Fabrication and Quantification of Chromium Species by Chemical Simulations and Spectroscopic Analysis

Chromium (Cr) exists in multiple oxidation states, with Cr(III) and Cr(VI) being the most environmentally and industrially relevant due to their distinct toxicity profiles and chemical behaviour. This study presents a comprehensive method that combines chemical simulation modelling, emission spectroscopy for quantification, and the controlled laboratory production of Cr species. Key findings include that acid digestion effectively extracted the Cr(III) and total Cr species, while thermodynamic modelling forecasted their stability and speciation under various environmental conditions. Thematic analysis indicates that the current quantification of Cr species is still in early development and remains centralized. Mineralogical and surface investigations showed that samples 1 and 2 have a BET surface area below 1 m2/g, whereas samples 3 and 4 exceed this. All samples are crystalline, with approximately 54.3 weight percent Cr2O3, 7.3 weight percent SiO2, 17.75 weight percent of MgO, and 8.3 weight percent Al2O3, suggesting Al and Fe2+ replacement of Cr in the spinel structure. Computational fluid dynamics (CFD) modelling revealed that longer residence times are necessary for higher Cr metallization under H2-CH4-reducing conditions, and accurately predicted carbon deposition on pellets. These results demonstrate that CFD can optimize the H2:CH4 ratio to minimize carbon deposition and enhance gas transport to reaction sites.