In this study, phosphogypsum (PG) is simulated by doping fluorine and phosphorus ions in an analytically pure reagent of gypsum dihydrate. The influence of fluorine and phosphorus impurity and content on the dehydration reaction process of phosphogypsum and its crystalline micromorphology is assessed during the preparation …
the high-energy gypsum band, its appearance dur- ing dehydration can initially only be inferred from the smaller intensity decrease of the high-energy UOH.gypsum band compared to the low-energy VoH_ gypsum band. Spectra 2b-2d may be interpreted as a phase mixture of gypsum+hemihydrate,
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 …
Depending on the mill temperature, the gypsum becomes partially or completely dehydrated to hemihydrate or anhydrite respectively. According to [8] the temperatures at which gypsum dehydration to hemihydrate can take place lie between 95 and 170 °C. The results of [9] indicate that gypsum dehydration can even begin at temperatures …
OIG also known as Oman Gypsum Company is a leading Gypsum mining company based in Salalah, Oman. Gypsum found at our locations is of the finest quality and purity …
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 ...
Researchers, therefore, are constantly searching for new environmentally friendly stabilization methods to improve the engineering properties of soils. One …
A readily monitored and controllable hydrothermal system for the facile, cost-effective transformation of FGD gypsum to calcium sulfate hemihydrate whiskers. Particuology, 54 (2021), pp. 173-180. ... Dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite γ-CaSO 4. ACS Omega, 4 (4) (2019), pp. …
The first describes the process of water leaving the structure of gypsum to form hemihydrate or anhydrite. The second depicts the temperature-dependent …
The control of crystal morphology is crucial to preparation of α-hemihydrate gypsum (α-HH). α-HH was prepared from phosphogypsum (PG) in Na 2 SO 4 solution at different temperatures. The effect of maleic acid (C 4 H 4 O 4) on the dehydration rate and growth behavior of α-HH was investigated by X-ray diffraction (XRD) and scanning …
consumption of hemihydrate and formation of dihydrate. 1. Ultrasonic results indicate gypsum hydration reaction consists of two stages: the dissolution of hemihydrate in the first stage and the nucleation and precipitation of dihydrate in the second stage. 2. Gypsum hydration is strongly influenced by water amount. Spread flow test is
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 …
Partial Dehydration: When gypsum is partially dehydrated, it forms a material known as "plaster of Paris" or "calcined gypsum." Plaster of Paris is a white, powdery substance that can be mixed with water to create a workable plaster paste, used in various construction and artistic applications. ... Oman, and Saudi Arabia. Desert ...
during dehydration. In particular, Popp and Kern [1993] observed dramatic decreases in V P, V S and Poisson's ratio during experimental dehydration of lizardite and gypsum. [3] Two challenging problems encountered in addressing the possible importance of dehydration embrittlement in 1Laboratoire de Géologie, École Normale Supérieure, …
The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy and synchrotron X-ray diffraction with an externally heated diamond anvil cell. At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely …
GMC is one of largest manufacturer of Gypsum in GCC sourcing most of raw materials from Oman itself. GMC also engages in production of Limestone, Marbles.
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 …
Soil samples were distilled in two steps: first at 35°C and then at 130°C to separate free and gypsum crystallisation water while ensuring an almost complete dehydration of gypsum (Freyer and...
From stoichiometric considerations, dehydration of the dihydrate is expected to give a total mass loss of 20.9%, made up of steps of 15.7% (dihydrate → hemihydrate) and 5.2% (hemihydrate → anhydrous form, based on the mass of the dihydrate). The dehydration of the hemihydrate is expected to give a mass loss of 6.2%.
The band 3600 cm −1 in hemihydrate is lowered to 3540 cm −1 in gypsum, and the band 3550 cm −1 in hemihydrate to 3400 cm −1 indicates the hydrogen bonding. Hemihydrate contains only one type of water molecule attached to the anion, SO 4 2−, by hydrogen bonding but gypsum contains two types of water molecules out of which one …
Event/ Capillary environment Open+N2 Open Sealed Sealed + H2O 149 180 200 360 151.5 177 184 375 162.5 208 216 330 166 242 251 291 50% gypsum 50% hemihydrate Inception of major structural change in hemihydrate Formation of g-anhydrite 50% g-anhydrite 50% anhydrite Effect of heating rate on the dehydration of pure gypsum The …
A 'zero-water hemihydrate' is observed before refinement in the higher symmetry γ-anhydrite cell is possible. The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum …
Negro and Stafferi17,18studied the dehydration of gypsum and hemihydrate. Thegypsum dehydration was nucleation controlled and was modelled using 2d Avrami-Erofe'ev expression. The hemi-hydrate dehydration was expressed as a reaction with anorder of 0.68. Strydom et al.19 studied the dehydration byDTA using up …
It is found that the dehydration of gypsum to anhydrite proceeds via the hemihydrate and γ-anhydrite phases and the interplay and behaviour of these phases …
We report on changes in rock permeability induced by devolatilization reactions using gypsum as a reference analog material. Cylindrical samples of natural alabaster were dehydrated in air (dry) for up to 800 h at ambient pressure and temperatures between 378 and 423 K. Subsequently, the reaction kinetics, so induced …
Plaster, made of calcium sulfate hemihydrate (CaSO 4 •½H 2 O) and/or γ-anhydrite (CaSO 4) is obtained by dehydration of gypsum (CaSO 4 ·2H 2 O) at 100–200 °C. When mixed with water, it dissolves while new gypsum crystals precipitate. Plaster's microstructures affect its reactivity and setting properties, but are poorly understood due …
The dehydration process proceeds stepwise and leads to metastable calcium sulfate phases. Bassanite (calcium sulfate hemihydrate, CaSO 4 ·0.5 H 2 O) is formed at the loss of 1.5 mol H 2 O per formula unit with respect to gypsum. Hemihydrate exists in different morphologic forms (α, β and β′).
The effects of salt solution recycling on the transition of α-HH from FGD gypsum were investigated by a comparison with that in laboratory scale, focusing on the dehydration rate of FGD gypsum, the crystal morphology, chemical composition and mechanical strength of the products. α-HH could be transformed from FGD gypsum in …
This article addresses the thermal properties and the microstructure of gypsum boards produced from β-hemihydrate by studying its dehydration process. Dehydration reaction of gypsum boards was investigated from both micro and macro levels, employing thermogravimetric analysis and a ventilated oven. A new dehydration …
This subhydrate material is mixed with water at a construction site to form dihydrate (gypsum) again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated in several studies; the given references will give an overview of the research conducted up to now [3–15].