PRODUCTION, PROPERTIES AND APPLICATION OF CALCIUM-CARBONATE POWDERS .2. PRODUCTION OF CALCIUM-CARBONATE FROM CALCIUM-SULFATE RAW-MATERIALS

The reaction of gypsum or anhydrite with ammonium carbonate was for a long time the basis of the production of the fertilyzer ammonium sulph ate. Up to the beginning of the nineties in the Leuna-Werken ernomous quantities of this fertilyzer were produced. The by-product lime mud ( Leunakalk) was used as lime fertilyzer or repelled. Therefore the chem ical composition and the particle size and shape were of minor importa nce. Only when it was noticed, that the Leunakalk was a potential raw material for many applications, the reaction mechanisms was studied mo re intensively especially in regard of the influence of the reaction c onditions on the chemical, mineralogical, granulometrical and morpholo gical composition of the solids. In the presented paper investigations in the mechanisms of the reactions and the application of the Leunaka lk as a raw material in the glass industry and for the production of f illers are highlighted. It could be demonstrated that prepared Leunaka lk is suitable as calcium compound especially in decolourized glass. B y wet grinding of the lime mud with soda solution high-class fillers c an be produced. Studying the reaction of gypsum and anhydrite with hig h concentrated solutions of ammonium, sodium und potassium carbonate i t was recognized that in addition to calciumcarbonate also ammonium or potassium syngenite or gaylussite can be formed. These double salts c an be decomposed by water or react with carbonate ions. From these res ults if can be deduced that the calcium carbonate in the final product s may be formed differently and therefore also the properties of the p owders may be different. Also it must be regarded that primarily forme d vaterite can be transited into calcite.