Reduction of CO2 Emissions in Ceramic Production from Clay Raw Materials Containing Carbonates

The production of building ceramics is an energy-intensive part of the industry, causing high CO2 emission per production volume. In addition to the combustion of fossil fuels, CO2 is emitted as a byproduct of calcium carbonate decomposition, a compound present in clay raw materials. In this paper, a method for reducing emissions by lowering the firing temperature of ceramics, thereby preventing the complete decarbonation of carbonate minerals, is presented. Thermal research has shown that lowering the firing temperature to 750 °C resulted in a 55% calcium carbonate decomposition and a reduction in CO2 emissions by over 30 kg for every ton of clay used. At this temperature, sintering shrinkage mechanisms were not observed, which resulted in a reduction in the strength of the materials by almost 25% compared to samples fired at 900 °C. An attempt was made to compensate for the negative effects of lowering the firing temperature by adding ground glass cullet, which brought only partially positive results: an increase in flexural strength, but no change in compressive strength. Microscopic observations and phase composition studies indicate that lowering the firing temperature causes changes in the proportions of calcium compounds: increased amounts of calcite, and decreased amounts of silicates and calcium aluminosilicates.