## 2 Function of Factsage Software
### Viscosity Module  
Dynamic Viscosity, as a physical property, is closely tied to the structural characteristics of slag. It plays a pivotal role in influencing parameters like desulphurization rate and heat transfer rate within the slag. Consequently, understanding viscosity holds considerable importance, especially in the investigation of heat treatment processes applied to industrial solid waste under high-temperature conditions. By accurately predicting viscosity, the process parameters can be efficiently optimized. Table 2 shows examples of the application of the Viscosity module by researchers in various fields. The Viscosity module calculates the viscosity of a solution or glass under single-phase liquid conditions. It relates viscosity directly to the structure of the solution, which is derived from a thermodynamic description of the solution using a Modified Quasichemical Model (2018). In addition, new models are being developed, as exemplified by [PERSON] et al. (2018) who have introduced a viscosity model for oxide melts containing zinc oxide. To guarantee the precision of the model, the authentic viscosity of the melt comprising ZnO with SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), CaO, MgO, Na\({}_{2}\)O, K\({}_{2}\)O, and PbO was meticulously gathered. The true viscosities of the melts were compared with the viscosity data predicted by the model and were found to deviate by no more than the dispersion of the experimental points between the different authors used to calibrate all binary and ternary subsystems of the ZnO-SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\)-CaO-MgO-Na\({}_{2}\)O-K\({}_{2}\)O-PbO model. This model has undergone both experimental and computational validation and has been integrated into the viscosity calculation module within the Factsage. This integration ensures accurate viscosity prediction for multicomponent melts, providing a theoretical basis for processes such as pyrometallurgical zinc metal recovery and glass production. Despite its simplicity, this module is widely used in several industries (2018); (2018); (2018); (2018). Viscosity is one of the important physicochemical properties of melts, so it has been used in the study of high-temperature melt treatment of solid waste processes in the environmental field. For example, [PERSON] et al. (2018) used the Equilib and Viscosity modules to simulate the effect of the preparation process of ceramic aggregates on ceramic aggregates, thus enabling the exploration of economical, efficient, and feasible sintering processes with limited high-temperature experiments, which not only saves a great deal of time but also \begin{table}
\begin{tabular}{c c c} \hline \hline
**Application Area** & **Case Descriptions** & **Reference** \\ \hline Modelling the viscosity of zinc & A viscosity model for oxide melts containing zinc oxide was & \\  & constructed, validated through experimental and computational & \\  & means, and subsequently integrated into the Factsage Viscosity & [(2018)] \\  & module to guarantee the precision of the predicted viscosity values & \\  & generated by Factsage. & \\ \hline Preparation of ceramic aggregates & Simulation of viscosity changes during the sintering of ceramic raw & \\  & materials using Viscosity to determine the optimum sintering & [(2018)] \\  & process for the production of ceramic aggregates. & \\ \hline Predicting desulphurization slag & The viscosity of desulphurization slag was predicted using various & \\  & models and compared, and the results showed that Factsage had & [(2018)] \\  & the best prediction results, with an absolute error value of less than & \\  & 0.1 Pa-s. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Application study of the Viscosity module of Factsage software. reduces energy and material consumption. Meanwhile, the Viscosity module predicts the viscosity very accurately, and its absolute error is reduced from 0.25 Pa-s to 0.1 Pa-s compared with the Watt-Fereday model when predicting the viscosity of the desulphurized iron slag with a real viscosity of 0.8 Pa-s [56].