— The results show that the dehydration of PG to β-hemihydrate gypsum depends on calcination temperature and time. ... With the best calcination temperature of 800 °C, gypsum plaster showed a ...
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— The dehydration of PG to β-hemihydrate gypsum depends on the calcination temperature and time, and an increase in the calcination temperature is beneficial to …
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— Insights into the Role of Na + on the Transformation of Gypsum into α-Hemihydrate Whiskers in Alcohol–Water Systems. ..., and heated by circulating oil in the jacket. The temperature of the stock solution was monitored with a thermometer. ... Crystal water contents of the solids were determined by the mass loss during calcination at …
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Preparation of α-calcium sulfate hemihydrate from industrial by-product gypsum: a review Qingjun Guan 1, ... β-HH can be obtained by calcination of gypsum (Christensen et al., 2010; Schmidt et al., 2011). 170 Physicochem. Probl. Miner. ... elevated temperature (above 100 °C) and pressures, is energy-intensive (Ling and Demopoulos, 2005). ...
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DOI: 10.1016/j.cscm.2023.e02259 Corpus ID: 259291550; Influence of calcination and GGBS addition in preparing β-hemihydrate synthetic gypsum from phosphogypsum @article{Zhang2023InfluenceOC, title={Influence of calcination and GGBS addition in preparing $beta$-hemihydrate synthetic gypsum from phosphogypsum}, …
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— The rate of the gypsum-hemihydrate transformation is dominantly controlled by temperature, T, and the water vapour pressure in the reaction environment, p H2O [16] [17][18] . A temperature ...
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Gypsum precipitates from aqueous solution under ambient conditions, where it is the thermodynamically stable phase of calcium sulfate at temperatures below 40-60°C. 1, 2, 11,12 Anhydrite becomes ...
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The calcination is controlled by a thermocouple within the stucco bed that changes the feed to maintain a constant temperature, just like a full sized industrial calciner. Calcination temperature can be set at approximately 135-180℃ and can be tuned to minimize residual gypsum and soluble anhydrite production and maximize hemihydrate production.
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— The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination …
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— The rate of the gypsum-hemihydrate transformation is dominantly controlled by temperature, T, and the water vapour pressure in the reaction environment, p H2O 16,17,18.
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— Flue gas desulfurized gypsum mainly comes from thermal power plants, smelters, and large-enterprise boilers, and contains industrial by-products produced through a wet desulfurization combustion process, where SO 2 gas and lime slurry react under strong oxidation conditions. The main component of this gypsum is calcium sulfate …
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— In this study, the effect of sulphonated naphthalene formaldehyde condensate (SNF) and polycarboxylate (PC) superplasticizers on the performance of β-calcium sulphate hemihydrate plaster has been discussed. A considerable improvement in the properties of β-hemihydrate plaster was observed with an increase in …
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The preparation of natural and synthetic gypsum prior to calcination, such as drying and grinding. The various calcination methods for β-hemihydrate and α-hemihydrate are reviewed, such as batch kettle, continuous kettle, submerged combustion kettle, conical kettle, and other calcination equipment.
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— The synthesis of α-calcium sulfate hemihydrate (α-CSH) from flue gas desulfurization (FGD) gypsum is a good way to realize the comprehensive utilization of FGD gypsum. To obtain α-CSH with the satisfactory performances, a facile hydrothermal-aging pretreatment process for FGD gypsum raw materials was proposed, where FGD …
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— The α-hemihydrate hydration results in a high dihydrate formation; therefore, this type of gypsum is applied in conditions where more significant strengths are necessary (e.g. sculptures and sanitaryware casing) [36], [37]. β-Hemihydrate is obtained through the dry calcination of gypsum in the range of 120 °C–180 °C and it is an easier ...
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— Li and Zhang [21] investigated the dehydration behavior and impurity changes of PG at 120°C, concluding that PG could be converted into β-hemihydrate gypsum at this temperature, but the morphology of calcined gypsum became rough and many cracks formed, founding the impurity content did not decrease significantly and the eutectic …
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— The aim of the study was to evaluate the effect of the calcination temperature of synthetic gypsum binder on the binding properties of innovative gypsum pastes, as well as on the properties of …
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Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in …
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The plaster of Paris is prepared from gypsum (calcium sulfate dihydrate (CSD): CaSO 4 ⋅ 2H 2 O) which is mined from the earth or synthesized. When heated at about 160 °C, gypsum is converted in its hemihydrate form (CSH) which is used in plaster of Paris. The chemical reaction responsible for the setting and hardening of calcium sulfate ...
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— The temperature was monitored by a thermocouple and maintained within ± 0.5 °C. Then, 100 g of PG was added into the mixed solutions, and the slurry was stirred by a Teflon impeller at 250 r/min. ... Promotion of conversion activity of flue gas desulfurization gypsum into α-hemihydrate gypsum by calcination-hydration treatment. J. Cent ...
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volume ratio of hemihydrate/free water (0.36 for α- and 0.38 for β-hemihydrate), vn/vw the specific volume ratio of crystal water/free water (0.81 for α- and 0.71 for β-hemihydrate), w the water/hemihydrate ratio, and w0 the water requirement for the hydration reaction (0.186 for both α- and β-hemihydrate).
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— Two mechanisms of the dehydration of the gypsum, which main component of PG-O, were identified. It dehydrated into β-hemihydrate and III-anhydrate under low temperature calcination, while dehydrated into two kinds of anhydrite with different solubility and activity under high temperature calcination.
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When the gypsum is heated in a controlled environment, it partially loses its water of crystalization and converts into plaster or stucco is called Calcinated Gypsum. Heating of Gypsum: When the water of crystallization is removed from Gypsum (CaSO 4. 2 H 2 O), a Hemihydrate Gypsum or Calcined Gypsum (CaSO 4. 1 2 H 2 O) is produced.
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— After stirring for 40 min at a rate and temperature of 260 ... cost-effective transformation of FGD gypsum to calcium sulfate hemihydrate whiskers. Particuology, 54 (2021), pp. 173-180. View PDF View article View in Scopus Google Scholar. Chen et al., 2017. R. Chen, S. Hou, J. Wang, L. Xiang.
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— The results revealed smaller mass loss of high-temperature calcined gypsum products during dry-wet cycles between 50°C and 70°C, indicating superior waterproofing capabilities. ... It should be noted that without sulfuric acid addition, the predominant phase of calcined gypsum is hemihydrate and anhydrite just accounts for only a small ...
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— The marked points were observed after adjusting temperature and pressure for a while and then repeat the adjustment and observation until hydration is completed. ... the physical and mechanical properties of hemihydrate meet the requirements of level 2 in Chinese standard"calcined gypsum ... it is proved that the hydration of hemihydrate to ...
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— Dihydrate gypsum is the dominant phase composition in PG, it is a stable phase at room temperature but can be converted into α-hemihydrate gypsum (α-CaSO 4 ·0.5H 2 O) [16] and β-hemihydrate gypsum (β-CaSO 4 ·0.5H 2 O), also called building gypsum [17] according to different heating methods. α-hemihydrate gypsum is prepared …
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— Currently, a large number of studies have reported that FGD gypsum can be converted into hemihydrate gypsum (CaSO 4 ·0.5H 2 O, HH) to broaden its reuse. ... meeting the grade 1.6 requirements of building gypsum. The calcination temperature rises to 180 °C, 2 h flexural and compressive strength are respectively up to 2.6 and 4.3 MPa ...
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— The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite was also studied by Monte Carlo (MC) simulations. The thermodynamic calculation results reveal that the dehydration mechanism of gypsum …
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— Gypsum (calcium sulphate dihydrate) is of great industrial importance with over 95,000 ktonnes being used in the world per annum. The greatest use of gypsum is in the production of plaster (calcium sulphate hemihydrate) for use as an interior finisher. Plaster is produced by the calcination (thermal decomposition) of gypsum. The most …
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— The results show that the obtained hemihydrate gypsum mixing with water can prepare high-performance building gypsum after the FGD gypsum adding 3–5 wt% …
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temperatures than those for the mechanical mixture (curve b), this may indicate slight differences between different preparations of both oc- and ~-hemihydrates.
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— Figure 1 represents the cycling mechanism of gypsum, starting from hemihydrate. In the first stage, the hydration reaction will take place immediately after hemihydrate addition to water. ... (Toni Technik Baustoffprüfsysteme -Germany) using (1 : 1) water to solid ratio. The measurement time and temperature were fixed at …
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— Here we report a facile and cost-effective wet-chemical approach to the synthesis of calcium sulfate hemihydrate nanowires (HH NWs, CaSO4·0.5H2O), and their robust performance in immobilizing water molecules to the crystal lattice of CaSO4 and then separating them from a surfactant-stabilized water-in-oil emulsion (mean droplet size of …
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— 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. …
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— The mineralogical composition, microstructure, and reactivity of traditional gypsum, a multiphase product, is closely connected to its calcination temperature, but systematic studies which relate ...
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