Direct production of high-strength α-calcium sulfate hemihydrate (α-HH) with no additives was accomplished by the reaction of aluminum sulfate and waste CaCl 2 discarded from Solvay soda plant. For scaling-up this new process, the crystallization kinetics of α-HH was experimentally investigated under varying conditions including …

This article addresses the microstructure and related mechanical properties of gypsum produced from β-hemihydrate using information of its hydration process, from …

The Influences of soluble phosphorus on hydration process and mechanical properties of hemihydrate gypsum under deep retarding condition. Materials 15 (7), 2680 (2022).

Moulding gypsums are products made of calcium sulphate hemihydrate with optional factory additives, where very pure brilliant raw gypsum is used in their manufacture. Physically different hemihydrates are produced depending on the calcination process used: Alpha hemihydrate in the autoclave, or beta hemihydrate in the boiler plant or in the ...

Dihydrate and β-hemihydrate gypsum exhibit relatively higher solubility and dissolve more quickly than CaSO 4. However, there is little information on their incorporation in CAC. ... Heat evolution from the beginning of the process when water was mixed was monitored. Data was logged for 3 days and these results were used to …

Another way is a recrystallization process at around 100 °C in an autoclave filled with gypsum slurry. In this process, larger hemihydrate crystals can grow with …

Using solar energy to dehydrate gypsum to produce β-hemihydrate is one way to improve the carbon footprint 13,14 . Alternatively, α-hemihydrate is produced from gypsum using an autoclave process ...

Phosphogypsum (PG) is a kind of industrial solid waste with high impurity content and low utilization rate. In this study, α-hemihydrate gypsum (α-HH) was synthesized from PG in H 3 PO 4 –H 2 O solution (wet-process phosphoric acid solution and phosphoric acid solution) under atmospheric pressure. The crystal morphology of α …

The dehydration of gypsum (Gy) was studied, at negligible water vapor pressure, by in situ IR spectroscopy and by thermogravimetry to det. whether intermediate phases (CaSO4.nH2O) exist, other than the hemihydrate with n = 0.5, and also to compare the mechanism of the dehydration process when measured by 2 techniques with very …

For example, calcium phosphate from the hydration of soluble phosphorus can be absorbed on the surface of hemihydrate gypsum crystal which delays its hydration process and reduces strength [21, 22 ...

Upon heating, gypsum gradually loses its water, transforming into the hemihydrate, also known as bassanite, (CaSO 4 ·0.5H 2 0) and anhydrite (CaSO 4 ). …

Flue-gas desulphurization (FGD) gypsum is a highly prevalent industrial by-product worldwide, which can be an excellent alternative to natural gypsum due to its high content of CaSO4·2H2O. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved …

To obtain α-hemihydrate from gypsum-bearing wastes, the salt solution method is often considered [19][20][21][22][23][24][25]. In this case, dehydration is carried out in a solution of salts (Na ...

The hydration process of the β-hemihydrate was investigated applying an ultrasonic wave method and the influence of the water content on hydration was analyzed. ... In this study, a high-value-added recycled α-hemihydrate gypsum (α-RHG) generated from WGP using the atmospheric pressure hydrothermal method (APHM) was utilized to …

Efficient extraction of impurities from phosphogypsum during crystal regulation of α-hemihydrate gypsum. Qingjun Guan, Corresponding Author. ... (H 3 PO 4) with less similarity to SO 4 2−, which prevented the recombination of the released P with gypsum during the crystallization process. Furthermore, α-HH morphology and size …

The hydration mechanism of hemihydrate was proved to be dissolution and precipitation via in-situ ESEM observation.. The detailed dissolution process of hemihydrates were revealed: surface dissolution and particle fragmentation.. Gypsum precipitates at the beginning, crystallizes rapidly after 20 min hydration and tends to be …

The first describes the process of water leaving the structure of gypsum to form hemihydrate or anhydrite. The second depicts the temperature-dependent …

Preparation of α-hemihydrate gypsum crystal is an approach for utilization of phosphogypsum (PG), but the soluble phosphorus impurities in PG have a crucial …

The stockpiling of phosphogypsum (PG) poses a substantial risk of environmental pollution.To reduce the stockpile of PG and enhance its value, this research utilized phosphogypsum to produce α-hemihydrate gypsum (a-HH).The study elucidates the crystallization process of α-HH, which involves Ca 2+ helical growth and …

The deposition prevents further dissolution of hemihydrate gypsum ... To analyze the hydration process of hemihydrate with different concentrations of soluble P2O5, ...

Hemihydrate Kelley, Southard and Anderson' have shown that the thermodynamic properties of calcium sulphate hemihydrate depend on whether the ... facture of gypsum plaster by the kettle process) is

Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the attachment water of the mixture of FGD gypsum ...

A brand new method to transform flue gas desulfurization gypsum (FGD gypsum) into α-calcium sulfate hemihydrate (α-HH) with short hexagonal prisms …

hemihydrate gypsum, and the influence degree of different forms of soluble phosphorus is unclear. Therefore, the utilization of a-hemihydrate gypsum is greatly limited. In this study, the effect of soluble phosphorus on the setting time and mechanical properties of a-hemihydrate gypsum was investi-gated by adding different amounts of H 3PO 4 ...

Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. This dehydration process is technically performed in three different ways.

The main component of gypsum is calcium sulfate, and gypsum can be classified as anhydrite (CaSO 4), hemihydrate (CaSO 4 •0.5H 2 O, HH) and dihydrate gypsum …

An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl …

When gypsum is heated at about 150–160 °C, it loses approximately three-quarters of its water in a partial dehydration process and becomes hemihydrate gypsum (CaSO 4 •½H 2 O) or calcined gypsum; it is also known as beta gypsum (alpha gypsum is made by processing batches of gypsum under elevated pressure). Calcined gypsum or …

α-Calcium sulfate hemihydrate (α-HH) is an important cementitious material, which can be prepared by hydrothermal method from calcium sulfate dihydrate (DH) in an electrolyte solution. Study of the conversion kinetics of DH to α-HH in NaCl solution is helpful for understanding the control process. In this paper, X-ray diffraction (XRD) …

The Prayon HDH Process is a clever technology that maximizes the P₂O₅ strength in the acid and produces a high-quality gypsum. It consists of an attack of the phosphate rock under hemihydrate conditions. Hemihydrate slurry is filtered on a Prayon tilting pan filter to recover the phosphoric acid.