Solidification behaviour of soluble Mn in blended cement with metallurgical slag

The utilization of metallurgical slag for the partial substitution of clinker to produce blended cement is an effective approach for the harmless and resourceful disposal of industrial solid waste. Nevertheless, the influence of metallurgical slag on the solidification behavior between clinker minerals and heavy metals remains unclear in blended cement. In this study, the blended cement is composed of cement, synthetic amorphous phase (eliminating the influence of physical-chemical characteristics of different metallurgical slags), and different levels soluble Mn. The study applied various characterization methods focusing on the solidification behaviour of Mn in the hydration process of blended cement. The results reveal that Mn exhibits a dual effect on the reaction of C 3 S, with the appearance time of the main peak in the hydration heat curve extending from 10 h to 17 h (when Mn dosage reaches 0.9 wt%). However, with the increase of Mn, the main peak appeared early at 5.6 h. The primary inhibitory factor for the C 3 S hydration reaction is Mn-bearing hydrate phases on the surfaces of cement particles. However, when the soluble Mn content exceeds a certain threshold (2.7 wt% in this study), the clinker reaction is enhanced due to the formation of additional nucleation sites by Mn-hydrate precipitates. Mn is predominantly solidified within the gel-like hydration products and ettringite through lattice confinement and physical encapsulation. The introduction of Mn promotes the formation of ettringite-like products. This reaction consumes gypsum and thus accelerates the secondary hydration of C 3 A. The improved hydration kinetics model is employed to reveal the hydration mechanism of blended cement containing Mn. The hydration process of blended cement follows a diffusion-controlled behaviour, which is influenced by the Mn-precipitation layer. These findings provide comprehensive insights into reaction kinetics and the solidification of heavy metals, contributing to the sustainable application of metallurgical slag in the environment.