| 摘要 |
Alpha-gypsum hemihydrate is an important building material, which is obtained especially by calcination of calcium sulphate dihydrate, which arises in the desulphurisation of a power station flue gas or in the chemical sector, for example in the manufacture of phosphoric acid. A particularly advantageous calcination process comprises first preparing a dispersion of calcium sulphate dihydrate and aqueous sulphuric acid solution in the presence of sulphuric acid salts and then heating this dispersion, while maintaining a predetermined heating-up rate, to about 373 K together with industrial, dust-free thermal waste, whereupon the solid constituents are then separated off from the aqueous sulphuric acid and dried. Due to the combination of aqueous sulphuric acid solution and sulphuric acid salts, the result of this process is an alpha-gypsum hemihydrate virtually without fractions of anhydrite II, which substantially facilitates the processing thereof. Apart from the negligibly small fraction of anhydrite II, the alpha-gypsum hemihydrate product is distinguished, if magnesium oxide is added, by high fineness and absence of any efflorescence phenomena. <IMAGE>
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