Interrogation of ecotoxic elements distribution in slag and precipitated calcite through a machine larning-based approach aided by mass spectrometry

CO2 mineralization in slag has been widely investigated as a potential solution for offsetting steelmaking industry emissions. However, it can be associated with ecotoxic elements release (e.g., V and Cr). The presence of such elements in heterogenous slag at the micro-scale remains difficult for analysis since microstructural features can be missed during microscopy data inspection, thereby presenting a challenge in understanding how ecotoxic elements exist in slag. Here, an unsupervised machine learning-based technique is used to analyze slag's microstructural features. Energy Dispersive Spectroscopy (EDS) data are analyzed through Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) method. Results show that passive CO2 mineralization has occurred in situ in the studied samples, on the surface, and within their pores. Additionally, V and Cr regions with equivalent diameters < 42 µm can exist within slag, potentially making such elements prone to mobilization due to slag pulverization. Interrogation of the samples with Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS) confirms the distribution of the elements obtained from the clustering algorithm and further demonstrates that up to 84 and 9 ppm of V and Cr are incorporated in the precipitated calcite, respectively. This implies that ecotoxic elements may be immobilized through calcite precipitation

The mechanisms and microstructures of passive atmospheric CO2 mineralisation with slag at ambient conditions

Removal of CO2 already in the Earth's atmosphere through CO2 mineralisation with alkaline waste materials such as steel slag is one approach to mitigate the effects of anthropogenically-induced climate change. However, the microstructures produced during passive carbonation of slag are not well known. Here we use Scanning Electron Microscopy imaging and chemical mapping, X-Ray diffraction and stable isotopes (δ13C and δ18O) to show that ingassed and hydroxylated atmospheric CO2 reacts with Ca leached from slag to precipitate calcite directly on the slag surface. Precipitated calcite crystal morphologies vary, ranging from bladed and acicular crystals to layered deposits of micron-scale equant crystals. The variable morphology and extent of calcite precipitation documented is linked to a combination of internal (i.e. microstructural properties of the slag itself) and external (environmental conditions) factors. This work shows that atmospheric CO2 can be drawn down and mineralised passively by the slag at ambient conditions as part of the slag valorisation and reutilisation process

Interrogation of ecotoxic elements distribution in slag and precipitated calcite through a machine learning-based approach aided by mass spectrometry

CO2 mineralization in slag has been widely investigated as a potential solution for offsetting steelmaking industry emissions. However, it can be associated with ecotoxic elements release (e.g., V and Cr). The presence of such elements in heterogenous slag at the micro-scale remains difficult for analysis since microstructural features can be missed during microscopy data inspection, thereby presenting a challenge in understanding how ecotoxic elements exist in slag. Here, an unsupervised machine learning-based technique is used to analyze slag’s microstructural features. Energy Dispersive Spectroscopy (EDS) data were analyzed through Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) method. Results show that passive CO2 mineralization has occurred in-situ in the studied samples, on the surface and within their pores. Additionally, V and Cr regions with equivalent diameters &lt; 42 µm can exist within slag, potentially making such elements prone to mobilization due to slag pulverization. Interrogation of the samples with Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS) confirms the elements distribution obtained from the clustering algorithm and further demonstrates that up to 84 ppm and 9 ppm of V and Cr are incorporated in the precipitated calcite, respectively. This implies that ecotoxic elements may be immobilized through calcite precipitatio