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In this study, phosphogypsum (PG) is simulated by doping fluorine and phosphorus ions in an analytically pure reagent of gypsum dihydrate. The influence of fluorine and phosphorus impurity and content on the dehydration reaction process of phosphogypsum and its crystalline micromorphology is assessed during the preparation of α-type gypsum …
Alpha-calcium sulfate hemihydrate (α-HH) has been prepared from flue gas desulfurization (FGD) gypsum with salt solution method under atmospheric pressure. X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), optical micrograph, X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry …
The curve of the hemihydrate solubilities is largely based on the data of Partridge and White (), Posnjak (), D'Ans et al. and Power et al. yielding a gypsum to hemihydrate transition temperature of 99 ± 4°C, which is in reasonable agreement with the values of 97.5°C (Posnjak 1938) and 97°C (D'Ans et al. 1955).According to Fig. 2 the …
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate (CaSO4·2H2O). It is commonly found in sedimentary rock formations and is often …
The synthesis of hemihydrate gypsum (α-HH) crystals with a low aspect ratio is of great significance to practical production for the effective utilization of flue gas desulfurization (FGD) gypsum. In this work, the hexagonal prismatic α-HH crystals with controllable morphology were prepared in Glycerol-NaCl-Water solutions with maleic …
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 ...
1. Introduction. Gypsum is a material in which the amount of water of crystallization varies with its surrounding conditions, such as temperature or humidity, and can be classified into three groups, namely, calcium sulfate anhydrite (CaSO 4), calcium sulfate hemihydrate (CaSO 4 ∙1/2H 2 O), and calcium sulfate dihydrate (CaSO 4 ∙2H 2 …
hemihydrate gypsum, and the influence degree of different forms of soluble phosphorus is unclear. Therefore, the utilization of a-hemihydrate gypsum is greatly limited. In this study, the effect of soluble phosphorus on the setting time and mechanical properties of a-hemihydrate gypsum was investi-gated by adding different amounts of H 3PO 4 ...
The White Sands National Monument in New Mexico is known for its vast dune fields of pure gypsum sand. Mexico: Mexico has significant gypsum deposits, particularly in the states of Nuevo León, Chihuahua, and Coahuila. Canada: Gypsum deposits are found in provinces like Nova Scotia, Newfoundland and Labrador, and …
Depending on different preparation conditions [8,9], it can obtain two forms of hemihydrate gypsum, α- and β- hemihydrate gypsum, which are denoted as α-HH and β-HH, respectively. Many scholars believe that the cell parameters of α-HH and β-HH are identical since no obvious differences between the two forms have been concluded by …
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 …
Flue gas desulfurization (FGD) gypsum, which is mainly composed of DH, was used as raw material to obtain α-HH through dehydration in a Ca–Mg–K–Cl-solution medium at 95°C under atmospheric pressure.
and structural retarded hemihydrate (the former with added setting retarder). The hemihydrate occurs in two forms: [3 and ~. The [3 product is obtained by partial dehydration of the gypsum rock at 150-165~ This is a very low tem- perature compared with that required for lime (about
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 …
1. Introduction. Gypsum plaster, also known as plaster of Paris, is one of the earliest materials used for construction [1], [2], [3], whose use can be traced back to several thousands of years ago.Now, it is still primarily used for indoor applications owing to a whole bunch of advantageous attributes, such as easy fabrication feature, thermal …
this condition the slump is zero which indicates the minim water/hemihydrate should be 0.55 to promise a fluid gypsum plaster which is in line with the sprinkling method result. The deformation coefficient (Ep, the slope of the trend line) indicates the sensitivity of the tested materials to the water on the workability.
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 to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. This …
The apparent empirical activation energies (Ea) suggest that the transition from gypsum to hemihydrate is mainly controlled by nucleation and growth mechanism, while the transition from gypsum to γ-anhydrite is mostly followed by phase boundary mechanism. ... Impact of limestone fineness on cement hydration at early age. Cement …
An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl 3 solution was used to promote the …
The applications of gypsum in China are primarily twofold: the preparation of high-strength gypsum, construction gypsum, composite cementing materials, and others, and the preparation of gypsum building products like gypsum board and gypsum blocks. Among these, α-hemihydrate gypsum (α-HH) is a high-end gypsum product, mainly …
In this study, the effect of sulphonated naphthalene formaldehyde condensate (SNF) and polycarboxylate (PC) superplasticizers on the performance of β-calcium sulphate hemihydrate plaster has been discussed. A considerable improvement in the properties of β-hemihydrate plaster was observed with an increase in …
Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO4·2H2O), hemihydrate (CaSO4·0.5H2O) and anhydrite (CaSO4).
DOI: 10.1016/J.PCRYSGROW.2007.01.002 Corpus ID: 96747728; Calcium sulphate hemihydrate hydration leading to gypsum crystallization @article{Singh2007CalciumSH, title={Calcium sulphate hemihydrate hydration leading to gypsum crystallization}, author={Nakshatra Bahadur Singh and Bernhard Middendorf}, journal={Progress in …
Semantic Scholar extracted view of "Utilization of phosphogypsum for the preparation of α‐calcium sulfate hemihydrate in chloride‐free solution under atmospheric pressure" by Yang Mi et al. Skip to ... Utilization of phosphogypsum to synthesize α-hemihydrate gypsum in H3PO4–H2O solution. Long Chen Lin Yang Jianxin Cao. Materials Science ...
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 rate of the gypsum-hemihydrate transformation is dominantly controlled by temperature, T, ... (Chihuahua, Mexico) is a world geological treasure worth to be preserved. These crystals of up to ...
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. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved …
Alpha high‐strength hemihydrate gypsum (CaSO 4 ·0.5H 2 O, α‐HH) with a large‐size columnar crystal (average size: 135.31 µm, maximum size: 500 µm) is successfully prepared via a NaCl ...
Here we report a facile and cost-effective wet-chemical approach to the synthesis of calcium sulfate hemihydrate nanowires (HH NWs, CaSO4·0.5H2O), and their robust performance in immobilizing water molecules to the crystal lattice of CaSO4 and then separating them from a surfactant-stabilized water-in-oil emulsion (mean droplet size of …
Theoretically, hydrogen would be the better option, because it is only bounded in the water in gypsum and hemihydrate and oxygen is also bounded to sulfur in the sulfate. A new piece of the crystal was stored for a shorter time (around 30 min) at 140 C and prepared in the same way as for the experiments shown in Figure 6a,b, leading to an ...
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 …
The mass loss in the temperature range of 81.6 ℃∼137.1 ℃ is caused by the dehydration of gypsum into hemihydrate gypsum, which is in accordance with ref [40]. As the temperature continues to increase to 297.5 °C, the mass loss reaches 5.80 %. This is the result of the removal of crystal water from hemihydrate gypsum and omongwaite.