It can be assumed that if the dehydration process also happens inside the deeper layers of the gypsum crystal, it should be possible to form conditions like in a …
DOI: 10.1016/J.FUEL.2009.01.004 Corpus ID: 98555701; Preparation of α-calcium sulfate hemihydrate from FGD gypsum in K, Mg-containing concentrated CaCl2 solution under mild conditions
Mentioning: 42 - Flue gas gypsum may be converted to a-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 a-hemihydrate gypsum and, thus, its quality …
Under optimal working conditions the quality of the formed α-hemihydrate gypsum is similar to that of a material produced in an autoclave. References. 1 E. Eipeltauer, " Preparation of Crude Gipseous Rock and Its Conversion into Its Various Hemihydrate Plaster Forms " (in Ger.), Zem.–Kalk–Gips, 11, 264, 304 ( 1958 ).
To enable further work to be carried out on the hydration of hemihydrate plasters, materials purer than the available commercial plasters and with reproducible properties were required. As a first stage in the attempted preparation of such materials, the process variables in the autoclave dehydration of gypsum were investigated. Methods …
The chemical composition of alpha hemihydrate (α-HH) from the steam autoclave process and beta hemihydrate (β-HH) were determined by XRD as shown in Table 1. In more detail, hemihydrate was added to water to perform the hydration reaction to obtain dihydrate, and then, the formed dihydrate was crushed and calcinated back to …
Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO4·2H2O), hemihydrate (CaSO4·0.5H2O) and anhydrite (CaSO4).
For the first time, α-calcium sulfate hemihydrate (α-HH) was successfully prepared from calcium sulfate dihydrate (DH) in methanol–water solution under atmospheric pressure. The effect of methanol concentrations (40–73 mol%) on the transition from DH to α-HH were investigated at temperatures (60°–75°C) within a reaction time of 36 h. The results …
A high-quality alpha hemihydrate based on natural gypsum with a very fine grinding. Due to the fine grinding and its excellent strength, Spezial 40 is ideal as a base gypsum for use in high-quality building products. ... Raddichem 27 is produced in suspension autoclaves and is characterised by its particularly high purity and uniformity ...
This method has been used only at the industrial level. The first industries for the autoclave production of alpha–hemihydrate by this method were built in Germany (Guilini) in 1962 and Japan (Nitto) in 1973 [1 – 4]. ... Forester J.: Chem. Ing. Tech. 44, 969 (1972). Krueger B.: Process for Producing α–Hemihydrate Gypsum Crystals from ...
The process of converting gypsum into alpha hemihydrate involves heating gypsum at a specific temperature to remove water molecules, resulting in a more concentrated and stable form of calcium sulfate. The term "alpha" in alpha hemihydrate refers to the unique crystal structure formed during this dehydration process. The alpha …
use of autoclaves and crystal modifiersto convert the crystal structure, one is the SICOWA-ProMineral process, 9 in which stable stackable blocks made from finelydivided FGD gypsum
Phosphogypsum (PG), as a waste by-product with high content and complicated impurities, is difficult to be utilised effectively. Herein, cleaner PG is prepared with "HCl H 2 SO 4 method", and thus is used to synthesise α-hemihydrate gypsum (α-HH) in CaCl 2 solution under atmospheric pressure. Morphology and mechanical …
Semantic Scholar extracted view of "Autoclave-Free Formation of α-Hemihydrate Gypsum." by A. Zuerz et al. Skip to search form Skip to main content Skip to ..., title={Autoclave-Free Formation of $alpha$-Hemihydrate Gypsum.}, author={A. Zuerz and Ivan Odler and Felicia Thiemann and Katarina Bergh{"o}fer}, …
Several fabrication approaches are commonly adopted to prepare the a-CSH, including autoclave heating and chemical synthesize methods etc. 4,5,[18][19][20][21] Among them, autoclave heating is one ...
This study was performed to investigate the formation process of calcium sulfate α-hemihydrate from FGD gypsum produced at thermal power plant burning bituminous coal. The experimental results showed that calcium sulfate α-hemihydrate with a large aspect ratio was produced in the temperature range of 120 °C and 140 °C in the absence of …
To enable further work to be carried out on the hydration of hemihydrate plasters, materials purer than the available commercial plasters and with reproducible properties were required. As a first stage in the attempted preparation of such materials, the process variables in the autoclave dehydration of gypsum were investigated.
The progress of the gypsum to a-hemihydrate conversion was monitored by microscopic observation of the suspension. After completing the reaction the suspension was rapidly …
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 …
Analytical grade glycerol (C 3 H 8 O 3), sodium sulfate (Na 2 SO 4) and citric acid (C 6 H 8 O 7 ·H 2 O) were purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd., China. PG was collected from a phosphate fertilizer plant in Guizhou Province, China. The X-ray diffraction (XRD) (X'Pert PRO, PANalytical Company, Netherlands) …
It can be inferred that in the process of the HH-CSW formation from gypsum, two Ca–O–H bonds of gypsum was broken up and they formed two Ca–O–S bonds, as illustrated in Fig. 10. The formation of two Ca–O–S bonds along the a-axis resulted in the blocking of the H 2 O channel of the a-axis while that of the c-axis was …
The first describes the process of water leaving the structure of gypsum to form hemihydrate or anhydrite. The second depicts the temperature-dependent …
This study investigates the potential of α-HH formation from gypsum originating from activated and hydrated natural anhydrite. For this, gypsum was …
Similar results can be achieved by recrystallization from gypsum slurry around 100 °C in an autoclave or under a water steam atmosphere. However, in contrast, the recrystallization process here...
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) …
Alpha high‐strength hemihydrate gypsum (CaSO 4 ·0.5H 2 O, α‐HH) with a large‐size columnar crystal (average size: 135.31 µm, maximum size: 500 µm) is successfully prepared via a NaCl ...
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-HH was controlled by adding F and Al compound regulators, and the mechanical properties of α-HH were …
process at around 100 C in an autoclave filled with gypsum slurry. In this process, larger In this process, larger hemihydrate crystals can grow with fewer surface defects.
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 …
None of the experiments were performed in an autoclave; gypsum crystals were only heated in a furnace and the crystal seems to be acting as an autoclave. Through several experiments, it was clearly shown that the new-formed crystals inside of the gypsum crystal are alpha-hemihydrate and the experimental proof for Fowler et al. theory was ...
The α form material is also produced by heating gypsum, but this material is heated to 123 °C under approximately 1.2 kg/cm 2 (17 psi) of pressure, in steam for 5 to 7 hours in an autoclave. Processing gypsum in this way produces more dense crystals with little porosity, and these crystals require less water for setting and produce the dense ...
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Curing under steam atmosphere is a key process for the production of α-hemihydrate from raw gypsum stone. The α-hemihydrate is used to produce moulding plasters, gypsum building materials and special …
