The presence of residual free lime (CaO) in Basic Oxygen Furnace (BOF) slag is one of the major obstacles to its sustainable re-use as an aggregate in construction practices. Because of the short term hydration and the long term carbonation of free lime, BOF slag aggregates present a potential for problematic volume expansion (swelling) resulting in rapid deterioration of the material. Hot-stage carbonation can be a promising and novel stabilization treatment route. This approach takes advantage of the heat source of the slag during slag cooling to allow rapid, low-cost and targeted mineral carbonation at elevated temperatures, given, respective, the favorable kinetics, the freely available thermal energy, and the unique susceptibility of CaO to carbonation at elevated temperatures. Capture of CO2 occurring during carbonation is also favorable for emissions reduction. Lab-scale experiments have been designed to simulate the hot-to-cold stage path of the molten slag and to investigate the kinetics of the slag carbonation reaction along this path. The influence of different process parameters (the residence time, the solid-gas contact method, and the particle size) on the carbonation conversion is highlighted in order to identify the key parameters for developing the envisioned ‘’carbonation during granulation’’ route. BOF slag batches were solidified under production conditions (in the slag yard), then crushed and sieved to four particle size fractions for carbonation studies: &lt; 0.1 mm, 0.1-0.2 mm, 0.2-0.5 mm and 0.5-0.7 mm. The chemical composition of BOF slag was determined by X-ray Fluorescence (XRF, Panalytical PW2400), and the mineral composition was determined by X-ray Diffraction (XRD, Brucker D2 Phaser) with Rietveld refinement technique (Topas Academic v4.1). Carbonation experiments were conducted at atmospheric pressure at various temperature profiles using two different reactors: a fluidized bed reactor (FBR) and a tubular furnace (TFr). The CO2 uptake was quantified by thermogravimetric analysis (TGA, TA Instrument Q600). The results obtained highlight that the carbonation conversion occurs predominantly, and is the fastest, during the 10 first minutes of cooling from 700 oC. The reaction kinetics are also directly proportional to the gas/solid contact, and inversely proportional to the particle size. These promising results show that the hot stage carbonation presents a double benefit: to sequester CO2 and to stabilize BOF slag.

Kinetics of hot-stage carbonation of basic oxygen furnace slag for reduction of free lime content

254th National Meeting (2017)

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