In Germany, around 30 million tonnes of Portland cement are burned every year - at the expense of the environment. After all, each tonne of cement consumes considerable amounts of energy and releases large amounts of carbon dioxide (CO2).
State of the art
Limestone, clay and sand (silicon dioxide) are mixed and grinded to produce Portland cement. This so-called raw meal is deacidified at around 800°C and then burnt to cement in a rotary kiln at 1450°C. After cooling, the resulting clinker (tricalcium silicate) is ground with additives and used as a hydraulic binder. When using mixtures with a lower lime concentration, Belit cement (dicalcium silicate) can be burnt at about 1250°C, but it is less reactive.
Scientists at the Institute of Technical Chemistry (ITC) at KIT are working on making cement production more resource-efficient. With the aid of raw materials containing calcium carbonate and silicon dioxide and by adding a mineralization additive such as sodium carbonate, the reaction temperature is decreased to such an extent that in an atmosphere rich in CO2, the raw materials react to form dicalcium silicate at temperatures as low as around 1000°C. Using aluminum-containing raw materials, sodium aluminates are formed during the calcining reaction with sodium carbonate, which dissolve in water and can be precipitated with the addition of CO2 as aluminum hydroxide and selectively separated to produce aluminum metal therefrom. The sodium hydroxide contained in the washing solution is converted to sodium carbonate and can also be separated and used again as mineralization additive in calcination. The resulting Belit cement can be added to conventional Portland cement and thus improve its CO2 balance.
The low temperature dicalcium silicate production described above requires about 30 percent less energy than limestone deacidification. It is therefore of particular interest as a substitute for calcium oxide in aerated concrete / sand-lime brick production. The new calcination process enables the production of aluminium from raw and residual materials in addition to the production of low-CO2 cementitious binders.
Options for companies
The processing was tested in the laboratory. KIT is looking for partners to further develop the technology, especially with regard to scaling for large production plants.
Your contact person for this offer
Dr. Rainer Körber,
Karlsruhe Institute of Technology (KIT)
Innovation Manager, Innovation and Relations Management (IRM)
Phone: +49 721 608-25587