· and water vapor pressure. In the high-temperature and low water vapor. pressure region, gypsum dehydrates to form γ-CaSO4in a single-step. process (CaSO ·2HO→γ-CaSO); with increasing water
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· The gypsum-hemihydrate transformation has been long studied as a laboratory analogue for seismogenic dehydration reactions during subduction 8,9 and as a model of metamorphic dehydration reactions
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Hemihydrate occurs in two formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α
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· During the hydration process, SO 4 2− can be replaced by HPO 4 2− into gypsum crystals to form a solid solution, which further affects the gypsum performance []. In addition, the crystal morphology of CaSO 4 ·2H 2 O is modified by the impurities in phospho-gypsum, and needle-like gypsum crystals have a higher compressive strength
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· The application of α-hemihydrate gypsum (α-HH) is limited by several factors, such as a rapid hydration rate, short setting time, poor water resistance, and high cost. Especially because of the high production cost, although α-HH has excellent mechanical strength, it is rarely used in the field of building materials. In this study, based
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· The detailed dissolution process of hemihydrates were revealed: surface dissolution and particle fragmentation. Gypsum precipitates at the beginning, crystallizes rapidly after 20 min hydration and tends to be stable after 2 h hydration. The hydration reaction of hemihydrate is a process of particle size reduction.
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· The formation of beta hemihydrate is linked to the hydration process of gypsum. When gypsum (CaSO4·2H2O) is exposed to water, it undergoes partial dehydration, leading to the formation of beta hemihydrate as an intermediate product.
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· Median hemidihydrate process requirements are given in Table 2. Dihydrate-Hemihydrate Process (DHH) Although the attack and digestion sections are run under dihydrate conditions, it is not desirable to effect a very high degree of P 2 O 5 recovery during the separation of the acid from the dihydrate because the succeeding
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:Hemihydrate GypsumGypsum Hydration · Preparation of α-hemihydrate gypsum crystal is an approach for utilization of phosphogypsum (PG), but the soluble phosphorus impurities in PG have a
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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 two formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α-hemihydrate is too
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DOI: 10.1016/j.jcrysgro.2021.126360 Corpus ID: 241731164 Preparation of hemihydrate gypsum with controllable morphology in Glycerol-NaCl-Water solutions with maleic acid In this study, a simple and efficient strategy is developed to synthesize rod-shaped α
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· Titanium gypsum (TG) is rarely used to produce α-hemihydrate gypsum (α-HH) because of its poor crystallinity and high impurity and moisture contents. Here, a method is proposed to prepare α-HH by adjusting the reaction temperature, CaCl 2 solution concentration and maleic acid dosage based on acid leaching and heat-treated TG as
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When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate (bassanite, often simply called "plaster") and, if heated further, to anhydrous calcium sulfate (). As with anhydrite , the solubility of gypsum in saline solutions and in brines is also strongly dependent on NaCl (common table salt) concentration.
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· Calcium sulfate dihydrate (gypsum) is a commonly found mineral in the nature, and it is an important building material in the production of ‘Plaster of Paris’, gypsum wallboard, and Portland cement [1, 2].The CaSO 4 –H 2 O system is characterized at least five crystalline phases, which are gypsum (CaSO 4 ·2H 2 O), hemihydrates (α- and β
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· The preparation process of α-hemihydrate gypsum (α-HH) using flue gas desulphurization (FGD) gypsum and concentrated brine is illustrated in Fig. 2. This study aims to validate the feasibility of this approach and understand the influence of various brine components on the overall process [18].
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The soluble phosphorus has a negative effect on the mechanical strength of a-hemihydrate gypsum; especially when the content of soluble phosphorus exceeded 0.1%, the bending strength and compressive strength decreased obviously. The effect of different soluble phosphorus on the mechanical. 2 strength was H3PO4 > H2PO4 > HPO4 .
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:Gypsum Dehydration ProcessGypsum To Anhydrite TransformationIn this article, different forms of soluble phosphorus (H3PO4, H2PO4 and HPO4 2 ) on the setting time and mechanical properties of a-hemihydrate gypsum were stud-ied, and
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· Salt gypsum was first placed in an oven at 40 C to dry it to a constant weight. Then, it was ground using a mortar and pestle such that the particles could pass through a 200-mesh (75 μm) standard sieve. Referring to the literatures [[30], [31], [32]], the mass ratio of salt gypsum to deionized water was fixed at 0.05, the glycerol/water ratio
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· In this article, tricalcium aluminate (C 3A) was utilized as addition agent for hemihydrate gypsum (HHG) to improve the performance of gypsum pastes, and on that basis, the optimal dosage group of C3 A was selected for further study on the composite effect with nano-silica (NS). HHG plasters with 0–5% content of C 3 A and besides
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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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· It is known that the hydration of bassanite to gypsum involves a dissolution-reprecipitation process in contrast to solid-state diffusion 49, which is seemingly also the case for our gypsum
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· PG can be calcined to form the hemihydrate gypsum (β-CaSO 4 •0.5H 2 O, HPG), making it a potential substitute to natural gypsum. However, PG contains large amounts of soluble phosphorus(P) impurities, which pose a serious risk on the soil and groundwater, especially when they are abundantly accumulated and leached.
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· Phosphogypsum can be used to prepare β-hemihydrate gypsum (β-CaSO 4 ·1/2H 2 O) plaster. A prerequisite for any effective reuse of phosphogypsum is to understanded the act by which impurities in phosphogypsum influence the performance of β-CaSO 4 ·1/2H 2 O plaster, and the role NaF was explored in this study.
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· A pilot scale preparation of α-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum was conducted for the first time in mixed salt solutions under atmospheric pressure. Highlights Pilot-scale preparation of α-CaSO 4 hemihydrate from FGD gypsum in salts solution. Feasibility of salt solution recycling in
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· This work firstly shows that the observed crystallization inside of gypsum during dehydration is the formation of alpha-hemihydrate. Gypsum crystal at (a) 135 • C, and (b) 142 • C. Crystals
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· In this work, PASP with different molecular weights (2000, 4000–5000 and 6000–8000) was utilized as the retarder for α-hemihydrate gypsum (α-HH), and the effect of PASP on the coagulation, hydration and crystallization process
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· During hemihydrate gypsum hydration, the proportion of free P was higher, which mainly existed as H3PO4 and H2PO4⁻, but P species on dihydrate gypsum surface contained a higher HPO4²
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Phospho-gypsum is a by -product of phosphoric acid production. Approximately 3 ~5 tons of phosphor -gypsum are produced during the production of 1 ton of phosphoric acid [1]. The global cumulative emissions of phosphor- gypsum is approximately 6 billion tons with an increasing rate of 150 million tons/year.
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· This study aims to reveal the influence of fluoride ion (F −) on the performance of polycarboxylate superplasticizer (PCE) in hemihydrate gypsum pastes. By introducing F − into the natural hemihydrate gypsum-PCE system, workability, mechanical properties, and hydration process were systematically studied.
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· 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
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