# Application of Foundry Wastes in Eco-Efficient Construction Materials: A Review
## 3 Overview of the Foundry Industry
### Foundry Industry Waste Management
The used clay is extracted as fine material, and the sand is restored to its specifications with the addition of new sand, clay, resin, and other additives [26]. There are still few data on the use of foundry sand outside the internal reclamation process in foundries. However, WFS has found applications as a substitute for fine aggregates in construction projects and as feed material in furnaces to produce Portland cement. Most of the foundry sand used in green sand operations is generally disposed of in landfills [46]. Another type of waste generated by the foundry industry is slag. The interest in steel slag has ancient origins, with Basic Bessemer or Thomas process steel slag being used as a phosphatic fertilizer since the 1880s. Curiously, around 350 B.C., [PERSON] mentioned: \"When iron is purified by fire, a stone known as iron slag is formed\". It is extremely effective in drying wounds and offers other benefits. This historical context underscores the long-standing recognition of the advantages of iron slag [47]. Steel slag is a residual material derived both from the transformation of iron into steel in a basic oxygen furnace (BOF), and from the melting of scrap to produce steel in an electric arc furnace (EAF). Granulated blast furnace slag, characterized by its vitreous structure and cementitious properties, is widely used around the world as a substitute for cement. Although research indicates the cementitious nature of blast furnace steel slag, similar to cement clinker, it is mainly used as an aggregate in asphalt concrete in many countries [48]. Some authors limit the definition of metallurgical slags to those generated in the production of iron and steel, because the foundry industry uses these materials in the process of casting liquid metal. Electric arc and electric induction furnaces are frequently used to melt steel, while the cupola furnace is preferred for melting iron. During the melting process, metal scrap and fluxes, such as limestone or dolomite, are introduced into the furnace. The application of heat, whether by electricity (arc furnace or induction  
Figure 4: Sand casting process. furnace) or by combustion (blast furnace or cupola furnace), results in the melting of scrap into a liquid phase. Gravimetric separation is then employed to extract the metal, leaving the residual slag. Furthermore, during the smelting process, furnace slag is generated, which is a non-metallic byproduct [49]. The global annual production of various types of slag highlights significant differences in their generation rates. Granulated blast furnace slag accounts for the largest share, representing 49% of the total annual production, followed by electric arc furnace slag at 33%. Steel furnace slag contributes 12%, while cupola furnace slag represents the smallest proportion, at 6% [50]. The properties of the generated steel slag can vary based on factors such as the manufacturer and the types of steel produced. Thus, before recycling steel slag into more sustainable products, it is important to carefully examine and understand its characteristics. This includes the process of steel slag formation, its chemical constituents, mineralogical characteristics, and the potential associated risks [51]. The electric arc furnace not only produces slag but also 15 to 25 dust kg/steel ton. The use of this type of oven generates fumes that are removed through an opening in the ceiling. The materials are subjected to post-combustion treatment, followed by cooling and cleaning processes, to extract and capture dust particles. The dust, collected in a specific container, presents harmful components like lead, zinc, and cadmium, and it must be disposed of in designated landfills [52]. However, the costs associated with transportation and maintenance of disposal sites have increased in recent years, and recycling operations involving this dust in certain foundries present challenges due to the need for substantial investments and rigorous control processes [53].