Slurry-phase carbonation of different types of steel slag: CO2 uptake and effects on mineralogy

This paper reports the main results in terms of CO2 uptake and conversion yield attained by three different types of residues from steel manufacturing subjected to accelerated carbonation. Electric arc furnace (EAF) slag and two basic oxygen furnace (BOF) slag samples were investigated. Both a wet (L/S = 0.3 l/kg) and a slurry-phase route (L/S = 10 l/kg) were applied for batch accelerated carbonation tests at controlled temperature and CO2 pressure. The CO2 uptake achieved upon the treatment varied significantly depending on the type of investigated slag and on the process route adopted; maximum values of 280, 325 and 404 g CO2/kg slag were achieved for EAF, BOF1 and BOF2 slag, respectively, under slurry-phase conditions (T = 100 °C, pCO2 = 10 bar). The results indicated that the effects of accelerated carbonation, assessed in terms of CO2 uptake capacity and mineral conversion into carbonates, are strongly dependent, above all, on the mineralogy of the original material and the operating conditions adopted, which thus need specific case-by-case optimization.