Multi-scale Analyses Of Molten Structure And Properties Of FeO-SiO₂-V₂O₃System

It is widely accepted that molten slag is an important reaction medium in the hightemperature metallurgical process, and its molten structure and properties play a vitalrole in the high efficient separation and extraction of valuable elements. Consequently,the molten structure and properties of slags win the wide attention from metallurgicalengineers and researchers. However, the molten structure of slags is relatively hard to becharacterized accurately by experiments due to their molten state and the coupledreactions between the oxide components. In contrast, the measurements of theproperties of slags are relatively easy. Still, these measurements are of some blindnessand the underlying mechanisms of the trends presented by the experimental data cannotbe directly reached. Actually, it is the deficiency of our accurate understanding on themolten structure of slags. The key of solving the above-mentioned problem isconnecting the composition, structure and properties, and bridging the scale differences.For the above considerations, this work focused on the multi-scale analyses of themolten structure and properties of the FeO-SiO₂-V₂O₃system produced from vanadiumextraction process with techniques such as DFT-based ab initio calculations, moleculardynamics simulations and X-ray diffraction etc. Starting from composition, moltenstructure of the FeO-SiO₂-V₂O₃system has been simulated and further calculations ofthe properties based on the molten structure have been carried out. Specifically, thefollowing results have been achieved.â‘ At the electronic scale, interionic interaction potentials between ions in theFeO-SiO₂-V₂O₃system were deduced from energy calculations for a two-atom modelvia the DFT-based ab initio calculations. In combination with Mulliken charge analysis,the charge of oxygen ion was determined and the charges of other ions were alsodeduced by electric neutrality. Furthermore, the interaction potentials were thusdecomposed and fitted with the BMH potential function, and a series of potentialparameters for the FeO-SiO₂-V₂O₃system were thus constructed.â‘¡At the atomistic scale, the molten structure and properties of theFeO-SiO₂-V₂O₃system of different temperatures and compositions were simulated bymolecular dynamics with the constructed potential parameters. Moreover, therelationship between the dynamic properties and the structure was established based onthe statistic mechanics, and the diffusion coefficients of ions and shear viscosity were thus calculated. The results have demonstrated the formation of clusters in molten slags.The clusters were mainly consisted by Si, V and O ions. The Fe ions were distributeduniformly around the clusters. The clusters were in connection and formed a series ofcomplex anions, instead of separately existing, and which resulted in the steadyshort-range ordered structure.â‘¢At the relatively macro scale, the phase structure of water quenched vanadiumslag samples were analyzed by X-ray diffraction （XRD） and scanning electronmicroscopy （SEM）, and the results showed good agreement with those of the moleculardynamics simulations. In addition, the calculated viscosities of the FeO-SiO₂-V₂O₃system via molecular dynamics simulations and statistic mechanics were in bothnumerical and tendency accordance with the experimental data.â‘£The interionic coordination distances and coordination numbers were relativelysmaller. It was indicated that the decomposition of the interaction potential was stillinaccurate, and which resulted in the overestimated short-range attraction, and henceneeded further optimization and improvement. Based on a further discussion on thepresent work, some possible solutions were thus proposed and explored. It wasdemonstrated that a combination of the modified two-atom model, cluster model andlattice inversion method might be an effective way to construct the potential parametersfor the molecular dynamics simulations of multi-component systems and was thusworth further investigation.