FGD GYPSUM - A PROMISING INDUSTRIAL BY-PRODUCT FOR THE GREEK CEMENT INDUSTRY

摘要

The majority of cement plants in Greece mainly use natural gypsum to prevent rapid cement setting. The partial or total replacement of gypsum by materials, which contain calcium sulphate, has been instigated by two facts. Firstly, the increasing availability of low-cost by-products containing calcium sulphate and secondly, the prospect of the gypsum quarries to mine, in the near future, a rock that is a mixture of gypsum and anhydrite. FGD gypsum, a waste material of the desulphurisation process in coal burning power plants, to convert SO_3 content of flue gases into gypsum, is an important alternative source of chemical gypsum. The aim of this paper is to discuss results from laboratory and industrial scale trials, where calcium sulphate bearing materials (CSBM) such as natural gypsum, anhydrite and FGD gypsum have been used in various proportions in the cement production. At the same time, a hydration study of cements with FGD is presented. The addition of FGD gypsum increases setting time without affecting the compressive strength profile. The degree of dehydration of the dihydrated calcium sulphate regulates setting and strength performance of the cement partially replaced with either anhydrite or FGD gypsum.