## 3 Factsage in the Environmental Sector
### Application in the Field of Solid Waste
In the study of thermal treatment of solid waste, Factsage can effectively analyze the physical and chemical changes of industrial solid waste at high temperatures using its Equilib module and Phase Diagram module, and provide insights on the optimal thermal treatment conditions and raw material ratios based on the effects of each component on the physical phase changes and physicochemical properties [132; 133; 134]. Factsage can be used for the study of waste incineration fly ash melting treatment. For example, [PERSON] et al. [87] calculated the product and liquid phase line temperatures of waste incineration fly ash and fly ash synergistic melting treatment by using the Phase Diagram and Equilib module, and verified the results with each other and with the actual melt results, which determined the credibility of the simulation results of the software. [PERSON] et al. [126] mainly calculated the physical phase change process and viscosity change of waste incineration fly ash in the melting process by using the Equilib and Viscosity module, determined the feasibility of a metallurgical shaft furnace reactor to treat waste incineration fly ash, and provided theoretical data and optimal reaction conditions for subsequent experiments. On the other hand, Factsage has the capability to simulate and calculate the incineration process of sludge, providing a theoretical basis for optimizing the sludge incineration process [135; 136; 137]. For instance, [PERSON] et al. [127] mixed sludge with coal for combustion and used the Equilib module to thermodynamically calculate and simulate the evolution of iron- and sulfur-containing compounds in the mixed combustion process, providing a theoretical basis for sludge combustion treatment and addressing the issue of pollutant emission during the process. To validate the correctness of the thermodynamic calculations, the samples were incinated and the ash was characterized; the simulation results of the software were found to be reliable based on the characterization results. Since sludge contains certain heavy metal elements, it may cause secondary pollution during the combustion process. [PERSON] et al. [128] addressed this issue by using the simulation calculations of the changes in the chemical morphology of heavy metals during incineration with the Factsage. They eventually determined the effect of the morphological characteristics of fine particulate matter with temperature, sludge particle size, and content of additive CaO on the fugitive morphology of heavy metals. Additionally, Factsage can be used to simulate the process of new materials such as microcrystalline glass and ceramics using solid waste at high temperatures, promoting the harmlessness and resourcefulness of solid waste treatment [138; 139]. In the process of preparing new environmentally friendly materials, the elemental composition of the envisioned raw materials can be entered into Factsage. Subsequently, the temperature, air pressure, and other process conditions can be entered, enabling the phase composition and properties of the final new materials to be calculated using the Equilib module through the Gibbs Least-Free-Energy Algorithm and Functions. By continually modifyingthe proportion of the constituent raw materials and the reaction conditions, the optimal conditions for the synthesis of the new materials can be identified. Subsequently, the optimal conditions are employed to conduct the actual preparation experiments of the new materials, with the results being validated against the simulation outcomes to elucidate the generation mechanism of the new materials' phases. The utilization of Factsage has the potential to streamline the investigation of novel materials, whilst simultaneously furnishing a theoretical foundation for the advancement of innovative methodologies. When studying metal resource recovery technologies for solid waste, Factsage can be utilized to simulate and optimize the recovery process, providing a theoretical foundation for practical operations [140; 141; 142].