Crystallization Routes and Metastability of α-Calcium Sulfate Hemihydrate in Potassium Chloride Solutions under Atmospheric Pressure

Guan, Baohong; Ma, Xiaoyu; Wu, Zhongbiao; Yang, Lei; Shen, Zheqi

doi:10.1021/je8003222

Cited by 34 publications

(33 citation statements)

References 15 publications

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“…Despite its weaker intensity in comparison to that of the commercial product the characteristic exothermic peak in the DSC trace that distinguishes the alpha and beta HH varieties [40][41][42] can be clearly seen. In typical batch reactor growth rate studies, the change in solute concentration is used to derive the growth rate.…”

Section: Nearly Constant Supersaturation Crystallization Of α-Hhmentioning

confidence: 94%

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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Section: Nearly Constant Supersaturation Crystallization Of α-Hhmentioning

confidence: 94%

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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“…[1][2][3][4], showing excellent thermal stability and mechanical strength [5][6][7]. Calcium sulfate whiskers can be produced by preparing α-CaSO 4 ·0.5H 2 O whiskers through hydrothermal, acidification, reverse micro-emulsion, and microwave-assisted approaches [8][9][10][11][12][13] followed by calcination of the α-CaSO 4 ·0.5H 2 O whiskers above 600 • C [14,15]. Compared with the other methods, the hydrothermal route was widely used thanks to its moderate conditions and easily controlled parameters and whisker properties [16].…”

Section: Introductionmentioning

confidence: 99%

Influence of Alkyl Trimethyl Ammonium Bromides on Hydrothermal Formation of α-CaSO4·0.5H2O Whiskers with High Aspect Ratios

et al. 2017

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Abstract:In this paper, the influence of alkyl trimethyl ammonium bromides (C n H 2n+1 (CH 3 ) 3 NBr, n = 10, 12, 14, 16, 18, abbreviated as ATAB) on the formation of alpha calcium sulfate hemihydrate (α-CaSO 4 ·0.5H 2 O) whiskers under a hydrothermal condition (135 • C, 3.0 h) was analyzed. Specifically, it focuses on cetyl trimethyl ammonium bromide (C 16 H 33 (CH 3 ) 3 NBr, abbreviated as CTAB). The rising CTAB concentration from 0 to 9.2 × 10 −4 mol·L −1 led to the increase of the average aspect ratio of α-CaSO 4 ·0.5H 2 O whiskers from 80 to 430, since the selective adsorption of CTAB on the negatively-charged side facets of the whiskers inhibited the growth of the whiskers along the direction normal to the lateral facets. The further increase of CTAB concentration above the critical micelle concentration (abbreviated as CMC) showed little effect on the morphology of α-CaSO 4 ·0.5H 2 O whiskers, considering that CTAB tended to form micelles instead of being adsorbed on the whisker surfaces. Similar phenomena were observed in other ATABs (n = 10, 12, 14, 18).

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“…It has been revealed that HH crystal consists of corner-sharing SO 4 − and CaO 8 − polyhedral chains, which are hexagonally arranged and form a three-dimensional framework with continuous channels parallel to [001] direction. These channels have a diameter of about 4.5 Å and are partially filled with H 2 O molecules [10] .…”

Section: Morphologies Of the Surface Of α-Hh Crystalsmentioning

confidence: 99%

“…FGD gypsum thereby produced can amount up to 20 million tons per year since 2007. Besides utilizing FGD gypsum in wallboards and concrete blocks manufacturing, or in cement as an additive [3] , preparation of α-HH is one of the promising ways for FGD gypsum utilization, because this high value cementitious material has wide application areas for its superior workability and high strength [4,5] .…”

Section: Introductionmentioning

confidence: 99%

Characterization and precipitation mechanism of α-calcium sulfate hemihydrate growing out of FGD gypsum in salt solution

Yang

Guan

2009

Sci. China Ser. E-Technol. Sci.

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Alpha-calcium sulfate hemihydrate (α-HH) has been prepared from flue gas desulfurization (FGD) gypsum with salt solution method under atmospheric pressure. X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), optical micrograph, X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS), and scanning electron microscopy (SEM) have been employed to characterize the α-HH crystals, based on which the formation and growth mechanisms of the α-HH crystals have been discussed. The results show that FGD gypsum can be successfully transformed into high purity α-HH in salt solution under mild conditions, and that a dissolution-recrystallization route is most probably adopted by this transition. The growth of α-HH crystals in salt solution demonstrates a preferred direction along [001] and results in a bundle-of-sheets or bundle-of-raphide texture. The characteristics revealed in this study can help to understand and control the growth of the α-HH crystal from solution.FGD gypsum, calcium sulfate hemihydrate, dissolution-recrystallization, salt solution method

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Crystallization Routes and Metastability of α-Calcium Sulfate Hemihydrate in Potassium Chloride Solutions under Atmospheric Pressure

Cited by 34 publications

References 15 publications

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

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

Influence of Alkyl Trimethyl Ammonium Bromides on Hydrothermal Formation of α-CaSO4·0.5H2O Whiskers with High Aspect Ratios

Characterization and precipitation mechanism of α-calcium sulfate hemihydrate growing out of FGD gypsum in salt solution

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