A method for the calcination of powdery or fine-particled plaster, comprising two steps: the plaster is subjected to a flash-calcination in a calcinator and the hot plaster is post-calcinated in a reaction vessel. Post-calcination is carried out in the reaction vessel by adding humid gas, said reaction vessel not being heated. The postcalcination takes place over a long period of time, that is at least 10 times, preferably 50-100 times longer than the amount of time taken for flash calcination. Calcination takes place without expending additional energy, and the remaining dihydrate produced during the flash calcination is also transformed into semi-hydrate and undesired anhydrite fractions are reduced. The method can ensure consistency in the product quality and also increase product quality. The temperature in the upstream calcinator can be lowered thus saving more energy. The method can also be used to accelerate the ageing of calcinated plaster.

Wasted gypsum boards are crushed and calcined to gypsum granular solid, and the gypsum granular solid is mixed with water to form gypsum slurry. Gypsum particles are deposited from the gypsum slurry in a crystallization tank. Heated steam is blown into the gypsum slurry at a height from surface of the gypsum slurry and down to upper ? of the gypsum slurry to heat the gypsum slurry and to eliminate foam on the gypsum slurry.

Gypsum granular solid obtained by crushing wasted gypsum boards is calcined and converted to hemihydrate and/or anhydrous type III gypsum. The gypsum granular solid is fed by a feeding device from a feed port into a fluidized-bed of a calcining apparatus. The gypsum granular solid after calcination is discharged by a discharging device from a discharge port of the fluidized-bed. The amount of the gypsum granular solid in the fluidized-bed is maintained within a predetermined range by controlling the feeding device and the discharging device. The generation of anhydrous type II gypsum is reduced, and the calcining apparatus can be operated stationarily.

A composition of matter is provided, including anhydrite calcium sulfate whiskers having a mean aspect ratio of at least 30. Another composition of matter is provided, including alpha-derived anhydrite calcium sulfate whiskers. Yet another composition of matter is provided, including fine alpha particle-derived anhydrite calcium sulfate whiskers.

The present invention relates to a new method for producing a calcium sulphate hemihydrate with unique properties for use for therapeutic applications in the cosmetic or pharmaceutical industry. Calcium sulphate hemihydrate is a biocompatible and biodegradable inorganic substance and thus suitable as a carrier in pharmaceutical compositions, e.g. a controlled release composition, containing at least one pharmaceutically active ingredient.

A calcined gypsum treatment apparatus has an agitating type of cooler provided with a cooling region for cooling the calcined gypsum, and a moisture supplying device for incorporating moisture into the calcined gypsum. The moisture supplying device includes a humid gas-feeding port which introduces humid gas including moisture or steam, directly into the cooling region. The calcined gypsum is introduced through a calcined gypsum introduction port into the cooling region, and the moisture is incorporated into the calcined gypsum to modify the calcined gypsum. The humid gas-feeding port is positioned in vicinity to the calcined gypsum introduction port so as to allow the spouted or delivered flow of the humid gas to be brought into contact with the calcined gypsum immediately after introduced into the cooling region.

The present invention discloses a method for producing the alpha-calcium sulfate hemihydrate bone graft, which comprises the following steps: mixing calcium sulfate dihydrate and deionized water to produce calcium sulfate dihydrate paste; stirring and heating the calcium sulfate dihydrate paste at least 160 C. within 100-350 psi to produce the conversion calcium sulfate hemihydrate, filtering the conversion calcium sulfate hemihydrate with high temperature to produce the filtered calcium sulfate hemihydrate, and washing the filtered calcium sulfate hemihydrate by absolute alcohol to get the alpha-calcium sulfate hemihydrate bone graft. The present invention does not use any catalyst, possesses a high purity, high mechanical strength, and good biocompatibility, facilitates bone growth and angiogenesis, requires only 31 C., the highest temperature, during the curing process. It makes the present invention more secure in the biomedical applications.

Provided is a method for producing phosphoric acid and at the same time obtaining alpha-hemihydrate gypsum including: adding a phosphate rock powder and a part of dilute sulfuric acid into an extraction tank, carrying out an extraction reaction on same, separating a clear liquid from the obtained mixed slurry, sending the clear liquid, as a finished product phosphoric acid, into an acid storeroom, and transferring a separated solid, together with the rest mixed slurry, into a crystal transformation tank; and adding sulfuric acid and a crystal transformation agent into the crystal transformation tank, carrying out a crystal transformation reaction for 1.5-7.5 h at 60? C.-130? C., and solid-liquid separating the obtained mixed acid slurry, wherein the solid can be dried into a gypsum powder, or may be not subjected to a drying step and made into gypsum products such as gypsum boards, gypsum building blocks and gypsum members by directly adding water.

A method for preparing -calcium sulfate hemihydrate with calcium sulfate dihydrate includes steps of: uniformly mixing the calcium sulfate dihydrate with an additive solution, and obtaining a mixture, wherein weight percentages of the calcium sulfate dihydrate and the additive solution in the mixture are respectively 90.00-95.00% and 5.00-10.00%, and the additive solution contains water, inorganic salt, organic salt, organic acid, surfactant, and seed crystal; rising a temperature of the mixture to 130-150 C., keeping for 20-120 minutes, and the calcium sulfate dihydrate in the mixture transforming to the -calcium sulfate hemihydrate; drying the mixture after reaction at 105-160 C., and thereafter obtaining -calcium sulfate hemihydrate product. The used calcium sulfate dihydrate can be natural raw materials and industrial by-products. The industrial by-products can be directly applied. Through utilizing characteristics of the industrial by-products, a dehydration reaction time and a drying time are shortened, and a product quality is obviously increased.

The present disclosure relates to no fiber calcined gypsum and methods of making the same using a multi-stage (typically two-stage) calcination process. The first stage is a high temperature calcination and nucleation stage. The second stage is a lower temperature calcination and crystal growth stage which produces product slurry containing calcined gypsum particles having large, acicular calcined gypsum crystal morphology for use in making gypsum fiberboard.