Granulation–Carbonation Treatment of Alkali Activated Steel Slag for Secondary Aggregates Production

Abstract

In view of the EU's circular economy strategy, there is a need to develop treatments that may allow to improve the management of industrial residues such as steel manufacturing slag, for example by producing secondary products that may be used for different applications. This work evaluates 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 CO 2 in a solid and stable form. In order to improve the mechanical properties of the product, a solution of sodium silicate and sodium hydroxide was tested as binder instead of water in both the granulation and combined granulation-carbonation tests. The results showed that the granules produced using the alkali activator with or without CO 2 addition, presented a mean size ranging from 1 to 5 mm and adequate mechanical properties for use in civil engineering applications. The maximum CO 2 uptake attained was of 4% wt. for the alkali activated and carbonated granules after 60 min of treatment and 7 days curing. 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. Instead, granulation with alkali activation or granulation with carbonation showed to decrease the release of Ba and Cr with regard to the untreated residues.

Carbonate-bonded construction materials from alkaline residues

“…Besides the potential increase of the leaching of Cr and other oxyanion-forming elements, the main barrier to produce carbonate-bonded aggregates according to this process was the mechanical properties. Latest developments show that for BOF steel slag this issue can be addressed by using alkaline activators although in this case the leaching of Cr and V did not comply to leaching limits for unbound use, nor did the product pH [51].…”

Exploring the Potential for Utilization of Medium and Highly Sulfidic Mine Tailings in Construction Materials: A Review

“…Innovative techniques are therefore required to allow for the use of such materials as aggregates in construction. The techniques of granulation or combined granulation/carbonation have been employed to produce secondary aggregates from fly ash [141], basic oxygen furnace (BOF) steel slag [142,143], MSWI ash [144,145], and mine tailings [146]. Improvements in particle size distribution are obtained by the production of granules with adequate mechanical properties for civil engineering applications, as well as reduced leaching of contaminants and CO 2 uptake.…”

CO2 Utilization and Long-Term Storage in Useful Mineral Products by Carbonation of Alkaline Feedstocks

“…Carbo-granulation applied to ground BOF slag allowed to achieve a significant increase in particle size and a CO 2 uptake of around 10% by weight (Morone et al, 2014). However, alkaline activation, consisting in the use of a sodium silicate/sodium hydroxide solution instead of water as binder, proved necessary to attain granules with a mechanical strength close to the one typically exhibited by gravel (Morone et al, 2017). Carbon8 Systems have achieved commercial operation of plants that make use of alkaline waste materials, APC residues in particular, concentrated CO 2 streams, and other FIGURE 1 | Scheme of current CO 2 utilization pathways for producing carbonated materials to use in construction or other applications.…”