Brick-clays from Lower-Saxony (FRG) -Technical and environmental problems

Résumé En

The raw materials used for the production of bricks can be classified genetically within the diagramm F/Al₂O₃ by means of the contents of fluorine : increased F : Detrital clay minerals as residual material from crystalline rocks normal F : Marine clays and basin clays from the Cenozoic and the Mesocoicum decreased F : New crystallised kaolinite clay of weathering zones During the firing process of brick material the emission of fluorine was influenced by the formation of crystalline phases. Due to their typical firing process hard bricks may have a lower emission rate of fluorine than normal bricks fired at the same temperatures. -Kaolinitic clays have a formation of mullite in the early stages of the firing process. This mineralisation causes a shifting of higher F-emission rates to higher temperatures. -Increased contents of CaO and of MgO (> 3 -4 wt % ) cause the formation of silicates during firing (pyroxenes, cordierite, Ca-F-Silicates ) . This effect shifts the higher F-emission rates to higher temperatures too. For the firing process of brick production the following emission rates for fluorine are dominant : Maturing temperature