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The changes from gypsum to anhydrite and back to gypsum are common processes (Klimchouk, 2000). This way, James (1992) noted that in very hot climates gypsum can dehydrate to anhydrite when it is ...
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These new virial coefficients can also be used to predict the solubilities of gypsum and anhydrite accurately. ... more with temperature at larger pressures. When pressure increases from 1 bar to 1400 bar, the solubility of gypsum increases significantly. ... Slusher R (1966) Thermodynamics of calcium sulfate dihydrate in aqueous sodium ...
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This also explains that in the early stage of the hydration reaction, the hydration rate and hydration exothermic rate of K 2 CO 3 to fluorogypsum are higher than those of KHCO 3 [32, 59]. However ...
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The crystal structure of anhydrous phosphogypsum hydration product dihydrate gypsum after adding carbide slag alone was poor in the later stage, and the length-diameter ratio decreased. ... The difference was that the rate of increase of the bleeding rate as W/B increased in the interaction of CS and W/B was smaller in the case of larger dosage ...
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1. Introduction. Flue gas desulfurization (FGD) gypsum is an industrial by-products, which primarily consists of dihydrate gypsum (CaSO 4 ⋅2H 2 O),and the treatment of 1 t of SO 2 in coal flue gas by limestone-gypsum wet desulfurization technology will produce about 2.7 t of FGD gypsum, and China emitted nearly 100 million t of FGD gypsum by 2020 [1].At …
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Here, we report the first solid-like dehydration of gypsum to produce anhydrite at room temperature. Specifically, a 39 nm thick sulfuric acid film (NSF) was fabricated to extract water of crystallization from gypsum and simultaneously enable a phase transformation from gypsum to anhydrite via recrystallization. Using density functional theory ...
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The results indicate that some semi-hydrated gypsum in calcined anhydrite hydrates immediately after burning in 150°C, and the product dihydrate gypsum has seed crystal induction effect to ...
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et al.12 investigated the dehydration process of gypsum using a combination of controlled transformation rate thermal analysis and Laue diffraction, concluding that there is only one dehydration step from gypsum to γ-CaSO 4 at 500 Pa or below; whereas β-CaSO 4·0.5H 2 O is an intermediate product ...
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The influence of gypsum is mainly reflected in the last two stages, which are the change in the formation rate of hydration products and the change in morphology. Anhydrite can maintain the hydration acceleration period at 9–12 h, forming needle-shaped ettringite.
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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 ...
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The speed difference between conventionally ground dihydrate gypsum and a finely-ground anhydrite gypsum product can little if any difference at all. When anhydrite gypsum or dihydrate gypsum are spread in dry granular form, the different dissolving rates can actually be an advantage, if they are used intelligently.
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The effects of a 0, 0.2 wt%, 0.6 wt%, 1.0 wt%, 1.4 wt% and 1.8 wt% calcium hydroxide content on the microstructure and performance of super sulfated cement (SSC) were investigated.
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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 …
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1. Introduction. In the process of cement production a certain amount of gypsum is added in order to adjust setting time of cement, contribute for strength acceleration in early stage and reduce drying shrinkage of hardened cement paste [1], [2], [3].In Portland cement, usually the added gypsum is natural dihydrate gypsum, but mixed gypsum and chemical gypsum are …
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With growing demand for the development of multifunctional, high-performance, and high durable construction materials, numerous studies on calcium aluminate cement (CAC)-based cem
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In the low-temperature and high water vapor zone above curve AB in Figure Figure2 2, gypsum is thermodynamically stable; in the ABC zone, CaSO 4 ·2H 2 O will …
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The hydration properties of hemihydrate gypsum and anhydrite affect the quality of MPPG-based materials. Anhydrite has a much slower hydration rate and strength development than hemihydrate gypsum, and is commonly blended with cement, strong alkali or alkali sulfate to increase its hydration activity [15], [16], [17]. Many studies have been ...
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Natural gypsum rock (CaSO 4 ·2H 2 O) is also known as dihydrate gypsum, anhydrite, anhydrite or raw gypsum. The main components are CaO (32.6%), ... It can be seen that the expansion rate and hydration time increased linearly within 200 min, but due to the anisotropy of the sample, the increase rate of the expansion rate was different. ...
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The thermal dehydration of natural gypsum and pure calcium sulphate dihydrate (gypsum) ... (heating rate 5°C min-'), there is an increase in the hemihydrate and anhydrite content of natural and pure gypsum and possibly CaSO,.0.62 H,O could also be present. ... Calcium sulphate dihydrate electron micrographs show that the decomposition of the ...
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Therefore, the content of gypsum dihydrate was estimated to be 76.5%, based on its respective calculate percentages (96.14% and 76.50%) in CaO and SO 3. The TG-DSC curve of TG is shown in Fig. 5 (b). The weight loss in the TG curve is primarily attributed to the dehydration of gypsum (CaSO 4 ·2H 2 O) and iron hydroxide (Fe(OH) 3). The TG ...
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This subsequently raises the degree of dihydrate gypsum supersaturation. Anhydrite hydration and solution, and the spontaneous homogeneous nucleation and growth of dihydrate gypsum crystals are ...
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Setting and hardening of fresh blends of ordinary Portland cement (OPC), fired drinking water treatment sludge (DWTS) and calcined anhydrite gypsum were investigated. Sludge or Portland cement was substituted with 5 wt%, 10 wt% or 15 wt% of anhydrite gypsum. These systems lead to the preparation of supersulfated cement. These blends were shown to …
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The hydration rate of SCRM can be efficiently delayed by dihydrate gypsum, although the result is subpar. The material exhibited the lowest fluidity loss in 20 min, the setting time was extended, and the 28-day flexural and compressive strengths were raised by 26.56% and 28.08%, respectively, after adding 8 percent anhydrite.
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The enhancement in the chemically combined water with increase in the curing period may be ascribed to the increased formation of dihydrate gypsum from the anhydrite. The effect of curing period on the strength development of gypsum anhydrite-slag mixtures is shown in Fig. 1. Data show increase in the strength with the inrease in curing period.
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The temperature at which the gypsum binder (calcium sulfate hemihydrate) is industrially produced, between 80 and 180 °C, is often mentioned in the literature …
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The dehydration process of gypsum rock was studied under concentrated solar energy by using a Fresnel lens with power density of 260 Wcm 2. Temperatures higher than 700 C were attained for 1 min ...
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In view of the poor hydration activity and difficult utilization of industrial by-product fluorogypsum, the effects of potassium carbonate (K 2 CO 3) and potassium bicarbonate (KHCO 3) on the hydration mechanisms of fluorogypsum (pH-adjusted to 7.3) were investigated and compared through hydration rate, hydration heat, solubility and microscopic tests.
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In Fig. 10 g, long columnar dihydrate gypsum crystals formed in HPG280–40 % at 7 days, with some aggregations observed on the surface and vicinity of the formed dihydrate. …
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The value of n can be 0, 0.5, or 2, depending on the reaction temperature and the phosphoric acid concentration. The creation of PG solid waste has increased greatly in recent years due to the rapid development of the phosphorus chemical industry in China, the United States, Russia, Africa, and the Middle East [2, 3].PG contains impurities such as phosphorus …
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In the high-temperature and low water vapor pressure region, gypsum dehydrates to form γ-CaSO4 in a single-step process (CaSO4·2H2O γ -CaSO4); with increasing water vapor …
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