Stabilization of free CaO in molten BOF slag by addition of silica at high temperature

The unstable free CaO (f-CaO) has always been the bottleneck that limits the application of basic oxygen furnace (BOF) slag as a construction material. In this work, silica was regarded as the stabilization addition to make the f-CaO in molten BOF slag stabilized at high temperature. The influences of experimental conditions on the f-CaO stabilization were studied. The results show that the main influential factors on elimination rate of f-CaO are the ratio CaO/SiO2 , reaction temperature and stabilization time. In this work setting conditions, with the ratio CaO/SiO2 less than 2.7, the reaction temperature under 1525 °C and the stabilization time over 10 min, the f-CaO content in the stabilized slag falls to the level of less than 3.00%, which can fully meet the Chinese national standard of steel slag powder used for cement and concrete. Additionally, the XRD results indicate that f-CaO is stabilized by silica in forming akermanite phase at high temperature. Moreover, the observation obtained from FESEM indicates that the undissolved lime and precipitated CaO changed into clustered CaO in the stabilized slag with its size ranging from 0.6 µm to 2.5 µm.

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