Carbonation-granulation of alkali activated BOF slag for the production of recycled aggregates and CO2 storage

This work was aimed at investigating the performance of a combined carbonation and granulation treatment applied to Basic Oxygen Furnace (BOF) steel slag with the aim of producing secondary aggregates and of storing CO2 in a solid and stable form. In order to improve the mechanical properties of the aggregates, an alkaline solution of sodium silicate and sodium hydroxide was employed as binder instead of water both during the granulation and combined granulation/carbonation tests. The results showed that the granules produced using the alkali activator with or without CO2 addition, presented a mean size ranging from 1 to 5 mm and adequate mechanical properties for use in civil engineering applications. The maximum CO2 uptake attained was of 40 gCO2/kg steel slag for the alkali activated and carbonated granules after 60 min of treatment. As for the leaching behaviour of the produced granules, an increase in the release of Cr and V was found for the product of the granulation/carbonation treatment with alkali activation; nonetheless, the crushed granules attained after a reaction time of 30 min showed to still comply (apart from pH) with the Italian requirements for reuse for land reclamation.