Phase transformation kinetics of calcium sulfate phases in strong CaCl2HCl solutions

Feldmann, Thomas; Demopoulos, George P.

doi:10.1016/j.hydromet.2012.08.015

Cited by 32 publications

(17 citation statements)

References 26 publications

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“…As can be seen, in all three crystallization experiments DH crystals were produced. In other words no phase transformations took place in the system at 40 °C under the solution compositions used in accordance with results discussed in a previous article …”

Section: Resultssupporting

confidence: 91%

“…Figure shows very good agreement between the DH reference pattern and the measured diffraction, and no formation of calcium sulfate HH was detected. As discussed previously HH crystals have an elongated shape and commonly form by phase transformation from DH . However, this was not observed so no phase transformation took place.…”

Section: Resultsmentioning

confidence: 72%

“…In other words no phase transformations took place in the system at 40 • C under the solution compositions used in accordance with results discussed in a previous article. 40 Figure 3 shows the morphology of DH produced under the three different crystallization regimes investigated. There appears a distinct difference in crystal morphology between DH nucleated under mild (dilute solution) condition ( Fig.…”

Section: Calcium Sulfate Dihydrate Crystal Morphology In the Absence mentioning

confidence: 99%

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Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl₂‐HCl solutions

Feldmann

Demopoulos

2013

J of Chemical Tech & Biotech

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BACKGROUND This work deals with the effect of several additives on the morphology of calcium sulfate dihydrate (DH) crystals, produced by reactive crystallization involving strong CaCl2–HCl solutions. Experiments were conducted at 40 °C under various conditions, namely homogeneous and seeded (heterogeneous) crystallization in CaCl2/HCl solutions ranging from very dilute (0.42 mol L−1/0.04 mol L−1) to very concentrated (1.8 mol L−1/6.3 mol L−1). RESULTS In the absence of additives a distinct difference in crystal morphology was observed depending on solution composition. Homogeneously formed DH crystals from dilute solution were in the form of needles. DH crystals formed in concentrated acid solution were thick elongated plates. The most influential additives in concentrated solutions were CTAB (cetyltrimethylammoniumbromide), PAA (polyacrylic acid) and PVS (polyvinyl sulfonic acid). CTAB favoured formation of industrially interesting thick slab crystals. In contrast PAA favoured the formation of elongated and thinner crystals as a result of preferential crystal plane adsorption. PVS had a detrimental effect on DH crystal nucleation and growth explained by its polymeric structure. CONCLUSION Apart from PVS, CTAB and PAA no influence was seen for the majority of additives tested. This was attributed to lack of ionization caused by the highly acidic solutions. © 2013 Society of Chemical Industry

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 72%

Section: Calcium Sulfate Dihydrate Crystal Morphology In the Absence mentioning

confidence: 99%

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Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl₂‐HCl solutions

Feldmann

Demopoulos

2013

J of Chemical Tech & Biotech

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“…It involves curing DH in various aqueous solutions of salts near the boiling point . The formation zone of α‐HH in salts solutions depends on the temperature and the water activity that is lowered by the salts . In this work, the metastability of α‐HH, especially its MLT, was studied.…”

Section: Introductionmentioning

confidence: 99%

“…21,22 The formation zone of a-HH in salts solutions depends on the temperature and the water activity that is lowered by the salts. 23 In this work, the metastability of a-HH, especially its MLT, was studied. Thermodynamic metastable window for a-HH preparation from DH in CaCl 2 solution was constructed as a function of CaCl 2 concentration and temperature.…”

Section: Introductionmentioning

confidence: 99%

Insight into Metastable Lifetime of α‐Calcium Sulfate Hemihydrate in CaCl₂ Solution

Jiang

Mao

et al. 2013

J. Am. Ceram. Soc.

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Alpha calcium sulfate hemihydrate (α‐HH), an important kind of cementitious material, is a metastable phase in CaSO4–H2O system. In CaCl2 solution, thermodynamic metastable window for α‐HH preparation from calcium sulfate dihydrate is constructed as a function of CaCl2 concentration (0–4.0m) and temperature (60°C–130°C), and then the metastability of α‐HH is characterized by the metastable lifetime (MLT). As the concentration of CaCl2 is raised from 1.5 to 4.0m and temperature from 80°C to 110°C, MLT of α‐HH decreases gradually from 2920 to 60 min. The reducing effect of CaCl2 on MLT arises from its contribution to lowering the total interfacial Gibbs free energy required for the subsequent phase transition of α‐HH to anhydrite, the thermodynamic stable phase. This work establishes a method to evaluate the phase metastability and provides a potential approach to optimize the reaction time in metastable material synthesis according to the MLT value for purity control.

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Hydrochloric Acid Regeneration via Calcium Sulfate Crystallization for Non‐Ferrous Chloride Leaching Processes

Feldmann¹,

Demopoulos²

2013

Ni–Co 2013

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Phase transformation kinetics of calcium sulfate phases in strong CaCl2HCl solutions

Cited by 32 publications

References 26 publications

Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl₂‐HCl solutions

Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl₂‐HCl solutions

Insight into Metastable Lifetime of α‐Calcium Sulfate Hemihydrate in CaCl₂ Solution

Hydrochloric Acid Regeneration via Calcium Sulfate Crystallization for Non‐Ferrous Chloride Leaching Processes

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Phase transformation kinetics of calcium sulfate phases in strong CaCl2HCl solutions

Cited by 32 publications

References 26 publications

Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl2‐HCl solutions

Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl2‐HCl solutions

Insight into Metastable Lifetime of α‐Calcium Sulfate Hemihydrate in CaCl2 Solution

Hydrochloric Acid Regeneration via Calcium Sulfate Crystallization for Non‐Ferrous Chloride Leaching Processes

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Product

Resources

About

Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl₂‐HCl solutions

Effects of crystal habit modifiers on the morphology of calcium sulfate dihydrate grown in strong CaCl₂‐HCl solutions

Insight into Metastable Lifetime of α‐Calcium Sulfate Hemihydrate in CaCl₂ Solution