Microstructural analysis of slag properties associated with calcite precipitation due to passive CO2 mineralization

Interrogation of Ecotoxic Elements Distribution in Slag and Precipitated Calcite through a Machine Learning‐Based Approach Aided by Mass Spectrometry

“…To illustrate, in sample B, it is observed that an intermediate layer is evident between the calcite cluster and the matrix phase. We previously documented the existence of similar layers at the interface between slag minerals and the precipitated calcite in pore space within other slag samples, [36] where we attributed the observed layers to the dissolution of calcium ions from complex minerals that dissolve nonstoichiometrically as reported elsewhere. [42] Our previous observations demonstrated that this layer is homogenous and predominantly composed of Si and O.…”

“…Previous work demonstrated that slag can be used in passive CO 2 mineralization, although the observed CO 2 uptake is usually low, that is, in the order of 60 kgCO 2 /1000 kg slag. [36,44] Consequently, it has been suggested that slag size reduction through pulverization can be used to increase the CO 2 uptake rate. For example, the size reduction of slag average diameter from 532.1 to 43.9 μm increased the CO 2 uptake by around two orders of magnitude under the same experimental conditions, and they attributed this rise to increasing the dissolution rate of slag minerals.…”

“…Details about the location of this site and its history were summarized in the previous study. In light of the previous observations of microstructural features of slag and previously acquired backscattered electron images of slag, [31,36,32] three samples (A, B, and C) were shortlisted for the present analysis. These samples were selected so that they reflect the variation in slag sample microstructure (e.g., presence of pores space, presence of materials with different atomic numbers, presence of pore filling materials and precipitates) and so they demonstrate different calcite precipitation patterns (i.e., in pore space and on the external surface of the slag).…”

“…Raman spectroscopy and EDS clustering analysis of samples A and C show that they contain åkermanite-gehlenite minerals, which are commonly observed in BF slag, and their presence has been documented in this site and several sites worldwide. [14,[33][34][35][36] For sample B, however, Raman spectra taken from different spots within the matrix could not be indexed. We speculate that these observed Raman spectra are a consequence of alteration that different mineral phases are subjected to during the steelmaking process, or during the chemical alteration that slag may be subjected to during hydration and subsequent minerals dissolution.…”

“…Unlike our previous observations, however, the thickness of precipitated calcite reaches 300 μm versus a maximum thickness of 50 μm observed in our previous study. [36] We attribute this to the fact that the currently investigated samples were collected from a pond near the slag deposit site. Consequently, the water enhanced the calcite precipitation, in contrast to our previous study in which calcite precipitation took place within the pore space of the samples.…”