Incorporation of antimony-bearing mining wastes into clinker Portland raw feed: The difficulty of Sb analysis in...

Within the global trend to valorise various mineral wastes as substituents in Portland cement clinker raw feed, mining wastes are promising candidates. However, they might still contain high levels of metallic elements. Their fate in the kiln is not always understood as well as their incorporation within the various clinker's phases. This is especially the case for antimony. Its in situ microanalysis by the means of energy-dispersive spectroscopy is tricky since several of its L lines (L_α1 = 3604,72 eV, L_α2 = 3595,32 eV) overlap with calcium lines (K_α1 = 3691,68 eV, K_α2 = 3688,09 eV). Hence, at low concentrations, it is not possible to visualise its characteristics peaks. Increasing the counting rate by increasing the acceleration current results in the generation of spurious sum peaks, rendering the analysis not viable. Wavelength dispersive spectroscopy (i.e. electron microprobe) allows a better spectral resolution and quantification of Sb in the clinker phases. In a Portland cement clinker doped with 1% of Sb-bearing mining waste, the Sb₂O₃ content in belite and alite is in the 0.2-0.4 wt.% range as well as for C₃A; in C₄AF the content is higher, from 1.4 wt.% to 2 wt.%. However, there are microstructural evidence that Sb forms blebs from less than 1 μm in diameter up to 10 μm, included in calcium silicates. Hence, its incorporation in the lattice of calcium silicates is dubious. However, for ferrites and aluminates there is no microstructural evidence for remaining Sb-bearing phases, suggesting a direct incorporation in crystal lattices.