accelerated carbonation of industrial wastes
The steel manufacturing facilities are one of the major point sources of greenhouse gas emission. Another problem faced by steel industries is the waste disposal (i.e., steel slag) since the amount of steel slag produced during the steel-making process can be as high as 10 – 15 % by weight. Thus, much effort has been focused on improving the environmental sustainability of the steel manufacturing process, for example, by utilizing steel slag as an aggregate and a filler for cement. To achieve this goal, the steel slag has to be conditioned to meet the requirements of the physical and chemical properties. For example, the amounts of free CaO and MgO in steel slags need to be minimized, since free CaO leads to swelling of cement via hydration and carbonation reactions. Steel slag generally contains CaO, SiO2, MgO, Al2O3 and MnO, and is considered to be non-hazardous waste. On the other hand, Alloy steel slags, including stainless steel slag (SSS), often contain high Cr (2 – 5 %) and Ni (0.02 – 0.55 %), which classify SSS as hazardous material upon their release into the environment.
The main focus of this study is to accelerate the carbonation of SSS for the production of value-added products, while capturing CO2. The SSS was procured from an Italian steel company and both a batch reaction system and a fluidized bed reactor are used to carry out the two-step carbon capture process: (a) the extraction of Ca from SSS and (b) the capture of CO2 using a high pH Ca-rich solution. The carbonated solid products are then characterized to determine the overall capture capacity as well as the environmental safety of the proposed method. The effects of reaction conditions and chemical additives on the chemical composition, particle size and morphological structure of the solid products are investigated.
Examples of Precipitated Calcium Carbonate (PCC) synthesized under various reaction conditions