Direct transformation of calcium sulfite to α-calcium sulfate hemihydrate in a concentrated Ca–Mg–Mn chloride solution under atmospheric pressure

Fuel ◽  
2011 ◽  
Vol 90 (1) ◽  
pp. 36-41 ◽  
Author(s):  
Baohong Guan ◽  
Hailu Fu ◽  
Jie Yu ◽  
Guangming Jiang ◽  
Bao Kong ◽  
...  
Keyword(s):  
Atmospheric Pressure ◽  
Calcium Sulfate ◽  
Chloride Solution ◽  
Direct Transformation ◽  
Calcium Sulfite ◽  
Calcium Sulfate Hemihydrate

Direct transformation of FGD gypsum to calcium sulfate hemihydrate whiskers: Preparation, simulations, and process analysis

Particuology ◽  
2015 ◽  
Vol 19 ◽  
pp. 53-59 ◽  
Author(s):  
Miao Miao ◽  
Xin Feng ◽  
Gangling Wang ◽  
Shaomei Cao ◽  
Wen Shi ◽  
...  
Keyword(s):  
Calcium Sulfate ◽  
Process Analysis ◽  
Direct Transformation ◽  
Fgd Gypsum ◽  
Calcium Sulfate Hemihydrate

EFFECT OF WATER VAPOR ON THE FORMATION OF MODIFICATIONS

1965 ◽  
Vol 43 (9) ◽  
pp. 2522-2529 ◽  
Author(s):  
R. A. Kuntze
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Atmospheric Pressure ◽  
Calcium Sulfate ◽  
Water Vapor Pressure ◽  
Exothermic Peak ◽  
Vapor Pressures ◽  
Ambient Water ◽  
Rate Of Heating ◽  
Calcium Sulfate Hemihydrate

The two recognized forms of calcium sulfate hemihydrate can be identified by the position of a relatively small exothermic peak in their differential thermograms. Hemihydrates prepared at various water vapor pressures up to 760 mm Hg were found to produce this exothermic peak in a position which is characteristic for the β-form. These results indicate that α-hemihydrate cannot be made at atmospheric pressure, as was previously suggested on the basis of heat solution measurements. The typical differential thermogram of α-hemihydrate is only obtained with material made by dehydration in solution or by autoclaving. The effect of ambient water vapor pressure on the position of the three peaks that occur in the differential thermogram of CaSO4•2H2O has also been studied. It was found that the incipient temperature of the second endothermic peak, corresponding to the transition of hemihydrate to soluble anhydrite, is displaced independent of the rate of heating from 145 °C to 187 °C with increasing water vapor pressures up to 760 mm Hg. This indicates that, for each temperature, a threshold water vapor pressure exists, above which soluble anhydrite cannot be formed.

The Effect of Process Conditions on the Preparation of α-Calcium Sulfate Hemihydrate from FGD Gypsum Using the Hydrothermal Method under Atmospheric Pressure

2011 ◽  
Vol 250-253 ◽  
pp. 881-889 ◽  
Author(s):  
Xian Feng Liu ◽  
Jia Hui Peng ◽  
Chen Yang Zou ◽  
Leng Bai ◽  
Mei Li
Keyword(s):  
Hydrothermal Method ◽  
Reaction Temperature ◽  
Salt Concentration ◽  
Atmospheric Pressure ◽  
Calcium Sulfate ◽  
Ph Value ◽  
Fgd Gypsum ◽  
Rate Of Reaction ◽  
Percent Conversion ◽  
Calcium Sulfate Hemihydrate

This paper studies the laws of crystal growth, percent conversion and the rate of reaction of α-calcium sulfate hemihydrate from FGD gypsum under different conditions using the hydrothermal method under atmospheric pressure. The crystal morphology was observed by using SEM, polarizing microscope profile, and percent conversion and the rate of reaction were obtained by assaying crystal water content and calculating. The results showed, (1) with the increase of reaction temperature, the dehydration rate increased and the formed α-calcium sulfate hemihydrate crystal had a larger particle size; (2) with the increase of salt concentration or slurry concentration, the formed α-calcium sulfate hemihydrate crystal was smaller, percent conversion and the rate of reaction was nearly unchanged; (3) with the increase of pH value of solution, the rate of reaction increased and percent conversion was nearly unchanged, and with pH value ranging from 5 to 7 the formed α-calcium sulfate hemihydrate crystal was crassitude. In conclusion, the perfect technological parameters were as follows: reaction temperature ranging from 95°C to 100°C, salt concentration ranging from 15% to 20%, slurry concentration ranging from 15% to 20%, pH value ranging from 5 to 7, and reaction time not exceeding 90min.

Modification and Scale-Up Process of Citrogypsum to α-Calcium Sulfate Hemihydrate over Sodium Chloride Solution

2020 ◽  
Vol 990 ◽  
pp. 55-60
Author(s):  
Thanakit Sirimahasal ◽  
Yutthana Kalhong ◽  
Lida Simasatitkul ◽  
Siriporn Pranee ◽  
Samitthichai Seeyangnok
Keyword(s):  
Sodium Chloride ◽  
Calcium Sulfate ◽  
Chloride Solution ◽  
Sodium Chloride Solution ◽  
Batch Reactor ◽  
Scale Up ◽  
Exothermic Peak ◽  
Laboratory Scale ◽  
Coefficient Of Determination ◽  
Calcium Sulfate Hemihydrate

It describes the development of a marketable citrogypsum which is also a by-product of citric acid production from laboratory scale to pilot scale. The modification of b-phase citrogypsum was carried out in different sodium chloride solution at 95oC for 7 hours under atmospheric pressure to α-calcium sulfate hemihydrate (α-CaSO4∙0.5H2O, α-HH). This can be achieved in the laboratory scale experiment. The phase analysis of a citrogypsum was confirmed by XRD technique demonstrated that mostly made up of calcium sulfate dihydrate (CaSO4∙2H2O, DH). The dehydration and phase transformation of citrogypsum to α-HH were conducted by DSC thermograms which were presented two endothermic peaks in the range 150-180oC of citrogypsum and an exothermic peak at 290 to 300oC, resulting that the product being α-HH when the 4M and 5M sodium chloride solutions were used. The outcome products were presented in a plate-like shape of citrogypsum but a hexagonal shape of α-HH. The experiment scaled up for modification of DH up to 100% in a batch reactor at the same condition with the 4M sodium chloride solution. The results showed that α-HH was obtained within 15 to 60 min after that calcium sulfate anhydrous (CaSO4, AH) had been formed. The non-isothermal of DSC was an adapted method to investigate kinetics study of DH to α-HH transformation under the optimum condition with a model fitting dα/dt = -3k (α2) for predicting the process compared to the experiment values. In addition, the coefficient of determination (R2) from estimation and experiment value was 0.9940. Hence, the model equation was completely represent data.

scholarly journals The formation of needlelike .ALPHA.-calcium sulfate hemihydrate from calcium sulfite hemihydrate.

1987 ◽  
pp. 2279-2285 ◽  
Author(s):  
Hiroshi MATSUI ◽  
Kayoko AMITA ◽  
Genzo HASHIZUME ◽  
Gin-ya ADACHI ◽  
Jiro SHIOKAWA
Keyword(s):  
Calcium Sulfate ◽  
Calcium Sulfite ◽  
Calcium Sulfate Hemihydrate
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