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Facile preparation of α-calcium sulfate hemihydrate whisker …

Lactic acid gypsum (LAG), the by-product from lactic acid preparation, has caused land occupation and environmental pollution. Herein, hemihydrate gypsum (HHG) whisker, an inorganic material with excellent performance, prepared using LAG as the raw material via atmospheric pressure salt solution method was investigated. Nitrate …

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Eco-friendly, high-toughness gypsum prepared using hemihydrate

Phosphogypsum (PG), an industrial byproduct of wet-process phosphoric acid production, is mainly composed of calcium sulfate dihydrate (CaSO 4 · 2H 2 O). According to statistics, each ton of phosphate fertilizer will yield approximately five tons of PG [1].China is among the largest PG producers worldwide, with a cumulative stockpile of …

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Gypsum products | PPT

13. SETTING REACTIONS There are three theories of gypsum setting. The colloidal theory proposes that, when mixed with water, hemihydrate enters into the colloidal state through a sol-gel mechanism. In the sol state, hemihydrate particles are hydrated to form dihydrate, thereby entering into an active state. As the measured amount of water …

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Preparation of alpha-calcium sulfate hemihydrate from FGD gypsum …

This work develops a new class of salt solution method to prepare alpha-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum in trace K 2 SO 4-contained 4.0 M Ca(NO 3) 2 aqueous solution at 95 °C under atmospheric pressure. The driving force for the phase transition is provided by the concentrated Ca(NO 3) 2 …

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Autoclave‐Free Formation of α‐Hemihydrate Gypsum

Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the …

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Synthesis of α-hemihydrate gypsum from cleaner phosphogypsum

α-hemihydrate gypsum is synthesised by mild method from cleaner phosphogypsum. ... "Wet method" is an economic process of preparing phosphoric acid and is widely applied in phosphate fertiliser industry. ... (which is widely used in industrial production) for ease of utilisation. In the water-washing pre-treatment, the traditional …

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Frontiers | Impact of carboxylic acid structure on α-hemihydrate gypsum …

1 Introduction. Phosphogypsum (PG), a major by-product of wet-process phosphoric acid production, poses a significant environmental challenge. Global PG production is estimated at approximately 5 tons per ton of phosphoric acid [], resulting in massive accumulations, particularly in China, where over 830 million tons are stockpiled, …

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Hemihydrate

Gypsum and anhydrite are naturally occurring minerals, however the hemihydrate and anhydrite can be obtained by calcination which is a process of chemical alteration by heating the dihydrated gypsum at temperatures of 125 °C-180° C and higher than 300 °C, respectively, as shown in Fig. 11 [30,31,20,32].

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Microstructure and mechanical properties of β-hemihydrate …

The hydration process of the β-hemihydrate was investigated applying an ultrasonic wave method and the influence of the water content on hydration was …

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Understanding gypsum in 3 diagrams

According to Lavoisier and Le Chatelier, 9 the reaction is a process of dissolving hemihydrate to create a super saturated solution of gypsum, from which …

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CN102659331A

The invention discloses a steam pressing production process for alpha-hemihydrate gypsum, which relates to a gypsum processing technology, and is used for solving the problems of long normal pressure drying time and low thermal efficiency existing in the conventional process. The process comprises the following steps of: (1) putting …

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Preparation of α-calcium sulfate hemihydrate from …

Using solar energy to dehydrate gypsum to produce β-hemihydrate is one way to improve the carbon footprint 13,14 . Alternatively, α-hemihydrate is produced from gypsum using an autoclave process ...

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Gypsum hydration: a theoretical and experimental study

dissolution of hemihydrate in the first stage and the nucleation and precipitation of dihydrate in the second stage. 2. Gypsum hydration is strongly influenced by water amount. Spread flow test is suitable to determine the water demand for gypsum hydration. An excess of water is needed for good workability for the gypsum plasterboard production …

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Hemihydrate

Gypsum and anhydrite are naturally occurring minerals, however the hemihydrate and anhydrite can be obtained by calcination which is a process of chemical alteration by …

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Effect of Phosphoric Acid on the Preparation of α …

1. Introduction. Phosphogypsum is a by-product of the wet process phosphoric acid industry [1,2,3].Approximately 5 tons of phosphogypsum are generated …

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Calcium sulphate hemihydrate hydration leading to gypsum

Depending on the process of industrial production, hemihydrate occurs in two different forms (α- and β-forms); α-form is prepared by wet method (e.g., autoclaving) and β-form is prepared by dry methods (e.g., calcining) from calcium sulphate dihydrate [16], [17], [18], [19].In the laboratory [19] β-hemihydrate is prepared from the dihydrate …

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Calcium sulfate whisker prepared by flue gas desulfurization gypsum…

1. Introduction. Desulfurization gypsum is an industrial by-product formed by desulfurization of flue gas generated by power plants, petrochemical plants, steel plants and other industries [1].China is the world's largest coal producer and consumer [2].The large consumption of coal leads to huge stockpiles of desulfurization gypsum [3].The toxic …

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Preparation of α-High-Strength Hemihydrate from …

An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl3 solution was used to promote the …

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Mechanism and kinetics of gypsum–anhydrite

Contrary to the gypsum behavior at 90 °C, in the experiments performed at elevated temperatures inside the autoclave, the transformation process proceeded faster, and a different transformation mechanism was observed.In the experiments performed at 150 °C, more than 90% of gypsum transformed to hemihydrate after 2 h retention time, …

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Calcium sulphate hemihydrate hydration leading to gypsum

The mechanism of gypsum crystal growth during hemihydrate hydration in the absence and presence of chemical additives is discussed in this article. Section snippets Hemihydrates. Depending on the process of industrial production, hemihydrate occurs in two different forms (α- and β-forms); α-form is prepared by wet method (e.g., …

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ALPHA GYPSUM POWDER VS BETA GYPSUM POWDER

1.Hemihydrate gypsum has two forms: α and β, both of which are rhombic crystals, but their physical properties are different. α-type hemihydrate gypsum has good crystallinity and firmness. β-type hemihydrate gypsum is a flaky and cracked crystal with excellent crystals. ... DIFFERENT PRODUCTION PROCESS. Typically, α-type hemihydrate …

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Transformation of Flue-Gas-Desulfurization Gypsum to (α …

It has been estimated that annual production of FGD gypsum in China will reach 90 million tons by 2020 [1] and its disposal is a major problem for power plants. ... 123 130 (1997). 15 Gioia, F., Mura, G., Viola, A., “Analysis, simulation, and optimisa- tion of the hemihydrate process for the production of phosphoric acid from calcareous ...

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Salt Refining Technology at Zhongjingba Site in Nineteenth …

The byproduct of salt gypsum generated in the process of salt production is generally composed of anhydrous gypsum (CaSO 4), hemihydrate gypsum (CaSO 4 ·(1/2)H 2 O) and dihydrate gypsum (CaSO 4 ·2H 2 O) (Klepetsanis et al. 1999; Tang et al. 2011:27–30). Theoretically, the higher the heating temperature during salt making, the …

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Preparation of α-hemihydrate gypsum whiskers from …

A substantial stockpile of phosphogypsum (PG) not just consumes land resources, but also poses environmental contamination risks. Herein, the conversion of PG into high-value α-hemihydrate gypsum (α-HH) whisker by the atmospheric pressure salt solution method with simple process, high efficiency and low energy consumption was …

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Effect of modifiers on crystalizing habit and mechanical …

α-Hemihydrate gypsum (α-HH) is known as high strength gypsum, the strength of α-HHs is three times larger than that of building gypsum, ... However, most studies prepared the HH crystals by salt solution method, which had more complex process and lower production efficiency by comparation with the autoclaving method.

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Recycling, reusing and environmental safety of industrial by …

Industrial by-product gypsum is a solid waste produced in industrial production process. With the acceleration of the industrialization process, the productivity of various industrial by-products gypsum has increased year by year. ... SG was a composite of anhydrous gypsum, hemihydrate gypsum and dihydrate gypsum. Table …

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New insights into the growth characteristics and crystal …

The stockpiling of phosphogypsum (PG) poses a substantial risk of environmental pollution.To reduce the stockpile of PG and enhance its value, this research utilized phosphogypsum to produce α-hemihydrate gypsum (a-HH).The study elucidates the crystallization process of α-HH, which involves Ca 2+ helical growth and …

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Experimental Study and Mechanism Analysis of …

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. …