Review of Global Gypsum Conference & Exhibition 2019
Three technologies currently exist for the production of alpha hemihydrate gypsum from phosphogypsum: the autoclave process, the hydrothermal process and the normal pressure salt process, but each has its own disadvantages, including high energy costs, low product strength and large amounts of waste water. Liyu Yang presented an …
Crystals | Free Full-Text | Formation of α-Hemihydrate …
Similar results can be achieved by recrystallization from gypsum slurry around 100 °C in an autoclave or under a water steam atmosphere. However, in contrast, the recrystallization process here leads to the formation of a larger, needle-like morphology and sometimes branched α-hemihydrate crystals. ... The formed product is called alpha ...
Preparation of α-hemihydrate gypsum from phosphogypsum
Preparation of α-hemihydrate is one of the feasible approaches for large-scale consumption of PG. The production process of α-hemihydrate includes …
Transformation pathways from calcium sulfite to α
Titanium gypsum (TG) is rarely used to produce α-hemihydrate gypsum (α-HH) because of its poor crystallinity and high impurity and moisture contents. Here, a method is proposed to prepare α - HH by adjusting the reaction temperature, CaCl 2 solution concentration and maleic acid dosage based on acid leaching and heat-treated TG as …
Calcining processes for natural and synthetic gypsum
With systems such as mill calcining systems for combined grinding and calcining, the rotary kiln, the kettle, and the rotary tubular calciner, as well as continuous autoclaves for the production of alpha hemihydrate, Grenzebach supports its customers so they can optimally process gypsum to ensure that the finished product has the desired qualities.
Autoclave‐Free Formation of α‐Hemihydrate Gypsum
Under optimal working conditions the quality of the formed α-hemihydrate gypsum is similar to that of a material produced in an autoclave. Flue gas gypsum …
gypsum autoclave – Industrial Boiler
Investigations were carried out to produce an autoclaved gypsum plaster (α-hemihydrate) by heating the naturally occurring selenite and by-product phosphogypsum under steam pressure in an autoclave. Autoclave (Alpha Hemihydrate) – Gypmak Autoclave, alpha hemihyrate, alpha plaster, alpha plaster plant manufacturer, alpha …
Preparation of α‐Calcium Sulfate Hemihydrate from Calcium
For the first time, α-calcium sulfate hemihydrate (α-HH) was successfully prepared from calcium sulfate dihydrate (DH) in methanol–water solution under atmospheric pressure. The effect of methanol concentrations (40–73 mol%) on the transition from DH to α-HH were investigated at temperatures (60°–75°C) within a reaction time of 36 h.
Materials | Free Full-Text | Experimental Study and Mechanism
Flue-gas desulphurization (FGD) gypsum is a highly prevalent industrial by-product worldwide, which can be an excellent alternative to natural gypsum due to its high content of CaSO4·2H2O. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved …
Crystallization kinetics of large-sized columnar α-hemihydrate gypsum
In order to utilize the spent CaCl 2 waste from soda plants, in this work a novel process was proposed to directly produce higher strength α-gypsum by the following reaction of CaCl 2 and Al 2 (SO 4) 3 without autoclave equipment at atmospheric conditions: 3 C a C l 2 + Al 2 SO 4 3 + 1.5 H 2 O → Δ 3 C a S O 4 ∙ 0.5 H 2 O + 2 A l C l …
Gypsum hydration: a theoretical and experimental study
Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in two formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α-hemihydrate is too ...
Preparation of α-High-Strength Hemihydrate from Flue Gas
of gypsum binders (α-HH) in all mineral binders is also less than 5% in China compared with 25−27% in Germany and 22% in the United States. 8 Currently, among the main
Crystallization kinetics of large-sized columnar α-hemihydrate gypsum
In order to utilize the spent CaCl 2 waste from soda plants, in this work a novel process was proposed to directly produce higher strength α-gypsum by the following reaction of CaCl 2 and Al 2 (SO 4) 3 without autoclave equipment at atmospheric conditions: (1) 3 C a C l 2 + Al 2 SO 4 3 + 1.5 H 2 O → Δ 3 C a S O 4 ∙ 0.5 H 2 O + 2 A l …
Studies on the preparation of calcium sulphate hemihydrate by an
To enable further work to be carried out on the hydration of hemihydrate plasters, materials purer than the available commercial plasters and with reproducible properties were required. As a first stage in the attempted preparation of such materials, the process variables in the autoclave dehydration of gypsum were investigated. Methods …
Effect of modifiers on crystalizing habit and
α-Hemihydrate gypsum (α-HH) is known as high strength gypsum, the strength of α-HHs is three times larger than that of building gypsum, in addition, α-HH has good working performance, environmental performance and biological performance[7]. ... Effects of the impurities oil the habit of gypsum in wet-process phosphoric acid. Ind. …
during the Dehydration Process
The obtained product is -hemihydrate ( -HH), which crystallizes in small crystals (Figure 1b). Another way is a recrystallization process at around 100 C in an …
Synthesis of α-hemihydrate gypsum from cleaner phosphogypsum
Titanium gypsum (TG) is rarely used to produce α-hemihydrate gypsum (α-HH) because of its poor crystallinity and high impurity and moisture contents. Here, a …
The Mechanism of the First Hydration-Dehydration Cycle of
The chemical composition of alpha hemihydrate (α-HH) from the steam autoclave process and beta hemihydrate (β-HH) were determined by XRD as shown in Table 1. In more detail, hemihydrate was added to water to perform the hydration reaction to obtain dihydrate, and then, the formed dihydrate was crushed and calcinated back to beta …
Effect of pH on the Preparation of α‐Calcium Sulfate Hemihydrate …
The initial pH values of the suspensions were adjusted from 1.2 to 8.0 to explore the influence of pH on the dehydration process and the product characteristics. The results showed that α-HH crystal was the only dehydration product …
Effect of maleic acid and pH on the preparation of α
Phosphogypsum (PG) is a by-product of the wet-process phosphoric acid process, which causes serious environmental issues. In this work, PG was taken as raw material to prepare α-calcium sulfate hemihydrate (α-CSH) at atmospheric pressure using Mg(NO3)2 solution, which is an environmentally friendly chlorine-free salt solution. The …
α or β?-hemihydrates transformed from dihydrate
α-and β-hemihydrate calcium sulfate (HH), the most important calcium sulfate phases, are usually achieved by autoclave hydrothermal reaction and calcination in air, respectively. Herein, we report an investigation on preparation of HH from dihydrate calcium sulfate(DH) in a salt-mediated glycerol-water solution.
Preparation of α-calcium sulfate hemihydrate from
Using solar energy to dehydrate gypsum to produce β-hemihydrate is one way to improve the carbon footprint 13,14 . Alternatively, α-hemihydrate is produced from gypsum using an autoclave process ...
Preparation of alpha-calcium sulfate hemihydrate from FGD gypsum …
This work develops a new class of salt solution method to prepare alpha-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum in trace K 2 SO 4-contained 4.0 M Ca(NO 3) 2 aqueous solution at 95 °C under atmospheric pressure. The driving force for the phase transition is provided by the concentrated Ca(NO 3) 2 …
Formation of α-Hemihydrate Inside of a Gypsum …
Similar results can be achieved by recrystallization from gypsum slurry around 100 °C in an autoclave or under a water steam atmosphere. However, in contrast, the recrystallization process...
Gypsum autoclaves from Maschinenbau SCHOLZ & Co. KG
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Influence of α-Calcium Sulfate Hemihydrate on Setting, …
1. Introduction. Gypsum is a material in which the amount of water of crystallization varies with its surrounding conditions, such as temperature or humidity, and can be classified into three groups, namely, calcium sulfate anhydrite (CaSO 4), calcium sulfate hemihydrate (CaSO 4 ∙1/2H 2 O), and calcium sulfate dihydrate (CaSO 4 ∙2H 2 …
Effects of crystal habit modifiers on the morphology of calcium …
BACKGROUND. This work deals with the effect of several additives on the morphology of calcium sulfate dihydrate (DH) crystals, produced by reactive crystallization involving strong CaCl 2 –HCl solutions. Experiments were conducted at 40 °C under various conditions, namely homogeneous and seeded (heterogeneous) …
Structural characteristic and formation mechanism of hemihydrate
The purified FGD gypsum was mixed with distilled water in a ball mill at a rate of 300 rpm for 4 h. Next, the slurry was placed in a double-walled jacket autoclave. Distilled water was added to ensure a solid to liquid ratio of 1:20–1:30, while 0.01 M H 2 SO 4 and 1.5 wt% CuCl 2 were added to the slurry.
Exam 2
- gypsum begins in nature as calcium sulfate dihydrate (CaSo4. 2 H2O) - when it is heated to 45 degrees Celcius in a procedure called calcinations the calcium sulfate dihydrate loses 3/4 of its water content and become …
Experimental Study and Mechanism Analysis of Preparation of α …
Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the attachment water of the mixture of FGD gypsum and crystal modifiers was approximately 18%, and the pH value was approximately 6.0.