# Application of Foundry Wastes in Eco-Efficient Construction Materials: A Review
## 3 Overview of the Foundry Industry
### Foundry Industry Waste Management
In the investment casting industry, a large amount of waste from used ceramic molds is generated. Research is being conducted to explore ways to recycle the ceramic molds used in casting. The focus is on reducing, recycling, and managing this waste effectively. An interesting possibility is to repurpose these ceramic molds used in industries such as ceramics or construction, offering a sustainable solution [54; 55]. Another waste is the wax extracted from the ceramic mold, which is composed of mixtures of waxes, polymers, and resins. In some cases, fillers such as cross-linked polystyrene are incorporated to improve the thermomechanical properties of wax components [56]. The melted wax is reused to make more patterns; however, the wax extracted from the initial ceramic mold is generally lost in this process [31]. Investment casting has a prolonged production cycle with significant energy consumption, especially in tasks such as drying and firing ceramic molds. Moreover, the molds and casting models are made of expensive materials. A challenge in investment casting is the lack of recycling of used ceramic molds. Until recently, most of this material was discarded or, at most, used as refractory filler in ceramic molds [57]. Although there is much research on sand casting and die casting, there is a shortage of publications addressing the aspects of investment casting [56]. In the literature, it is possible to find research that focuses on the use of foundry waste in the foundry process itself. The following are some of these studies. [PERSON] et al. [58] investigated how waste shell sand and various raw materials could be used to make slurry and coatings for ceramic molds. The research demonstrated the potential of geopolymer technology in investment casting, presenting an eco-friendlier method for creating ceramic molds. This advancement contributes to the reduction of waste produced and decreases the environmental impact in the foundry industry. A study on the separation of valuable material from ceramic mold waste, particularly zircon sand, was conducted by [PERSON] et al. [59]. They examined the microstructure and phase composition of the mold residues to identify conditions for the separation of zircon sand. This successful separation process can bring benefits to the investment casting industry, reducing recycling costs and preventing the disposal of valuable resources. In another study, [PERSON] et al. [60] reused waste from precision casting processes, specifically the ceramic mold, to produce ceramic filters. By impregnating polyurethane sponges with a suspension, it was possible to produce high-quality filters with improved mechanical strength. The filters demonstrated good filtration efficiency for liquid cast iron, showing their potential for industrial uses. [PERSON] et al. [61] presented a study that explored the potential of recycling ceramic mold waste within the production process itself. However, it was necessary to isolate valuable materials, including chamotte and zirconium. Additionally, it was concluded that the crystalline silica fraction should be removed, as it can compromise the performance of the recycled ceramic shell. This fraction may cause expansive reactions, leading to a weakness in the ceramic shell. The introduction of waste management practices in the foundry sector can offer a series of advantages, both for the environment and for the industry itself. The use of residual materials presents an opportunity to reduce dependence on natural raw material reserves, decrease mining activities and the associated environmental hazards, improve waste management efficiency, and reduce the occupation of landfill areas. The optimized reuse of waste through transformative technologies facilitates the production of value-added products, contributing to sustainability in manufacturing [62].