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In this paper, the dihydrate–hemihydrate recrystallization method was employed to produce β-hemihydrate gypsum. The effects of thermodynamic conditions such as temperature, sulfuric acid concentration, and phosphoric acid concentration on the removal of F and P impurities were investigated. Kinetic studies revealed that the …
In this article, tricalcium aluminate (C 3 A) 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 C 3 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 …
1. Introduction. Phosphogypsum is a by-product of the wet process phosphoric acid industry [1,2,3].Approximately 5 tons of phosphogypsum are generated per ton of phosphoric acid production [].At present, the annual emission of phosphogypsum in the world has exceeded 280 million tons, but the comprehensive utilization rate is only …
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].
Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. This dehydration process is technically performed in three different ways.
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 production technology.
Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water …
This is a two-stage process with calcium sulphate hemihydrate formed in the first stage being transformed to dihydrate gypsum in the second stage prior to discharge as a by-product. The filter acid may be further concentrated by evaporation, if required, for downstream uses. 2. Basics of Hemihydrate (HH) Process 2.1.
Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the …
Phospho-gypsum is an industrial solid waste discharged from the phosphate production process. The waste includes complex impurities such as phosphoric acid and its salts, fluoride, and organics. ... (Peak II). It is evident that hemihydrate gypsum containing Na 2 HPO 4 had a longer peak II than S4 (0.06 wt.% retarder), because the …
A microscopic mechanism of efflorescence on hemihydrate gypsum: insight into the formation and diffusion of sodium impurities in hemihydrate gypsum crystals. Colloids Surf. A Physicochem. Eng. ... a physical–chemical coupling production process. Chin. J. Chem. Eng., 28 (8) (2020), pp. 2221-2226, 10.1016/j.cjche.2020.05.021.
The gypsum-hemihydrate transformation has been long studied as a laboratory analogue for seismogenic dehydration reactions during subduction 8,9 and as …
1. Introduction. Gypsum, an important mineral resource, is widely used in the chemical industry [1], agriculture [2], medical treatment [3], building materials [4], food [5], and other fields, which mainly come from natural and industrial by-products.In the field of chemical industry, gypsum is commonly used as a raw material for the production of …
1. Introduction. Phosphogypsum (PG) is the main solid waste in the phosphorus chemical industry. In the wet process production of phosphoric acid, which is a mainstream process of the phosphorus chemical industry, 4.5–5.5 tons of PG is emitted for each ton of P 2 O 5 production [1], [2], [3].The PG is mainly composed of dihydrate …
In recent years, the massive accumulation of industrial by-product gypsum, especially flue gas desulfurization (FGD) gypsum and phosphogypsum (PG), not only encroaches on lands but also causes serious environmental pollution. The preparation of α-calcium sulfate hemihydrate (α-HH) from industrial by-product gypsum is an important …
Phospho-gypsum is an industrial solid waste discharged from the phosphate production process. The waste includes complex impurities such as phosphoric acid and its salts, fluoride, and organics.
WEBprocess (x = 2, gypsum as the final crystal form) and the nondihydrate process (also known as the hemihydrate process because hemihydrate is involved, …
The calcium sulphate dihydrate gypsum (CaSO 4 ·2H 2 O) is the most common sulphate evaporite mineral on our planet 1.Sulphate evaporites play an important role in Earth's sulphur cycle and are ...
The hydration process of the β-hemihydrate was investigated applying an ultrasonic wave method and the influence of the water content on hydration was analyzed. ... there are 160 quarries for gypsum production and the number of employees is over 85,000 [2]. The CaSO 4 ·H 2 O system is composed of five solid phases: dihydrate, ...
Hemihydrate gypsum (CaSO 4 ·0.5H 2 O, HH) is a kind of air-hardening cementitious material, which is widely applied in building and decoration materials, ... Kudo Y. Process for Production α-Form Gypsum Hemihydrate. 4842842. U.S. Patent. 1989 June 15; 13. Duan Z., Qin H., Li G., Tang X., Wen Z. Research on crystal form modifying …
The hydration of calcium sulphate hemihydrate (CaSO 4 ·0.5H 2 O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO 4 ·2H 2 O) has been the subject of several investigations over a long period and a vast amount of data is widely distributed throughout in the literature. In this review article an overall picture of the …
DOI: 10.1021/acs.iecr.0c03305 Corpus ID: 224895914; Unraveling a Sustainable Process for the Production of High-Strength α-Gypsum Using Soda Residues and H2SO4 @article{Wang2020UnravelingAS, title={Unraveling a Sustainable Process for the Production of High-Strength $alpha$-Gypsum Using Soda Residues and H2SO4}, …
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., …
The effects of phosphoric acid (H3PO4) in pressurized aqueous solution on the dehydration of CaSO4·2H2O to form α-hemihydrate gypsum (α-HH) phase and the regulation of crystal shape were studied in this paper in order to provide guidance for the low-cost and high-value utilization of phosphogypsum. The results showed that H3PO4 …
In this paper, the solid waste desulfurization gypsum produced by coal-fired power plants was used as a raw material to prepare calcium sulfate whiskers with high application prospects. Calcium sulfate whiskers with uniform morphology and high aspect ratio can be prepared by hydrothermal method in sulfuric acid solution. A new process …
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 …
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 …
Phosphogypsum (PG), a waste product of the phosphate fertilizer industry, is a source of environmental pollution.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 …
Semantic Scholar extracted view of "Utilization of phosphogypsum to synthesize α-hemihydrate gypsum in H3PO4–H2O solution" by Long Chen et al. Skip to search form Skip to main ... ion concentration are important for improving the conversion rate of α-HH–DH and the purity of DH products in the production of wet process …
To achieve more profitable products, much attention has been paid to the development of FGD gypsum markets in the production of α-calcium sulfate hemihydrate ... D.W. Kirk, S. Tong, Process for the production of α-hemihydrate calcium sulfate from flue gas desulfurization materials, CA Patent 1996 CA2167978. Google Scholar
Calcium Sulfate Hemihydrate, also known as plaster of Paris, is a material made from gypsum that has been used for centuries in construction and various medical applications, including bone repair and growth factor release. ... In contrast, if water is supplied during the setting process, the gypsum crystals can grow further. For absorption ...
One process of forming alpha-hemihydrate gypsum involves placing calcium sulfate dihydrate in an autoclave in the presence of saturated steam at elevated pressure over an extended period of time. This method can be used for autoclaving of lump or ground gypsum. ... As described herein, reference has been made to the production of alpha ...
Flue gas desulfurization (fgd) is a waste incineration process that employs limestone slurry (CaCO 3) as a scrubber to remove SO 2 from exhaust gases, thereby reducing pollutant emissions. CaCO 3 reacted with SO 2 to form calcium sulphite (CaSO 3), which was then oxidized to form anhydrite (CaSO 4) and gypsum (CaSO 4 ⋅2H 2 O), …
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.
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 …
Direct production of high-strength α-calcium sulfate hemihydrate (α-HH) with no additives was accomplished by the reaction of aluminum sulfate and waste CaCl 2 discarded from Solvay soda plant. For scaling-up this new process, the crystallization kinetics of α-HH was experimentally investigated under varying conditions including …
The morphology of hemihydrate phosphogypsum crystals is of vital importance in the hemihydrate–dihydrate (HH–DH) wet-process phosphoric acid production for high filtration strength.