Effect and Mechanism of Microbial Treatment on Enhancing the Activity of RO Phase in Steel Slag

Abstract Due to the low reactivity and poor volume stability of steel slag (SS), its application in construction materials is limited. In particular, the divalent metal oxide solid solution (RO phase), due to its poor grindability, presents significant challenges for the effective activation of SS. In this study, three types of microorganisms were selected to activate SS and RO phases with different compositions. The activation mechanisms were investigated through tests on activity index, particle size distribution, and microstructure. Results showed that, under the synergistic effects of bioacid dissolution and microbial decomposition, the particles of RO/SS became finer and their reactivity improved to varying extents. Acidithiobacillus ferrooxidans ( A. ferrooxidans ), capable of utilizing Fe 2 + as a nutrient source, exhibited the best activation effect on FeO-rich RO phases, increasing the activity index from 58% to 91%. Bacillus mucilaginosus ( B. mucilaginosus ), known for its high alkali resistance, was more effective for MgO-rich RO phases, enhancing the activity index from 74% to 98%. Further, the volume stability of SS was also improved after microbial treatment, with the expansion rate reduced by 61% in samples treated with Aspergillus niger ( A. niger ).