Revealing the solid solution tendency of tungsten ions in phases of Ordinary Portland cement clinker: A study based on experiments and DFT calculations

Abstract

The collaborative utilization of solid waste through cement kiln represents a highly effective approach in the current era for harnessing solid waste resources. In this paper, density functional theory simulations is used to predict the substitution tendency of tungsten (W) in Ordinary Portland cement (OPC) clinker. By employing experimental design, X-ray diffraction testing, and element distribution spectrum analysis, the doping preference of W ions in OPC clinker was comprehensively investigated. The findings demonstrate that a minor fraction of WO₃ firstly infiltrates C₄AF through the substitution of Fe atoms, whereas the majority of WO₃ infiltrates C₃S and C₂S secondly by substituting Si atoms, with negligible infiltration observed in C₃A finally. The substitution of Fe with W exhibits a lower formation energy compared to other ions, thereby indicating its preference for the formation of solid solutions in C₄AF. This preference is primarily determined by the overlapping distribution of WO and FeO bond order-bond length and their similar electron contributions in spatial distribution. However, it should be noted that the newly formed WO bond has weaker strength than the FeO bond, which may explain the limited solubility of W in C₄AF. The in-depth investigation of these fundamental issues is expected to offer an effective approach for enhancing solubility of W in OPC clinker through increasing content of C₄AF and silicate minerals, thereby providing valuable guidance for synthesizing OPC clinker using W-bearing solid wastes.

Keywords: Density functional theory; Ordinary Portland cement; Solid waste treatment; Tungsten curing.