The paper assesses the influence of the calcination temperature of synthetic gypsum binder 14 on the binding properties of innovative gypsum pastes as well as on masonry and plastering mortars
If gypsum is heated to at higher temperatures than 150 160 °C the resulting product is anhydrous calcium sulfate The mixture of hemihydrate gypsum pow dry and set rock hard The term plaster is gen erally used to describe the powder generated by calcination of gypsum and the slurry made when mixing with water As the plaster and
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
Studies on the calcination process of PG show that calcination temperature high and low temperatures and time are the most important parameters affecting the conversion of PG into β hemihydrate gypsum or anhydrite [20] [21] Geraldo et al [17] evaluated calcination temperature and kiln residence time of PG and found that increasing residence time and
the time limiting step in these processes is the step of forming the alpha hemihydrate gypsum Even in processes where the dihydrate gypsum slurry is continuously fed into a vessel and alpha hemihydrate gypsum continuously removed from the vessel the slurry must remain in the vessel for a residence time on the order of hours as described above for the full conversion to alpha
With the best calcination temperature of 800 °C gypsum plaster showed a relatively quick setting and maximum strength with a compact microstructure and low hydration degree due to the large
As one of the extensively used inorganic cementitious material hemihydrate gypsum HH CaSO 4 · 2 O has two forms namely β HH and α HH β phase is a dehydration product of calcium sulfate dihydrate DH CaSO 4 ·2H 2 O in dry air at 105 180 °C and has a longer history of application whilst α HH can be produced by wet calcination
The main synthetic materials are α hemihydrate gypsum dihydrate calcium carbonate adsorption materials and composite material Table 4 The preparation of α hemihydrate gypsum α HH is an effective way to realize the high value utilization of FGD gypsum The formation mechanism and crystal structure of α HH are shown in Fig 4 FGD
Gypsum commonly exists in several phases including CaSO 4 ⋅2 H 2 O α CaSO 4 ⋅ H 2 O β CaSO 4 ⋅ H 2 O Ⅰ CaSO 4 Ⅱ CaSO 4 and Ⅲ CaSO at room temperature is in the stable form of CaSO 4 ⋅2 H 2 O Various treatment methods [11] are nowadays employed to remove crystalline water resulting in hemihydrate and anhydrite for
Method and apparatus for calcining gypsum in a kettle 10 in which the calcined mass is fluidized Heat for the calcination is supplied by heating rods 46 which are immersed in said bed Said heating rods 46 supply about 1 British Thermal Unit Btu of heat per minute per square inch of surface area of rod Heat is also supplied to the calcined mass by a hot gas produced by
Table 3 presents the chemical composition of CPG at different calcination temperatures CPG mainly consists of CaO and SO 3 and contains more than 90 wt% hemihydrate or anhydrite which is higher
The mixture of hemihydrate gypsum powder with water forms a slurry or paste that will dry and set rock hard The term plaster is generally used to describe the powder generated by calcination of gypsum and the slurry made when mixing with water As the plaster and water mixture dries water will chemically recombine with the hemihydrate gypsum
α hemihydrate gypsum resulting in larger crystal diam eters and coarser particle sizes of α hemihydrate gypsum Phosphogypsum can also be subjected to low temperature calcination 110 170 °C to produce β hemihydrate gyp sum However the calcination temperature is insufficient to eliminate impurities resulting in poor mechanical
A novel modified phosphorus β hemihydrate gypsum MPG cementing material was developed to solidify lead contaminated soil The solidification effects of lead in the contaminated soil with MPG and Portland cement PC as curing agent were contrasted by the unconfined compressive strength UCS pH and leaching toxicity of solidified soil The
using high temperature calcination to obtain hemihydrate or anhydrous gypsum for use as cement and slag com posite cementitious materials 10 11 ; using calcium hydroxide to neutralize the acid in
wallboard gypsum must be partially dehydrated or calcined to produce calcium sulfate hemihydrate CaSO4 ½H 2O commonly called stucco A flow diagram for a typical gypsum process producing both crude and finished gypsum products is shown in Figure 1 In this process gypsum is crushed dried ground and calcined
The results show that the obtained hemihydrate gypsum mixing with water can prepare high performance building gypsum after the FGD gypsum adding 3 5 wt% of CaO is calcined at 160 220 °C for 2 h is closely connected to its calcination temperature but systematic studies which relate those features to mechanical properties and
The inlet temperature at the hot gas duct of this mill is usually about 600 °C while the gas tempera ture after classifier is set to about 150 160 °C The lengthens the setting time of the b hemihydrate produced in the gypsum kettle to about 12 20 min utes without the addition of retarders
The α hemihydrate hydration results in a high dihydrate formation; therefore this type of gypsum is applied in conditions where more significant strengths are necessary sculptures and sanitaryware casing [36] [37] β Hemihydrate is obtained through the dry calcination of gypsum in the range of 120 °C 180 °C and it is an easier
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory over bassanite hemihydrate; CaSO4• to gypsum CaSO4
The calcination of phosphogypsum PG was employed to produce gypsum plaster to achieve its recovery and utilization Although previous studies have indicated the possibility of producing hemihydrate and anhydrous gypsum the influence
High strength gypsum is the recognized designation for α hemihydrate gypsum often referred to as α HH CaSO 4 · 2 O which is a cementitious material with low water requirement and high strength [8] The strength of α HH is generally between 25 and 50 N/mm 2 which is three times that of ordinary building plaster and has superior working performance α
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