Abstract: The process for preparing calcium sulfate anhydrite II by heating a flowable powder of flue gas gypsum moistened with less than 20% by weight, and preferably with from 7 to 17% by weight, of diluted sulfuric acid, wherein the sulfuric acid content is from 0.5 to 7% by weight, and preferably 1 to 3% by weight of sulfuric acid, based on the total mixture, is carried out by that the total mixture is direct-fired or is rapidly heated with indirect heat exchangers having relatively high wall temperatures whereby it is heated at temperatures of from 80.degree. C. to 190.degree. C. and releases the water adherent from the diluted sulfuric acid as well as two moles of water of crystallization, and then the virtually anhydrous product is annealed at temperatures of from 80.degree. C. to 190.degree. C. for 0.3 to 24 hours.

Abstract: A process for producing dry flue gas gypsum substantially free of hemihydrate and anhydrous calcium sulfate comprises drying wet flue gas gypsum, typically having a free water content of about 4-12% by weight, in direct contact with a partial stream withdrawn from a primary stream of a dry dedusted flue gas. Flue gas gypsum produced in a wet desulfuration stage is fed to contact the partial stream and is separated from this partial stream and removed as dried flue gas gypsum. Remaining superfine flue gas gypsum is then fed to the intake side, or to the delivery side of a booster blower arranged upstream of the flue gas desulfuration device along with the partial flue gas stream discharged from the drying stage, and the superfine particulate flue gas gypsum is conducted from the booster blower into the flue gas desulfurizing device to serve as seed crystals for additional production of gypsum therein.

Abstract: Pelletized calcium sulfate is prepared from finely divided, natural or synthetic calcium sulfate, wherein the particle size of the finely divided calcium sulfate is at least about 90 per cent by weight less than 200 .mu.m, there being no particles larger than 500 .mu.m, and wherein the finely divided calcium sulfate has a free water content of from about 0.5 to about 4 per cent by weight, by pressing the finely divided calcium sulfate in the presence of water with a roll press using a surface pressure of 1 to 5 Mp per cm roller length.

Abstract: Calcium sulphate produced by reacting crude phosphate with sulphuric acid is washed with aqueous solutions of condensed and complex aluminium fluorides of the general formulae MeAlF.sub.4, Me.sub.2 AlF.sub.5 and Me.sub.5 Al.sub.3 F.sub.14 as well as AlF.sub.3.nH.sub.2 O, in which Me represents an alkali metal, ammonium or thallium-I ion and n is a number between 1 and 9.

Abstract: A multi-layered gypsum board for construction purposes in which a mixture of gypsum, water and fibers provide the center or core of the board, and a composite coating of a fiberglass layer and a layer of fiberglass fleece covers one of the major surfaces of the core, with the fiberglass layer being embedded into the mixture and plaster favorably adhering to the outer surface of the fiberglass fleece layer. The other major surface of the core may be covered with a similar coating, or a layer, for example, of pasteboard.