The influence of glassy wastes on the sintering process of Portland cement clinker

The main challenge for the European cement industry in the last decade is so-called decarbonisation, i.e. reducing CO2 emissions throughout the entire production cycle. In the case of the cement industry, this task is difficult because most CO2 emissions come from the thermal dissociation of calcite present in raw materials for the production of Portland clinker. The main way to reduce CO2 emissions from this source is to use calcium oxide sources in non-carbonate form. In practice, however, the availability of such raw materials in Europe is very limited, and their import from other continents is not only unprofitable, but also environmentally unfriendly due to emissions generated during transport. However, there are examples of the use of waste raw materials containing calcium oxide in the Portland clinker production. These include, among others, granulated blast furnace slag, converter slag, carbide lime, lime ash, as well as glass cullet which is the subject of analyses. The aim of the research is to analyse the burnability of clinkers with the addition of various glass wastes. The glass wastes selected were those that could not be reused in glass production due to contamination and fine-grained form. The use of glass cullet was quantitatively limited due to the high Na2O content [13 % –15 %]. Glass waste introduced into the raw material batch is mainly a source of SiO2 [67 % –- 69 %] and to a lesser extent CaO [9.0 % - 12.4 %]. The introduction of even small amounts of cullet increases the demand for high-lime raw material and also raw materials that are sources of Al2O3 and Fe2O3. Although glass waste introduces CaO in a non-carbonate form, the above changes in the raw material feed combined with the presence of carbonates in raw materials other than calcite [dolomite, siderite] mean that the addition of glass cullet does not necessarily reduce CO2 emissions from raw materials. The positive effect of the addition of glass waste on the burnability of raw material batches is noticeable at temperatures of 1200 °C – 1250 °C. It is probably related to the high Na2O content in the glassy waste and its amorphous form.