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.

Research on Affecting Factor of Preparation of Calcium Sulfate Whisker with FGD Gypsum

2014 ◽  
Vol 624 ◽  
pp. 82-85
Author(s):  
Ying Wang ◽  
Dan Jun Tan ◽  
Xiao Li ◽  
Fan Li ◽  
Peng Qi Wang ◽  
...  
Keyword(s):  
Reaction Time ◽  
Reaction Temperature ◽  
Calcium Sulfate ◽  
Ph Value ◽  
Synthesis Method ◽  
Raw Material ◽  
Optimum Conditions ◽  
Fgd Gypsum ◽  
Slurry Concentration ◽  
Calcium Sulfate Whisker

Using FGD gypsum as raw material, calcium sulfate whisker was prepared by hydrothermal synthesis method. Through testing the aspect ratio of calcium sulfate whisker, the effect of reaction temperature, reaction time, desulfurization gypsum slurry concentration and pH value on the growth of calcium sulfate whisker were deeply researched. The optimum conditions for the preparation were that the reaction temperature was 150 °C, reaction time was 270min, the slurry concentration was 10% and the slurry pH value was 6.

Effect of pH on the Preparation of α-Calcium Sulfate Hemihydrate from FGD Gypsum with the Hydrothermal Method

2008 ◽  
Vol 91 (12) ◽  
pp. 3835-3840 ◽  
Author(s):  
Baohong Guan ◽  
Zhuoxian Shen ◽  
Zhongbiao Wu ◽  
Liuchun Yang ◽  
Xianfa Ma
Keyword(s):  
Hydrothermal Method ◽  
Calcium Sulfate ◽  
Effect Of Ph ◽  
Fgd Gypsum ◽  
Calcium Sulfate Hemihydrate

Effect of Organic Diacid Carbon Chain Length on Crystal Morphology of α-Calcium Sulfate Hemihydrate in Preparation from Flue Gas Desulphurization Gypsum

2012 ◽  
Vol 253-255 ◽  
pp. 542-545 ◽  
Author(s):  
Xian Feng Liu ◽  
Jia Hui Peng ◽  
Jian Xin Zhang ◽  
Jin Dong Qu ◽  
Mei Li
Keyword(s):  
Hydrothermal Method ◽  
Flue Gas ◽  
Atmospheric Pressure ◽  
Calcium Sulfate ◽  
Crystal Morphology ◽  
Carbon Chain ◽  
Carbon Chain Length ◽  
Key Technology ◽  
Calcium Sulfate Hemihydrate ◽  
Flue Gas Desulphurization

Modifying crystal morphology was the key technology of the preparation of α-calcium sulfate hemihydrate from flue gas desulphurization gypsum using the hydrothermal method under atmospheric pressure. For exploring crystal modifier, the crystal morphology of α-calcium sulfate hemihydrate in preparation from flue gas desulphurization gypsum with various organic diacid was studied, by polarizing microscope profile observation. The results showed, When the space between two carboxyls was triplicate length of C-C, the organic diacid had the best effect of modifying crystal morphology.

Preparation of Calcium Sulfate Whisker by Hydrothermal Method from Flue Gas Desulfurization (FGD) Gypsum

2012 ◽  
Vol 268-270 ◽  
pp. 823-826 ◽  
Author(s):  
Liu Shuan Yang ◽  
Xiao Wang ◽  
Xin Feng Zhu ◽  
Ling Zhi Du
Keyword(s):  
Hydrothermal Method ◽  
Reaction Temperature ◽  
Flue Gas ◽  
Calcium Sulfate ◽  
Raw Materials ◽  
Flue Gas Desulfurization ◽  
Minor Effect ◽  
Fgd Gypsum ◽  
Excellent Quality ◽  
Calcium Sulfate Whisker

In this paper, utilizing the purified flue gas desulfurization (FGD) gypsum as raw materials to prepare calcium sulfate whisker (CSW) by hydrothermal method, the effects of the dosage of crystal modifier, reaction temperature, pH, etc. on the crystal morphology of CSW were discussed. The results show that the purified FGD gypsum can replace high-quality natural gypsum for the preparation of the CSW with excellent quality. The dosage of crystal modifier (K2SO4) and reaction temperature have a significant effect on the morphology and aspect ratio of CSW, while pH and reaction time have a minor effect. When the dosage of K2SO4 is 3 wt%, pH is adjusted to 2 and the solution is reacted at 130 °C for 60 min, CSW with excellent quality can be obtained.

Preparation of α-calcium sulfate hemihydrate from FGD gypsum in K, Mg-containing concentrated CaCl2 solution under mild conditions

Fuel ◽  
2009 ◽  
Vol 88 (7) ◽  
pp. 1286-1293 ◽  
Author(s):  
Baohong Guan ◽  
Liuchun Yang ◽  
Zhongbiao Wu ◽  
Zhuoxian Shen ◽  
Xianfa Ma ◽  
...  
Keyword(s):  
Calcium Sulfate ◽  
Fgd Gypsum ◽  
Mild Conditions ◽  
Calcium Sulfate Hemihydrate ◽  
Cacl2 Solution

The Kinetics and Mechanism of Formation of Calcium Sulfate Scale Minerals—The Influence of Inhibitors

CORROSION ◽  
1979 ◽  
Vol 35 (7) ◽  
pp. 304-308 ◽  
Author(s):  
GEORGE H. NANCOLLAS ◽  
WESLEY WHITE ◽  
FELIX TSAI ◽  
LARRY MAS LOW
Keyword(s):  
Calcium Sulfate ◽  
Mechanism Of Formation ◽  
Seeded Growth ◽  
Langmuir Adsorption ◽  
Calcium Sulfate Dihydrate ◽  
Calcium Sulfate Scale ◽  
Rate Of Reaction ◽  
Growth Method ◽  
Kinetics Of ◽  
Calcium Sulfate Hemihydrate

Abstract A seeded growth method has been used to study the kinetics of crystallization of calcium sulfate dihydrate at various temperatures and at ionic strengths up to 0.6M. Under all conditions, the rate of reaction is proportional to the square of the relative supersaturation and is controlled by a surface process. The same kinetics are applicable for the growth of calcium sulfate hemihydrate at temperatures above 110 C. The organic phosphonates effectively retard scale formation, and diethylenetriaminepenta (methylenephosphonic acid), when present at a concentration as low as 10−7M, completely inhibits the growth of calicum sulfate hemihydrate at 120 C. By assuming that the inhibitor molecules are adsorbed on growth sites on the surface of the crystals, the inhibition can be interpreted in terms of a simple Langmuir adsorption isotherm.

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.

Influence of Seed Crystal and Modifier on the Morphology of α-calcium Sulfate Hemihydrate Prepared by Salt Solution Method in Pilot Scale

2010 ◽  
Vol 168-170 ◽  
pp. 8-12
Author(s):  
Bao Kong ◽  
Bao Hong Guan ◽  
Liu Chun Yang
Keyword(s):  
Salt Solution ◽  
Calcium Sulfate ◽  
Solution Method ◽  
Pilot Scale ◽  
Seed Crystal ◽  
Flue Gas Desulfurization ◽  
Fgd Gypsum ◽  
Mixed Salts ◽  
Spherical Crystals ◽  
Calcium Sulfate Hemihydrate

Preparation of α-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum is of great value in effectively utilizing the FGD gypsum. This paper focuses on the effect of seed crystal and some modifiers on the morphology of α-HH on a 500-1000 kg/batch setup based on a salt solution method established on the previous work. The pilot tests were carried out in a Ca-Mg-K chloride solution medium at 94 oC (±2 oC) under atmospheric pressure. The results show that a small amount of seeds is advantageous to prepare short-prism α-HH but results in needle-like and spherical crystals in the case of more than 1% addition. The well-shaped α-HH crystals can also be obtained by adding appropriate amounts of crystal modifiers like Fe3+ and the mixed salts of Al3+ and organics.

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