Growth of gypsum

Witkamp, G.J.; Eerden, J.P. van der; Rosmalen, G.M. van

doi:10.1016/0022-0248(90)90912-5

Cited by 56 publications

(54 citation statements)

References 17 publications

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“…(II) The influence of temperature on the precipitation behavior was analyzed by conducting experiments at five temperatures (4,12,21,30,40 • C) for a 50 mmol·L −1 CaSO 4 solution. (III) Finally, the effect of additives on the precipitation of calcium sulphate was studied for 50, 75, 100 and 150 mmol·L −1 CaSO 4 solutions at 21 • C. One additive, Mg, which enhances the solubility of CaSO 4 , was introduced, replacing the Na + ions with Mg 2+ ions in stoichiometric conditions (MgSO 4 ·7H 2 O and CaCl 2 ·2H 2 O were used as reactants, and a 1:1 Ca 2+ /Mg 2+ ratio was maintained for all cases).…”

Section: Methodsmentioning

confidence: 99%

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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: Methodsmentioning

confidence: 99%

“…The second series of experiments probed the precipitation kinetics of a 50 mmol·L −1 CaSO 4 solution at five different temperatures (4,12,21,30, and 40 • C). Figure 3b shows the evolution of the normalized peak area as a function of the reaction time for the (020) reflection.…”

Section: The Effect Of Supersaturation and Temperature On The Crystalmentioning

confidence: 99%

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

et al. 2017

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“…In such cases, S during dissolution or precipitation may be empirically related to the initial total surface area (S o ) by (Christoffersen and Christoffersen, 1976;Witkamp et al, 1990;Zhang and Nancollas, 1992;He et al, 1994)…”

Section: Reactive Surface Areamentioning

confidence: 99%

“…P equals to 2/3 if the shape of the crystals remains unchanged and rates on all faces are equal. P values of 0.5 indicate that dissolution or growth occur predominantly in two directions while P values of 0 indicate one direction (e.g., Witkamp et al, 1990). The reactive surface areas may also vary during experiments as a result of the extinction of highly reactive fine particles (Helgeson et al, 1984), change of the ratios of reactive and nonreactive sites (Gautier et al, 2001), mechanical disaggregation of particles (Nagy and Lasaga, 1992;Ganor et al, 1999), and formation of surface coating (Ganor et al, 1995;Nugent et al, 1998;Cubillas et al, 2005;Metz et al, 2005).…”

Section: Reactive Surface Areamentioning

confidence: 99%

Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems: 4. Numerical modeling of kinetic reaction paths

Zhu

Lü

Zheng

et al. 2010

Geochimica et Cosmochimica Acta

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This paper explores how dissolution and precipitation reactions are coupled in batch reactor experimental systems at elevated temperatures. This is the fourth paper in our series of "Coupled Alkali Feldspar Dissolution and Secondary Mineral Precipitation in Batch Systems". In our third paper, we demonstrated via speciation-solubility modeling that partial equilibrium between secondary minerals and aqueous solutions was not attained in feldspar hydrolysis batch reactors at 90-300°C and that a strong coupling between dissolution and precipitation reactions follows as a consequence of the slower precipitation of secondary minerals ). Here, we develop this concept further by using numerical reaction path models to elucidate how the dissolution and precipitation reactions are coupled. Modeling results show that a quasi-steady state was reached. At the quasi-steady state, dissolution reactions proceeded at rates that are orders of magnitude slower than the rates measured at far from equilibrium. The quasi-steady state is determined by the relative rate constants, and strongly influenced by the function of Gibbs free energy of reaction (DG r ) in the rate laws.To explore the potential effects of fluid flow rates on the coupling of reactions, we extrapolate a batch system (Ganor et al., 2007) to open systems and simulated one-dimensional reactive mass transport for oligoclase dissolution and kaolinite precipitation in homogeneous porous media. Different steady states were achieved at different locations along the one-dimensional domain. The time-space distribution and saturation indices (SI) at the steady states were a function of flow rates for a given kinetic model. Regardless of the differences in SI, the ratio between oligoclase dissolution rates and kaolinite precipitation rates remained 1.626, as in the batch system case (Ganor et al., 2007). Therefore, our simulation results demonstrated coupling among dissolution, precipitation, and flow rates.Results reported in this communication lend support to our hypothesis that slow secondary mineral precipitation explains part of the well-known apparent discrepancy between lab measured and field estimated feldspar dissolution rates (Zhu et al., 2004). Here we show how the slow secondary mineral precipitation provides a regulator to explain why the systems are held close to equilibrium and show how the most often-quoted "near equilibrium" explanation for an apparent field-lab discrepancy can work quantitatively. The substantiated hypothesis now offers the promise of reconciling part of the apparent fieldlab discrepancy.

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“…In the past there have been numerous investigations of the growth kinetics of calcium sulfate dihydrate [24][25][26] observing a second order growth rate law but very few on α-calcium sulfate hemihydrate [27][28][29]. These studies mostly focused on dilute solutions or a different matrix than the CaCl 2 -HCl system investigated here.…”

Section: Introductionmentioning

confidence: 99%

The crystal growth kinetics of alpha calcium sulfate hemihydrate in concentrated CaCl2–HCl solutions

Feldmann

Demopoulos²

2012

Journal of Crystal Growth

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The crystal growth kinetics of calcium sulfate α-hemihydrate (α-HH) in nearly constant supersaturated HCl-CaCl 2 solutions were investigated. Two types of solutions were used, the first had a low HCl (1.4 mol/L) and high CaCl 2 (2.8 mol/L) concentration and the second had a high HCl (5.6 mol/L) and low CaCl 2 (0.7 mol/L) concentration. These conditions were chosen to represent the first and last stage of a newly developed stage-wise HCl regeneration process. The seeded growth experiments were carried out in a stirred, temperature controlled semi-batch reactor in which supersaturation was kept constant by simultaneous addition of CaCl 2 and Na 2 SO 4 solutions. The influence of the following parameters on α-HH crystal growth was studied: temperature (70-95°C), specific power input of stirring (0.02-1.29 W/kg) and equimolar inflow rate of CaCl 2 and Na 2 SO 4 (0-0.6 mol/h). The crystal growth rate was derived from particle size distribution measurements made with the laser light diffraction technique. It was found that the surface area normalized crystal growth rate increased linearly with the molar inflow rate up to 0.3 mol/h, at higher inflow rates no further increase of the growth rate was observed. Temperature and specific power input, within the investigated ranges, did not show a marked effect on the growth rate, attributable to a diffusion/adsorption controlled growth process. An interesting finding of the present research is the establishment of a positive relationship between the narrowing of the width of the particle size distribution with increasing crystal growth rate. The results show that the resulting particle size distribution is positively related to the reagent inflow rate, a finding that can be applied to the industrial design and scale-up of the α-HH crystallization/HCl regeneration process.

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Growth of gypsum

Cited by 56 publications

References 17 publications

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems: 4. Numerical modeling of kinetic reaction paths

The crystal growth kinetics of alpha calcium sulfate hemihydrate in concentrated CaCl2–HCl solutions

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