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The modified hydrothermal method for the preparation of the alpha hemihydrate calcium sulphate was applied for the dehydration
of gypsum as a product of the flue gas desulphurization process with the gypsum/acid solution mixing ratios 0.125,
0.250, 0.500 and 0.750 g/cm3. The obtained products were investigated by IR, DTA and microscopic analysis. T...
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Phosphoanhydrite was obtained by processing dihydrate phosphogypsum generated during phosphoric acid production at Joint Stock Company (JSC), Lifosa (Lithuania). The influence on the properties of phosphoanhydrite of the treatment process parameters was determined, including: the conditions of phosphogypsum neutralisation in the lime suspension, te...
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... Several researchers investigated the effects of several factors on the physical properties of dental gypsum, such as synthesis methods (Akinnifesi & Ogunbodede, 2012), setting time (Imelda et al., 2020), additives (Azer et al., 2008), and the amount of silica oxides in the material (O'Brien, 2022). Kostic-Pulek et al. (2005) modified the hydrothermal method for the preparation of the alpha-hemihydrate calcium sulfate with the FGD gypsum and acid solution ratios of 0. 125, 0. 250, 0. 500, and 0. 750 g/ cm 3 . They found that the mixing solution ratios of 0. 125-0. ...
... 500 g/ cm 3 had both alpha and beta hemihydrate forms. They concluded that increasing the mixing solution ratios increased the fraction of the alpha form in the final product as well as the reaction rate and the average lengths of the alpha hemihydrate single crystals (Kostic-Pulek et al., 2005). ...
... The FGD gypsum was first heated from room temperature to 120 °C, and the temperature was gradually increased to 165°C. This process took 2 h and 30 min (modified from Kostic-Pulek et al., 2005;Panpa, 2002). The resultant powder was intended to be used as dental plaster gypsum. ...
FGD gypsum, a byproduct of coal-fired power plants, is readily available and relatively inexpensive, which makes it an ideal material for a variety of applications. This study considered the use of FGD gypsum as a substitute for natural gypsum in dental materials. The goal of this research was to investigate how acid treatment time, particle size, and the synthesis method impact the physical and mechanical properties of dental materials to be used in a dental study model for training in dental sciences, and for casting a gypsum model after the removal of the impression material from the patient's mouth. The study used various sulfuric acid treatment times (15, 30, and 60 min), particle sizes (less than 0.1 mm, 0.1-0.35 mm, and 0.4-0.45 mm), and synthesis methods (Method A for dental plaster and Method B for dental stone). From the results, an acid treatment time of 15 min was sufficient for removing impurities from the FGD gypsum while enhancing the compressive strength. The smaller particles provided higher compressive strength than the larger particles. FGD gypsum became lighter in color when treated with sulfuric acid, and the crystal structure had a rough and porous surface. The synthesis methods had a significant influence on the physical properties of dental gypsum. The increased alpha calcium sulfate hemihydrate (α-HH) phase content resulted in improved compressive strength. The gypsum synthesized using Method B exhibited the highest compressive strength due to the presence of the α-HH phase of 65.9%. While gypsum synthesized using Method A contained a α-HH phase of 58.9%. For further study, once the suitable conditions for synthesizing gypsum that meet the compressive strength requirements of the ISO standard for dental materials are achieved, there will be ongoing research and development to improve various properties. Additionally, practical applications will be considered, such as using it in conjunction with modern techniques such as 3D printing instead of traditional die-casting methods.
... βcalcium sulphate hemihydrate (β-CaSO4•0.5H2O) or calcium sulphate (anhydrite, CaSO4). Manufacturing and utilization of α-CaSO4•0.5H2O is widely investigated [23][24][25][26]. However, little works are focused on β-CaSO4•0.5H2O ...
Flue gas desulfurization gypsum (FGD gypsum) is obtained from the desulphurization of combustion gases in fossil fuel power plants. FGD gypsum can be used to produce anhydrite binder. The effect of three independent variables such as the calcination temperature of FGD gypsum (500-800 oC), the hydration time (3-28 days) and the amount of activator (0-2 %) on the compressive strength of anhydrite binder were studied. K2SO4 and Na2SO4 were used as activators. The compressive strength of anhydrite binder was evaluated using a full factorial design. The multiple linear regression models were developed to correlate the significant variables to the compressive strength of anhydrite binder. The experimental results and statistical analysis showed that the hydration time had the biggest impact on the compressive strength of anhydrite binder using K2SO4 and Na2SO4. K2SO4 made a greater influence on the compressive strength than Na2SO4. The results of modeling indicated that the individual variables had a larger effect on the compressive strength of anhydrite binder than their interaction. The mean absolute percentage error between experimental and calculated values of compressive strength was less than 10 %.
... [1][2][3] The common methods for producing α-HH from DH include commercialized autoclave technology 4 and salt solution process. 2,[5][6][7] The former that involves heating DH in an autoclave at elevated temperatures (above 120°C) and pressures, is energy-intensive, whereas the latter requires a high concentration of salt solutions that can result in serious equipment corrosion. An alternative approach to preparing α-HH from DH in glycerol-water solutions under mild conditions has been suggested. ...
Here we reported a method to simultaneously control the particle size and morphology of α‐CaSO4·1/2H2O (α‐HH) prepared from flue gas desulfurization gypsum by adjusting the succinic acid concentration and glycerol content under mild conditions. Succinic acid controlled the crystal morphology by adsorption onto α‐HH surfaces, and glycerol controlled the crystal particle size, in which an increase in the maximal relative supersaturation (Smax) and nucleation rate of α‐HH was hypothesized to cause the change in α‐HH particle size. Then, based on the method, α‐HH with different particle sizes but with almost the same morphology was prepared, and the influence of the crystal particle size on the mechanical strength of the α‐HH pastes was explored. With decreasing α‐HH particle size from about 26 to 5 μm, the dry compressive strength of the pastes made from the α‐HH decreased remarkably from 68.02 to 34.85 MPa, which was ascribed to an increase in the internal porosity of the pastes.
... Methods for preparing a-HH from DH mainly include commercialized autoclave technology [8], salt solution process [5,9,10] and alcohol-water solution [11][12][13]. The autoclave technology that involves heating the DH at elevated temperatures (above 120°C) and under certain pressures, is energy intensive; whereas the salt solution process that requires high-concentration salt solutions can lead to serious equipment corrosion. ...
Huge amount of flue gas desulphurization (FGD) gypsum not only occupies the farmland but also causes severe pollution to the surrounding environment. The most effective way to achieve a high-value utilization of FGD gypsum is to prepare short columnar α-calcium sulfate hemihydrate (α-HH) since short columnar crystals show better mechanical strength than needle-like ones. Here, malic acid, a prolific, inexpensive and environment-friendly modifier was explored for the first time to effectively tune the crystal morphology of α-HH prepared from FGD gypsum in glycerol-water-NaCl solutions. When the concentration of malic acid reached 18.54 × 10-4 mol/kg, α-HH crystals with an average aspect (length-to-diameter) ratio of 1.9 (compared to 29.4 in the absence of malic acid) were prepared. The selective complexation of malic acid with Ca active sites on different α-HH crystal planes played a dominant role in the α-HH crystal morphology transformation, which was then explained by the surface broken bonds theory for the first time. The broken bond number per active Ca atom (Nbper Ca) and broken bond density of Ca atoms (DbCa) on the (2 0 4) end plane were larger than those on the (0 2 0) or (2 0 0) side planes. Therefore, the (2 0 4) end plane was more reactive with organics, resulting in the preferential adsorption of malic acid on the end planes, which reduced the specific surface energy of (2 0 4) and led to an increased exposure of this plane and a decreased exposure of (0 2 0) or (2 0 0) side planes in the final α-HH crystals. Consequently, using malic acid as modifier, the α-HH crystal gradually transformed from a needle-like shape to a short columnar one. This work provided important insights into and perspectives for the selection of crystal modifiers and explanation of the mechanism during the preparation of calcium-containing crystals with controllable morphology.
... Also, -CaSO 4 0.5H 2 O was obtained from sulphogypsumin in 3M NaCl solution (at temperature of boiling and atmospheric pressure) (Kostić-Pulek et al. 1996). By treatment of sulphogypsum in 20% H 2 SO 4 solution (at ambient conditions) the mixture of -CaSO 4 0.5H 2 O and -CaSO 4 0.5H 2 O was formed (Kostić-Pulek et al. 2005). ...
Abstract: The possibilities of the application of waste gypsum (citrogypsum,
nitrogyosum and sulphogypsum), fly ash and bottom ash in construction: for
production of gypsum binders (-calcium sulphate hemihydrate, -calcium
sulphata hemihydrate and -anhydrite), for obtaining construction products
(bricks and blocks) and as component materials for road layers were presented in
this work. Also, the possibilities of the application of sulphogypsum (or FGD
gypsum) for solidification and stabilization of fly ash were presented. The
obtained results could have great importance in both ecological and economic
views (elimination of important pollutants of water, air and soil, replacement of
natural by waste materials, reduction of waste disposal cost).
Key words: waste gypsum, fly ash, bottom ash, gypsum binders, construction
Apstrakt: U ovom radu su prikazane mogućnosti primene otpadnog gipsa
(citrogipsa, nitrogipsa i sulfogipsa), pepela i šljake u građevinarstvu i to: za
proizvodnju gipsnih veziva (-poluhidrata kalcijum sulfata, -poluhidrata
calcijum sulfata i -anhidrita), za dobijanje gradjevinskih proizvoda (cigala i
blokova) i kao materijala za izgradnju gornjih i donjih slojeva puteva. Takođe su
prikazane i mogućnosti primene sulfogipsa za solidifikaciju i stabilizaciju pepela.
Dobijeni rezultati mogli bi da imaju bitan značaj, kako sa ekološkog gledišta
(uklanjanje značajnih zagađivača životne sredine: voda, vazduha i tla) tako i sa
ekonomskog gledišta (zamena prirodnih sirovina otpadnim materijalom i
smanjenje troškova skladištenja otpadnog materijala).
Ključne reči: otpadni gips, pepeo, šljaka, gipsna veziva, građevinarstvo
... Preparation of a-HH from DH has been widely investigated [10,11]. Though the autoclave method [12] proceeding at elevated temperature and pressure has been commercially adopted, an autoclave-free method [13][14][15] under atmospheric pressure has drawn attention since 1990s. ...
Massive quantities of sulfite-rich flue gas desulfurization (FGD) scrubber sludge have been generated by coal burning power plants. Utilization of the sulfite-rich sludge for preparing α-calcium sulfate hemihydrate (α-HH), an important kind of cementitious material, is of particular interest to electric utilities and environmental preservation. In the experiment, calcium sulfite hemihydrate was directly transformed to α-HH without the occurrence of calcium sulfate dihydrate (DH). The transformation was performed in a concentrated CaCl2 solution containing Mg2+ and Mn2+ at 95 °C, atmospheric pressure and low pH. The oxidation of calcium sulfite and the subsequent crystallization of α-HH constitute the whole conversion, during which the oxidation turns out to be the rate controlling step. Solid solution comprised of calcium sulfite hemihydrate and calcium sulfate was found to coexist with α-HH in the suspension. Calcium sulfate increases and calcium sulfite decreases spontaneously until the solid solution disappears. Thus, it is a potential alternative to utilize sulfite-rich FGD scrubber sludge for the direct preparation of α-HH.
The massive accumulation of flue gas desulfurization (FGD) gypsum produced in the wet limestone-gypsum flue gas desulfurization process not only encroaches on lands but also causes serious environmental pollution. The preparation of α-hemihydrate gypsum (α-HH) is an important way to achieve high-value utilization of FGD gypsum. Although the glycerol-water solution approach can be used to produce α-HH from FGD gypsum under mild conditions, the transition is kinetically unfavorable in the mixed solution. Here, an easy pretreatment was used to activate FGD gypsum by calcination and hydration to readily complete the transition. The pretreatment deteriorated the crystallinity of FGD gypsum and caused it to form small irregular flaky crystals, which dramatically increased the specific surface area. Additionally, most of the organics adsorbed onto FGD gypsum surfaces were removed after pretreatment. The poor crystallinity, increased specific surface area, and elimination of organics adsorbed onto crystal surfaces effectively improved the conversion activity of FGD gypsum, thereby promoting dihydrate gypsum (DH) dissolution and α-HH nucleation. Overall, the phase transition of FGD gypsum to α-HH is facilitated.
