Utilization of phosphogypsum to synthesize α-hemihydrate gypsum …

Phosphogypsum (PG) is a kind of industrial solid waste with high impurity content and low utilization rate. 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 …

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Utilization of low-quality desulfurized ash from semi-dry flue gas

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 ...

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Understanding gypsum in 3 diagrams

Beta hemihydrate is formed when gypsum is heated up to around 100°C in a normal open kettle or rotary kiln. Alpha hemihydrate is formed in an autoclave above 100°C in a water (suspension autoclave) or in a steam autoclave. 5 - 7 This is possible as, above 100°C, hemihydrate becomes less soluble than dihydrate. The solubility of dihydrate ...

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Preparation of Medium–Low Strength Hemihydrate Gypsum from …

This study explored the production of a medium–low strength α-hemihydrate gypsum (α-HH) from phosphogypsum using an autoclaved method. The influence of slurry concentration, spreading thickness, crystallizing agents, slurry pH, autoclaving temperature, and autoclaving time on the properties of α-HH was investigated. The energy consumption of …

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Preparation of α High-Strength Gypsum from FGD Gypsum by …

This paper introduced the characteristics of α high-strength gypsum preparation from FGD gypsum by autoclaved semi-dry process. The compositions of the product in different stages of the reaction and the effects of crystal modifiers on the morphology of the α-HH crystals were examined and compared. The properties of α-HH and the feature of hydration products of α …

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Structural evolution during the dehydration of gypsum materials

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 has been determined …

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KGS--Gypsum in Kansas--Geology

The development of a multimillion-dollar gypsum industry was made possible by the following factors: (1) Gypsum is an abundant, naturally pure raw material. (2) It can be dehydrated to the hemihydrate at relatively low …

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The influence of calcium formate on the hydration of calcium …

The gypsum powder was stored for 24 h in a 100 °C oven, where mainly it dehydrated into hemihydrate, next to small amounts of anhydrite. ... The calculated saturation indices from porewater data of both gypsum and hemihydrate are reflecting one another in each sample and follow the sulfur concentrations (Fig. 6). The saturation of hemihydrate ...

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Gypsum hydration: a theoretical and experimental study

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 …

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Insight into the influences of β-hemihydrate and dihydrate gypsum …

Dihydrate and β-hemihydrate gypsum exhibit relatively higher solubility and dissolve more quickly than CaSO 4. However, there is little information on their incorporation in CAC. Although Zhang et al. [19] analysed the influence of the type and dosage of calcium sulphate on the properties of CAC-based materials, they did not study phase ...

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Gypsum: an investigation of microstructure and mechanical …

dehydration still needs further investigation, especially the behaviour of the β-hemihydrate and gypsum produced from it is still poorly understood. This article focuses on the role of water on the properties of gypsum produced from a β-hemihydrate due to its combined effect on both hydration and dehydration.

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Anion water in gypsum (CaSO4·2H2O) and hemihydrate …

The changes of crystal structure of gypsum on heating are evaluated by X-ray diffraction. The XRD data of gypsum, hemihydrate and anhydrite indicate that most of the peaks (2θ versus intensity) are different from each other. There are three major peaks at 11.59°, 20.72° and 29.11° 2θ in gypsum, 14.75°, 29.70° and 31.86° 2θ in hemihydrate and only 25.44° 2θ in …

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Discrimination of bassanite and anhydrite III dehydrated from …

Gypsum_120 120 h 120(±5) °C Gypsum_180 16 h 180(±5) °C Gypsum_250 16 h 250(±5) °C Gypsum_380 16 h 380(±5) °C Gypsum_550 16 h 550(±5) °C For the dehydrated gypsum samples the loss on ignition was determined. To determine the experimental loss on ignition a reference gypsum sample was dehydrated at 800 °C and weighed out.

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From atom level to macroscopic scale: Structural mechanism of …

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 …

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The hydration of calcium sulphate hemihydrate

Only gypsum dehydrated in a vacuum or in a very low water pressure is likely to rehydrate. The mechanism "Le Chatelier" would not be only one to apply during hydration with liquid water. ... The dehydration conditions of calcium sulphate dihydrate can strongly modify the rehydration mechanism of the hemihydrate. Only gypsum dehydrated in a ...

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Insights Into the Micromechanics of Dehydration‐Induced Gypsum …

Dehydrated phases (Hemihydrate and γ-Anhydrite) are formed as exfoliated pseudomorphic flakes through topotactic transformation along [010] and show two sets of oppositely dipping slip systems. During the late dehydration stage (120–140°C), plastic strain is accommodated by the sliding of these flakes along with inelastic pore compaction ...

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Quantitative determination of anhydrite III from dehydrated gypsum …

Gypsum (calcium sulfate dihydrate, Fluka, 99.9% purity) samples were dehydrated at temperatures from 85 up to 800 °C 25 g of substance was weighed in corundum crucibles of 60 ml size and dehydrated in two different furnace types to cover the complete temperature range.The furnaces were calibrated with thermo elements.

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Crystallization Kinetics of α-Hemihydrate Gypsum Prepared by

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) patterns were applied …

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Formation of α-Hemihydrate Inside of a …

This work firstly shows that the observed crystallization inside of gypsum during dehydration is the formation of alpha-hemihydrate. Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials …

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Preparation of α-hemihydrate gypsum from phosphogypsum in …

The industrial application of PG is mainly focused on building gypsum (β-CaSO 4 ·0.5H 2 O) [5], α-hemihydrate gypsum (α-CaSO 4 ·0.5H 2 O, α-HH) [6], [7], cement retarder [8], sulfuric acid co-production cement [9], soil conditioner [10] and so on. Among which, the preparation of α-HH using PG is one of the most profitable approaches because α-HH is a …

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Dehydration Pathways of Gypsum and the Rehydration …

In this work, the dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite were mainly investigated by thermodynamic modeling and MC simulations. The …

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Utilization of low-quality desulfurized ash from semi-dry flue …

Alpha-hemihydrate gypsum B a Alpha-hemihydrate gypsum a a a a a a b Dihydrate gypsum b b b c Calcium hydroxide d Calcium carbonate e Hemihydrate calcium sulfite c c c d e d d e e Fig. 1. Particle size distributions and XRD patterns of hemihydrate gypsum and desulfurized ash. H. Li, et al. Fuel 255 (2019) 115783 2

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Development of alternative for gypsum-based plaster using …

Nesquehonite (NQ) can be activated via thermal treatment under 50–175°C, after which the dehydrated nesquehonite can hydrate to form a plaster-like product, like gypsum-based plaster. Here, we developed different blends of NQ and hemihydrate (dehydrated gypsum) to produce plaster.

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From atom level to macroscopic scale: Structural mechanism of gypsum

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 to confusion between crystals …

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Innovative synthesis of high-strength α-hemihydrate gypsum: …

High-strength gypsum is the recognized designation for α-hemihydrate gypsum, often referred to as α-HH (CaSO 4 ·0.5H 2 O), which is a cementitious material with low water requirement and high strength [8].The strength of α-HH is generally between 25 and 50 N/mm 2, which is three times that of ordinary building plaster, and has superior working performance. α …

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Structural evolution during the dehydration of gypsum materials

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 materials.

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Dehydration Pathways of Gypsum and the Rehydration …

where P H 2 O(gypsum–hemihydrate) is the equilibrium water vapor pressure of the reaction for the transformation of CaSO 4 ·2H 2 O into β-CaSO 4 ·0.5H 2 O, P H 2 O(gypsum–anhydrate) represents the dissociation pressure of β-CaSO 4 ·0.5H 2 O dehydrated to form γ-CaSO 4, and P H 2 O(hemihydrate–anhydrate) naturally denotes the ...

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Soil stabilization with gypsum: A review

Factors affecting these results include the type of added gypsum (for example when hemihydrate calcium sulfate, i.e. bassanite, is used instead of gypsum, or when solid waste byproducts such as titanium gypsum, phosphorous gypsum, and desulfurization gypsum are used instead of pure gypsum), the type and percentage of fine portion of the soil ...

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Dehydration Pathways of Gypsum and the Rehydration Mechanism …

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 dehy …

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Modification on the Performance of the Hemihydrate Gypsum …

The objective of this study was to assess the feasibility of using the plant-source polymer of the matcha powder as a composite admixture for hemihydrate gypsum. Hemihydrate gypsum was mixed with different contents of matcha powder, and then the water requirement for the normal consistency, setting times, density, strength, hydration and microstructure of the …

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