The calcination treatment at the temperature of 150 °C, 350 °C, 600 °C, 800 °C with calcination time of 0.5 h, 1 h, 1.5 h, 2 h is used to improve the performance …Web
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Dehydration of PG to β-hemihydrate depends on the calcination temperature and time. • Increasing calcination temperature could accelerate the dehydration of PG. • Phosphorus and fluorine could not be removed by calcination at …Web
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The paper assesses the influence of the calcination temperature of synthetic gypsum binder on the binding properties of innovative gypsum pastes, as well as on masonry and plastering mortars. ... The first intense dehydration of the dihydrate into hemihydrate occurs in the temperature range of 107–170 °C . The transition of the …Web
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A temperature of 150 °C with residence times on the kiln of 1 h and 2 h were found as adequate parameters to obtain considerable β-hemihydrate content with lower energy consumption. View Show ...Web
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The currently commonly used PG pretreatment methods can partially solve the impurity problem, such as using high-temperature calcination to obtain hemihydrate or anhydrous gypsum for use as cement ...Web
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In 1903, Jacobus Henricus van't Hoff and his co-workers gave a transition temperature for the gypsum–hemihydrate reaction of 107 °C and proposed the existence of a soluble anhydrite form in the wrong assumption of a direct dehydration of gypsum without the intermediate hemihydrate step at 93 °C, which was confirmed and revised ...Web
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In the lower temperature range (between 25 and 120 °C), two phases co-exist. The first one is γ-anhydrite and the second can be indexed in the monoclinic system, space group I2 (n° 5) with cell parameters similar to those proposed by Bezou et al. [] for hemihydrate.Between 150 and 300 °C only γ-anhydrite is present and diagrams can be …Web
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The calcination at low temperatures transforms phosphogypsum (PG) waste in a material with binder properties. This study evaluated two parameters of PG calcination: kiln residence time (1 h, 2 h, and 5 h) and temperature (120 °C, 150 °C, and 200 °C). The main objective was to find adequate calcination conditions considering PG …Web
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Calcination in simple words can be described as a process of heating some solid material or a substance in a controlled environment. Usually, in the process, the temperature is also regulated. Win up to scholarship on Aakash BYJU'S JEE/NEET courses with ABNAT Win up to scholarship on Aakash BYJU'S JEE/NEET courses with ABNATWeb
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The hemihydrate gypsum in EMR calcined at 180℃ provides a key dissolution-inhibiting mechanism during the 6 h-12 h phase, thus inhibiting the hydration of C 3 S and C 3 A at this period. ... Low temperature calcination is an appropriate method to pretreat the electrolytic manganese residue (EMR). 180℃ is selected as an optimal …Web
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The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination temperature was able to fully convert the PG to β-hemihydrate SG. Additionally, SG prepared using 180 ºC calcined PG exhibited the highest compressive strength (9.15 MPa).Web
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3.3. Hydration Degree. The effect of different forms of P 2 O 5 on the crystalline water content of hemihydrate phosphogypsum is shown in Figure 4.It can be seen that, in the initial hydration stage, the form soluble P 2 O 5 of H 3 PO 4 and can effectively accelerate the hydration reaction of hemihydrate phosphogypsum, and the …Web
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At room temperature hemihydrate is more soluble in water than gypsum, causing the hemihydrate to dissolve and the gypsum to precipitate. On a pure basis [ pure gypsum] only 18.6 ml of water is required to convert 100 g of hemihydrate to gypsum. ... The kettle calcination temperature was 147° C., operating at a typical continuous …Web
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The results show that the increase in calcination temperature resulted in higher anhydrite content, and CPG showed similar chemical and mineral compositions at high temperatures (500°C–800 °C).Web
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Schaefer et al. [27] calcined untreated PG at 190 °C, 350 °C, 450 °C, 550 °C, and 650 °C to produce β-hemihydrate and anhydrite, respectively, and found that the higher calcination temperature, the better performance and lower solubility of PG will be.Web
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Hemihydrate phosphogypsum (HPG) can be derived from dehydration of PG by low temperature calcination (about 180 °C). The low mechanical strength and poor water resistance of HPG restrict its ...Web
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The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination …Web
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Currently, a large number of studies have reported that FGD gypsum can be converted into hemihydrate gypsum (CaSO 4 ·0.5H 2 O, HH) to broaden its reuse. Based on its process, HH is further divided into two kinds: α-HH and β-HH. α-HH is obtained from the calcination of gypsum in a steam-saturated under increased pressure or using …Web
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FGD-gypsum (flue gas desulfurization), followed by a calcination step. During calcination, calcium sulfate subhydrates (CaSO4 1/2 H2O or CaSO4 2/3 H2O) are formed. This ... phase decomposition of dihydrate to hemihydrate, the temperature inside of the crystal should not increase above the decompositio n temperature in which …Web
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The solubility of gypsum is nearly constant with regard to the temperature, but the solubility of hemihydrate decreases with increasing temperature. Above ~100 °C, hemihydrate becomes less soluble than …Web
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Bumanis et al. [12] found that the higher the calcination temperature, the shorter the time to obtain β-hemihydrate SG. Additionally, when the calcination temperature exceeded 120 °C, the increase in temperature had little effect on the compressive strength of the paste after 14 days (around 14 MPa).Web
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Calcination temperature plays a critical role on morphology and structure of clay. The kaolinite was completely dehydroxylated to become metakaolin at 600 °C, whereas the 2:1 clay minerals were partially dehydroxylated at 700 °C to form high-temperature phases. ... Hemihydrate at 3 wt% delayed the aluminate peak, and more …Web
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In addition, Jin et al. found that the temperature at which dihydrate gypsum is converted into β hemihydrate gypsum is 107–160 °C. Considering the decomposition temperature of soluble fluorine and phosphorus, the calcination modification temperature can be set at about 280 °C for PG.Web
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In order to promote the application of PG, post treatment of hemihydrate phosphogypsum (HPG) by addition of slaked lime (SL) was investigated. As an alkaline additive, SL can neutralize HPG. ... and appearance of gypsum plasters at the calcination temperature of 150 °C and 200 °C were explored. The results showed that at 150 °C, …Web
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The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination temperature was able to fully convert the PG to β-hemihydrate SG. Additionally, SG prepared using 180 ºC calcined PG exhibited the highest compressive strength (9.15 MPa).Web
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The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination …Web
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Gypsum plaster (calcium sulfate hemihydrate) is a material largely employed in civil construction. It is produced by the calcination of the mineral gypsum (calcium sulfate dihydrate) in low temperatures related to other binders. ... [14]. The calcination temperature for gypsum plaster production is low, in the range of 125 °C – 180 °C, it ...Web
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A noticeably higher temperature is thus observed in the conversion of the β-hemihydrate. The maximum temperature is reached well before the hydration process …Web
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The rate of the gypsum-hemihydrate transformation is dominantly controlled by temperature, T, and the water vapour pressure in the reaction environment, p H2O 16,17,18.Web
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The currently commonly used PG pretreatment methods can partially solve the impurity problem, such as using high-temperature calcination to obtain hemihydrate or …Web
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Although PG calcined at elevating temperatures showed significant different properties, there has been no consensus on the calcination temperature for either preparation of hemihydrate gypsum or anhydrite, and a wide scale of previously-reported calcination temperature has been found in the prior studies, ranging from low (100 °C) …Web
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1. Introduction. As a part of the continuing study of gypsum plaster [] 1 the properties of calcium sulfate dihydrate (CaSO 4 · 2H 2 O) and calcium sulfate hemihydrate (CaSO4 · 1/2H 2 O) were studied by differential thermal analysis, thermogravimetry, and differential scanning calorimetric techniques.These investigations were undertaken in order to gain a …Web
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The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination temperature was able to fully convert the PG to β-hemihydrate SG. Additionally, SG prepared using 180 ºC calcined PG exhibited the highest compressive strength (9.15 MPa).Web
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The temperature of the hemihydrate transition for LPdce-08 is 151.7 ... Although there is insufficient data to make a categorical statement that halite reduces the calcination temperature of gypsum, the data confirm anecdotal information regarding the effect of NaCl on the heating of gypsum. Download : Download high-res image (617KB)Web
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Complex kinetic behaviors in the thermal dehydration of CaSO4·2H2O under varying water vapor pressure (p(H2O)) conditions impel researchers in the field of solid-state kinetics to gain a more comprehensive understanding. Both self-generated and atmospheric p(H2O) are responsible for determining the …Web
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Hemihydrate CALCIUM sulphate hemihydrate reacts with water to yield calcium sulphate dihydrate. The rate of this ... temperature of calcination is raised this reaction becomes more rapid. However ...Web
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The first endothermic peak at 150 °C refers to the dehydration of CaSO 4 ·2H 2 O into hemihydrate gypsum. The FGD gypsum begins to dehydrate at about 110 °C and ends at about 190 °C, indicating that the crystal water is completely removed. ... This is also related to the formation of β-HH. When the calcination temperature rises to 220 °C ...Web
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