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US20090208392A1

A process for producing alpha-hemihydrate gypsum from dihydrate gypsum includes feeding a slurry comprising the dihydrate gypsum and water into a heating tube, heating the heating tube at a temperature effective to generate steam and pressure from the water, wherein the steam and pressure are effective to convert the dihydrate gypsum to the alpha-hemihydrate gypsum, and withdrawing …

US10745278B2

Provided is a method for producing phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum including: adding a phosphate rock powder and a part of dilute sulfuric acid into an extraction tank, carrying out an extraction reaction on same, separating a clear liquid from the obtained mixed slurry, sending the clear liquid, as a finished product phosphoric acid, into an acid ...

Method for producing wet-process phosphoric acid and ...

 · The method not only reduces the content of phosphorus in the by-product alpha-hemihydrate gypsum, but also realizes the industrial production of phosphoric acid and by-products ordinary alphahemihydrate gypsum and high-purity and high-whiteness alpha-hemihydrate gypsum by a wet-process. (71) Kingenta Norsterra Chemical Co., Ltd (CN)

CDC

Calcium sulfate hemihydrate, Dried calcium sulfate, Gypsum hemihydrate, Hemihydrate gypsum [Note: Plaster of Paris is the hemihydrate form of Calcium Sulfate & Gypsum is the dihydrate form.] White or yellowish, finely divided, odorless powder.

Innovative gypsum processing at GIPS AD – samimgypsum ...

Calcined gypsum from a technical process is not a pure gypsum hemihydrate, but also consists of water-free gypsum, mostly in the form of AIII (soluble anhydrite), as well as un-calcined remains in the form of gypsum dihydrate (DH). The presence of moisture allows the reconversion of AIII into HH and, given sufficient moisture level and contact ...

CA1258961A

TITLE OF THE INVENTION: PROCESS FOR PRODUCING .alpha.-FORM GYPSUM HEMIHYDRATE ABSTRACT OF THE DISCLOSURE: Disclosed herein is a method for producing .alpha.-form gypsum hemihydrate, comprising heating an aqueous slurry containing gypsum dihydrate and a salt of sulfosuccinic acid as the catalyst for crystallization, thereby converting gypsum dihydrate into .alpha.-form gypsum hemihydrate.

ALPHA PLASTER PRODUCED BY PRESSURELESS METHOD …

The process of gradual transformation of gypsum through hemihydrate to gorgeyite is clearly apparent on radiograms and images from scanning electron microscopy, see Figures 6a and 6b. Proportionally to the decrease of NaCl proportion, the speed of said transformation is higher than in the preceding case.

The Effect of Process Conditions on the Preparation of α ...

The Effect of Process Conditions on the Preparation of α-Calcium Sulfate Hemihydrate from FGD Gypsum Using the Hydrothermal Method under Atmospheric Pressure May …

Hemihydrate

Depending on the process and type of gypsum, making of 1 kg of β-hemihydrate typically produces 0.097 kg equivalent of CO 2 and generates a primary energy demand of ∼1.49 MJ. 203 As a consequence, gypsum could gain even more importance in the future as an environmentally friendly mineral binder system for dry mortars.

The path to gypsum is four steps long

 · The group reported that gypsum actually forms in a three-step process: precipitation of nanocrystals of bassanite — or calcium sulfate hemihydrate, with one water molecule for every two calcium sulfate units — followed by the assembly of those crystals into larger aggregates, and finally transformation of the aggregates into gypsum.

PROCESS FOR CONTINUOUS MODIFICATION OF DIHYDRATE GYPSUM …

1. 1.-17. (canceled) 18. A process for modifying dihydrate gypsum, comprising: a calcination step of subjecting the dihydrate gypsum as a starting raw material to calcination to convert the dihydrate gypsum into hemihydrate gypsum, a recrystallization step of using a slurry with the hemihydrate gypsum, which has been obtained in the calcination step, contained as solid matter therein, and ...

11.16 Gypsum Manufacturing

wallboard, gypsum must be partially dehydrated or calcined to produce calcium sulfate hemihydrate (CaSO4 ½H 2O), commonly called stucco. A flow diagram for a typical gypsum process producing both crude and finished gypsum products is shown in Figure 11.16-1. In this process gypsum is crushed, dried, ground, and calcined.

Alpha Hemihydrate Gypsum Preparationed by Atmospheric ...

Alpha Hemihydrate gypsum was prepared through atmospheric pressure salt solution method based on orthogonal experiments. The morphology and phase composition of the samples were observed and analyzed by microscope and X-ray diffractmeter. The major experimental parameters of atmospheric salt solution that prepared alpha half water gypsum were determined.

The α

Kelley, Southard and Anderson1 have shown that the thermodynamic properties of calcium sulphate hemihydrate depend on whether the hemihydrate is produced from gypsum calcined in …

Hydration characteristics and mechanism analysis of β ...

 · 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 …

New Development in Dihydrate -Hemihydrate processes: …

New Development in Dihydrate -Hemihydrate processes: The new Prayon DA-HF process Tibaut Theys Prayon ... • Double crystal process • Gypsum seallable • Stacking issue solved • 90% of gypsum sold . Dihydrate Process H 2 SO 4 98% Phosphate Recycled acid Water Dihydrate Typical P 2 O 5

Crystallization Kinetics of α-Hemihydrate Gypsum Prepared ...

According to the difference in hydration, calcium sulfate can be divided into dihydrate gypsum (CaSO 4 ·2H 2 O), hemihydrate gypsum (CaSO 4 ·0.5H 2 O), and anhydrite (CaSO 4) [1,2,3].Phosphogypsum (PG) is mainly composed of calcium sulfate dihydrate (DH), which is a byproduct from the wet process of phosphoric acid production.

Calcium sulfate hemihydrate treatment process

 · The new treatment process works well with synthetic gypsum by reducing the water demand with increasing treatment time. Note that once again the process resulted in a reduction in both the soluble anhydrite content and the residual gypsum content, turning both into hemihydrate.

Microstructure and mechanical properties of β-hemihydrate ...

 · Therefore topics such as the hydration induced properties, and especially the behavior of the β-hemihydrate upon hydration to produce gypsum (plasterboard) is still poorly understood. This article addresses the properties of gypsum (plasterboard) produced from a β-hemihydrate from its hydration process.

Gypsum

Gypsum is moderately water-soluble (~2.0–2.5 g/l at 25 °C) and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures. 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 ().

Crystallization Kinetics of -Hemihydrate Gypsum Prepared ...

 · gypsum (CaSO4 2H2O), hemihydrate gypsum (CaSO4 0.5H2O), and anhydrite (CaSO4) [1–3]. Phosphogypsum (PG) is mainly composed of calcium sulfate dihydrate (DH), which is a byproduct from the wet process of phosphoric acid production. It is estimated that every ton of phosphoric acid produces about 4.5 to 5.5 tons of PG [4,5] in the world. A large

Determination of Calcium Sulfate Dihydrate and Hemihydrate ...

Without gypsum, hydrated calcium aluminate crystallizes within about 10 min; gypsum retards this process by several hours or even days depending on the gypsum content. In the quality control of cement, it is therefore important to know the exact content of the CaSO4 dihydrate or hemihydrate.

Study of Fresh and Hardening Process Properties of Gypsum ...

 · Hemihydrate gypsum with high purity and minimum flexural resistance of 3.5 N/mm2 (according to UNE-EN 13279:2006 [14]), codified as E-35 and classified as Euroclass A1 (without fire contribution) according to 89/106/CEE Directive, is used in this experimentation as the matrix of all materials formulated.

The Effect of Process Conditions on the Preparation of α ...

This paper studies the laws of crystal growth, percent conversion and the rate of reaction of α-calcium sulfate hemihydrate from FGD gypsum under different conditions using the hydrothermal method under atmospheric pressure. The crystal morphology was observed by using SEM, polarizing microscope profile, and percent conversion and the rate of reaction were obtained by assaying crystal water ...

Process for producing α-form gypsum hemihydrate

Neverthless, when a process for producing α-gypsum is combined directly with a desulfurization process of exhaust gases, the medium for producing gypsum hemihydrate is fundamentally the same as the absorbent liquid in the desulfurization process of exhaust gases, and the adjustments of pH, concentration and dilution of the liquid only can be done.

Effect of Aluminum Sulfate and Succinic Acid on the Growth ...

 · The existing α -hemihydrate gypsum preparation process has low production efficiency and high energy consumption. In this paper, α -type hemihydrate gypsum was prepared by microwave irradiation using phosphogypsum as the raw material, calcium chloride solution as the reaction medium, and succinic acid and aluminum sulfate as crystal-transforming agents.

PROCESS FOR PREPARING GYPSUM HEMIHYDRATE

PROCESS FOR PREPARING GYPSUM HEMIHYDRATE . United States Patent 3615189 . Abstract: Stable calcium sulfate hemihydrate is produced by suspending particulate gypsum in a reaction mixture comprising a water solution of a water-soluble inorganic salt such as a salt of an alkali metal, an alkaline earth metal or ammonium, and at least one of the ...

Preparation of Whitening Dihydrate Gypsum and Short ...

 · Using FGD gypsum as the raw material, whitening and large prismatic dihydrate gypsum can be obtained by dissolution‐crystallization and decoloring process with α‐hemihydrate gypsum whiskers prepared in MgSO 4 ‐CaCl 2 ‐H 2 O solution, which can transform into whitening short columnar α‐hemihydrate gypsum. The effects of aging temperature, pH, dosage of sodium dodecyl sulfonate …

What Is Gypsum | What Is Gypsum Plaster | Gypsum ...

 · First, the gypsum rock is ground and crushed in the mill to start the process. After that gypsum is heated up on a flat metal plate above a kiln. Heating the gypsum at 120°C for one-hour results in a hemihydrate (CaSO4.1⁄2H2O) – with three-quarters of the water removed. This Gypsum hemihydrate is known as Plaster of Paris.

Gypsum Calcination

Gypsum Calcination. Calcination is the practice of dehydrating gypsum into plaster or stucco through a batch or continuous process which includes heating the gypsum to evaporate the crystalline water. Typically, free water is removed in an initial process at approximately 45℃ and crystalline bound water is removed in a second process at 120 ...

Global Gypsum Knowledge Base, news, plants & more on the ...

Paper 14 Gypsum-based construction materials – How to protect against microbes: Dr. Wolfgang Lindner, Technical Director for Asia: Troy Corporation. Paper 15 Investigation of the hydration process of calcium sulphate hemihydrate by ESEM and other methods: Christian Pritzel: University of Siegen

Gypsum Crystallization during Phosphoric Acid Production ...

 · process (x = 2, gypsum as the final crystal form) and the nondihydrate process (also known as the hemihydrate process because hemihydrate is involved, although it is not necessarily the final crystal form). The dihydrate process is the earliest developed industrial phosphoric acid …

US20090208392A1

Calcium sulphate hemihydrate hydration leading to gypsum ...

Microstructure and mechanical properties of β-hemihydrate ...

the b-hemihydrate upon hydration to produce gypsum (plaster-board) is still poorly understood. This article addresses the proper-ties of gypsum (plasterboard) produced from a b-hemihydrate from its hydration process. The water demand of b-hemihydrate, as well as the flowability of the hydrating system was investigated by the common spread ...

US4842842A

Disclosed herein is a method for producing α-form gypsum hemihydrate, comprising heating an aqueous slurry containing gypsum dihydrate and a salt of sulfosuccinic acid as the catalyst for crystallization, thereby converting gypsum dihydrate into α-form gypsum hemihydrate.

PRAYON PROCESS fOR PhOSPhORiC ACid

purity and quality of the gypsum must be very high. To fulfil these requirements, the process used at our unit is the two-stage ... stage leads to a single-stage hemihydrate process known as Ph1. this can yield acid 39-45% P 2 o 5, with a process efficiency of up to 95%. if lower strengths are accept -

Thermal analysis of calcium sulfate dihydrate sources used ...

 · The core composition of gypsum wallboard is calcium sulfate dihydrate (CaSO 4 ·2H 2 O) with varying impurities, additives, or both. This study compares here two commercially calcined sources of hemihydrate (CaSO 4 ·½H 2 O) from a natural source and a synthetic by-product of flue gas desulfurization and neutralization to reagent grade hemihydrate. Two common ingredients, borax and …

USG Gypsum Misconceptions White Paper (English)

The process of cooking gypsum is called "calcination." As previously mentioned, two molecules of water are part of the gypsum (dihydrate) crystal. The calcination process removes 75% of the water, yielding a crystal composition known as calcium sulfate hemihydrate. Adding water to hemihydrate converts it back to the original form,

AP-42, CH 8.9: Phosphoric Acid

U. S. generally use a dihydrate process that produces gypsum in the form of calcium sulfate with ... Japanese facilities use a hemihydrate process that produces calcium sulfate with a half molecule of water (CaSO4 ½H2O). This one-step hemihydrate process has the advantage of producing wet process phosphoric acid with a