics and kinetics of cluster formation. Thus, the mechanism uncovered for the formation of intermediate phases can be used to explain recently reported experimental findings in crystallization: up to now such phases were assumed a consequence of some complex energy landscape with multiple energy minima. Using fundamental concepts from kinetics and thermodynamics, we provide a satisfactory explanation for the so-called nonclassical nucleation pathways observed in experiments.

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Calcium Sulfate Precipitation Throughout Its Phase Diagram

Cited by 73 publications

References 114 publications

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate

General framework for nonclassical nucleation

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