Valorization of steel slag by a combined carbonation and granulation treatment

This work reports the results of a combined accelerated carbonation and wet granulation treatment applied to Basic Oxygen Furnace (BOF) steel slag after crushing for metal recovery with the aim of producing secondary aggregates for civil engineering applications and of storing CO2 in a solid and thermodynamically stable form. The tests were carried out in a disc granulator equipped with a lid and CO2 feeding system. In each test, humidified slag (liquid/solid ratio of 0.12 l/kg) was treated for reaction times varying between 30 and 120 minutes under either atmospheric air or 100% CO2. Results indicated that, under both conditions, the particle size of the treatment product increased progressively with the reaction time; specifically, the d50 values obtained for the products of the combined granulation and carbonation treatment increased from 0.4 mm to 4 mm after 30 min and to 10 mm after 120 min. Significant CO2 uptake values (between 120 and 144 g CO2/kg) were measured even after short reaction times for granules with diameters below 10 mm and for coarser particle size fractions after reaction times of 60 minutes. The density, mineralogical composition, leaching behavior and mechanical resistance of both granulated and granulated-carbonated granules were also investigated