In the casting process, molding sands are recycled and reused multiple times, but after going through many production cycles, they become less uniform and lose their cleanliness. The sand grains begin to break down because of heat and mechanical abrasion, and therefore new sand must be continually added to the system. When waste foundry sands (WFS) are no longer suitable for the manufacturing process, they are removed from the system and discarded at foundry landfills or offsite municipal landfills [2].  
It is estimated that approximately 100 million tons of sand are used in annual production, and 6-10 million tons are discarded annually and available to be recycled into other products and industries [3]. Further, about one ton of foundry sand is used for each ton of iron or steel casting produced [4]. Meanwhile, the foundry industry in Italy produces 1.5 million tons of raw casting and generates about one million tons of waste, most of which (around 80%) is sand. The automotive industries are the major generators of foundry sand (about 95% of the estimated WFS) [2].  
As millions of tons of waste foundry sands are generated each year, their disposal has become an environmental challenge [5]. Foundry sand can be classified as a hazardous or non-hazardous material, depending on its source. Silica-based spent foundry sands, specifically from iron, steel, and aluminum foundries, are considered non-hazardous, while spent foundry sands from leaded brass and bronze foundries are often regulated as hazardous waste because of the presence of highly toxic organic pollutants that can contaminate the atmosphere or condense in the sand. These pollutants include phenols and inorganic elements such as lead, chromium, cadmium, iron, and zinc [6]. Even though the analysis of the leachate obtained from waste foundry sands has found that the concentration of most hazardous substances is below the acceptable limits, hazardous polyaromatic hydrocarbons have been found in all types of waste foundry sands [6]. Waste foundry sands should be dumped into controlled landfills; however, because of the growing waste foundry sands production and the need for landfill monitoring, the landfilling cost has been continuously increasing in the past years, reaching 5135-657 million in the U.S.A. [7], making unviable to continue with this practice.  
Consequently, recycling waste foundry sands into several applications has become an attractive opportunity to decrease the economic and environmental impact of their disposal [8]. Although natural materials are often preferred in terms of quality, their sources are depleting gradually over the years, making the use of waste materials viable [7; 9; 10].  
Silica-based WFSs are classified as non-hazardous residues and can be used in other industries as secondary raw materials. For example, they have been used in the sustainable building sector, specifically in cold consolidated materials such as cementitious conglomerates, asphalts, concrete, and cement [11]. Ceramic materials regulations allow the use of secondary residual raw materials to replace sands normally used as inert material in the production of ceramic tiles and bricks, therefore contributing to the reduction of the environmental impact of their activities [12]. Other types of products suitable for exploiting foundry sands are geopolymers, materials obtained through the cold alkaline activation of suitable precursors. In geopolymers, foundry sands are potentially interesting as precursors and/or as fillers or aggregates to obtain geopolymer mortars [12; 13]. In this work, we investigated the potential application of WFS, obtained from different Italian metal casting industries, in geopolymers and ceramic tiles formulations.