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 …
Research highlights Water demand of β-hemihydrate was determined using spread flow test, and the influence of water content on the flowability was analyzed. The deformation coefficient of the β-hemihydrate was derived, the thickness of a water layer around the particles to assure the fluidity of the hydrating system was discussed, and …
It is evident that hemihydrate gypsum containing Na 2 HPO 4 had a longer peak II than S4 (0.06 wt.% retarder), because the protein retarder mainly prolonged the initial setting time. Once, the initial setting was achieved, the gypsum hydration process was accelerated, which can indicated the rapid achievement of final setting .
The formation mechanism of HH-CSW from flue gas desulfurization (FGD) gypsum is discussed based on the analysis of gypsum structure.
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 …
In this paper, the dihydrate–hemihydrate recrystallization method was employed to produce β-hemihydrate gypsum. The effects of thermodynamic conditions such as temperature, sulfuric acid concentration, and phosphoric acid concentration on the removal of F and P impurities were investigated. Kinetic studies revealed that the …
DOI: 10.1016/J.CONBUILDMAT.2019.04.148 Corpus ID: 149815625; Preparation of α-hemihydrate gypsum from phosphogypsum in recycling CaCl2 solution @article{Wenda2019PreparationO, title={Preparation of $alpha$-hemihydrate gypsum from phosphogypsum in recycling CaCl2 solution}, author={Lu Wenda and Baoguo Ma …
The hydration of calcium sulphate hemihydrate (CaSO 4 ·0.5H 2 O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO 4 ·2H 2 O) has been the subject of several investigations over a long period and a vast amount of data is widely distributed throughout in the literature. In this review article an overall picture of the …
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 …
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 …
Hemihydrate gypsum is found in two forms: α-hemihydrate gypsum (α-CaSO 4 ⋅0.5H 2 O) and β-hemihydrate gypsum ... Nevertheless, the complex α-hemihydrate gypsum manufacturing process incurs high costs and limits its large-scale utilization [9]. Therefore, the recycling of PG into β-hemihydrate synthetic gypsum (SG) …
The calcium sulphate dihydrate gypsum (CaSO 4 ·2H 2 O) is the most common sulphate evaporite mineral on our planet 1.Sulphate evaporites play an important role in Earth's sulphur cycle and are ...
Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated.
This is a two-stage process with calcium sulphate hemihydrate formed in the first stage being transformed to dihydrate gypsum in the second stage prior to discharge as a by-product. The filter acid may be further concentrated by evaporation, if required, for downstream uses. 2. Basics of Hemihydrate (HH) Process 2.1.
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). …
Calcium Sulfate Hemihydrate, also known as plaster of Paris, is a material made from gypsum that has been used for centuries in construction and various medical applications, including bone repair and growth factor release. ... In contrast, if water is supplied during the setting process, the gypsum crystals can grow further. For absorption ...
A brand new method to transform flue gas desulfurization gypsum (FGD gypsum) into α-calcium sulfate hemihydrate (α-HH) with short hexagonal prisms …
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 …
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 ...
Semantic Scholar extracted view of "Preparation of alpha-calcium sulfate hemihydrate from FGD gypsum in chloride-free Ca(NO3)2 solution under mild conditions" by Guangming Jiang et al. ... (PG) is a by-product of the wet-process phosphoric acid process, which causes serious environmental issues. In this work, PG was taken as raw …
In recent years, the massive accumulation of industrial by-product gypsum, especially flue gas desulfurization (FGD) gypsum and phosphogypsum (PG), not only encroaches on lands but also causes serious environmental pollution. The preparation of α-calcium sulfate hemihydrate (α-HH) from industrial by-product gypsum is an important …
Semantic Scholar extracted view of "Utilization of phosphogypsum to synthesize α-hemihydrate gypsum in H3PO4–H2O solution" by Long Chen et al. ... Results show that the modified dispersive kinetic model is very important in describing the entire kinetic process, indicating that α- HH–DH hydration includes induction of …
There is a poor understanding of the effect of impurities in phosphate rock on the crystal habit of gypsum during wet-process phosphoric acid production. The present work studies the effects of Al3+, SiF62-, and F- on the habit of gypsum in an MSMPR crystallizer. It is found that the gypsum crystal shape changes little in the presence of …
Flue gas gypsum may be converted to α-hemihydrate by suspending the starting material in inorganic salt solutions of high concentration or in diluted sulfuric acid and maintaining the suspension at boiling, or near boiling temperature for a period of time. The crystal morphology of the produced α-hemihydrate gypsum and, thus, its quality …
When gypsum is heated, it undergoes a process called calcination, during which it loses some or all of its water content, depending on the temperature and duration of heating. ... Oman, and Saudi Arabia. Desert Environments: North Africa: Countries in North Africa, such as Morocco and Tunisia, have extensive gypsum deposits in arid desert …
The study by Schneider [11] on the effects of retarders focused on the configuration process for hemihydrate gypsum, using citric acid and tartaric acid as additives. In this case, mechanical ...
The hydration of calcium sulphate hemihydrate (CaSO 4 ·0.5H 2 O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO 4 ·2H 2 O) has …
The first describes the process of water leaving the structure of gypsum to form hemihydrate or anhydrite. The second depicts the temperature-dependent solubility of the calcium sulphates in water. The third illustrates the hydration energy of …
Transforming gypsum into α-calcium sulfate hemihydrate (α-HH) provides a promising utilization pathway for the abundant amount of chemical gypsum. ... Investigation of the transformation process at neutral pH revealed that the arsenate ions in solution were distributed into α-HH and generated an enrichment of arsenic by 4-6 times. Arsenate ...
The effects of phosphoric acid (H3PO4) in pressurized aqueous solution on the dehydration of CaSO4·2H2O to form α-hemihydrate gypsum (α-HH) phase and the …
