CO2 mineral sequestration with the use of ground granulated blast furnace slag

The mineral sequestration using waste products is a method of reducing CO2 emissions that is particularly interesting for major emitters and producers of mineral wastes, such as iron and steel industries. The CO2 emissions from iron and steel production amounted to 6,181.07 kt in 2014 (PNIR 2016). The aforementioned industry participates in the EU emission trading system (EU ETS). However, blast furnace processes produce mineral waste - slag with a high content of CaO which can be used to reduce CO2 emissions. Metallurgical slag can be used to carry out direct (a one-step process) or indirect (two-stage process) process of mineral sequestration of carbon dioxide. The paper presents the degree of carbonation of the examined samples of granulated blast furnace slags defined by the six-digit code (10 02 01) for the waste and the respective two-digit (10 02) chapter heading, according to the Regulation of the Minister of the Environment of 9 December 2014 on the waste catalogue. The carbonation process used the direct gas-solid method. The slags were wetted on the surface and treated with CO2 for 28 days; the obtained results were compared with the analysis of fresh waste products. The analyzed slags are characterized by a high content of calcium (nearly 24%), while their theoretical binding capacity of CO2 is up to 34.1%. The X-ray diffraction (XRD) analysis of the phase composition of slags has revealed the presence of amorphous glass phase, which was confirmed with the thermogravimetric (DTA/TG) analysis. The process of mineral sequestration of CO2 has resulted in a significant amount (9.32%) of calcium carbonate - calcite, while the calculated degree of carbonation of the examined blast furnace slag is up to 39%. The high content of calcium, and a significant content of CaCO3-calcite, has confirmed the suitability of the discussed waste products to reduce carbon dioxide emissions.