Filter cakes are used as plastic additives in the brick and tile industry. They have characteristic material properties and depending on their mineralogical composition, they improve thermal insulation or other product features.
The grain size distribution of filter cakes is displayed in the Winkler triangle. It shows that filter cakes can be ideally used for traditional brick products. They have a homogeneous composition and only contain grain size fractions smaller than 0.4 mm. Filter cakes are free of geogenic coarse components such as wood, pyrite, calcite or quartz aggregates.
Filter cakes are elutriated and drained mineral slurries from the production of industrial rocks and minerals with geogenic clay mineral content. In brickworks the use of filter cakes is very energy efficient because they do not have to be crushed. They simply need to be mixed homogenously with the other clay mass components. The use of filter cakes reduces the abrasive wear of the processing unit.
Most filter cakes from the aggregates and crushed stone industry are excess material from mineral washing. With a distinct focus in the Paleozoic especially the Devonian, filter cakes can be obtained from rocks of a very long stratigraphic record of the Early Devonian to the Neogene.
In the German aggregate industry, there are about 20 locations/plants with installed chamber/membrane filter presses. Further press locations are planned nationwide. Each plant produces 15 000 to 200 000 t of filter cake a year. An average annual tonnage is about 30 000 t. The clay mineralogical and ceramic characteristics of the filter cake are strongly influenced by the type of source rock.