# Application of Foundry Wastes in Eco-Efficient Construction Materials: A Review
## 3 Overview of the Foundry Industry
### Foundry Waste in Numbers  
Globally, more than two billion tons of municipal solid waste are generated each year. In addition to urban waste, human activities contribute with large volumes of agricultural, construction and demolition, industrial, and commercial waste, as well as waste from farms, construction sites, factories, and hospitals [63]. Countries and cities face the challenge of managing these different types of waste, which include urban solid waste and special waste, the latter being composed of industrial, agricultural, construction and demolition, hazardous, medical, and electronic waste. Certain waste streams, such as industrial waste, exceed the quantity of municipal solid waste. It is estimated that the generation of industrial waste worldwide is about 18 times greater than that of municipal solid waste [4].  
A significant portion of industrial waste comes from factories, mills, and mines. More than 50% of this waste is generated in Asia and the Pacific, especially in China. Industrial waste producers face the constant challenge of disposing of this waste and must choose between different disposal and treatment options for it [64]. Furthermore, the amount of industrial waste, at 12.73 kg per capita per day, far exceeds that of other types of special waste, including agricultural waste (3.35 kg), construction and demolition waste (1.46 kg), hazardous waste (0.32 kg), medical waste (0.25 kg), and electronic waste (0.02 kg) [4].  
Regarding industrial waste and the foundry industry, during steel production, approximately 2 to 4 tons of waste are generated for each ton of steel produced [65]. AFS reported that American foundries recycle more than 14 million tons of steel annually. Additionally, 15 to 20 million tons of scrap metal are reused every year. The association also mentions that some foundries do not generate waste; however, many states have rules and regulations that prevent the reuse of foundry materials [66]. Another report showed that, in 2022, the estimated global production of iron slag ranged between 330 million and 390 million tons, while the estimated production of steel slag ranged between 190 million and 290 million tons [67].  
Still regarding the waste from the foundry industry, the generation of foundry sand is approximately 0.60 tons for every ton of cast steel production [68; 69]. With an annual global foundry production of around 110 million metric tons [2], this results in an estimatedannual generation of about 66 million metric tons of foundry sand worldwide. In the USA, about 6 to 10 million tons of foundry sand are generated annually, with an estimated less than 15% being recycled, the rest being sent to landfalls [70]. An interesting fact is that the AFS reported in 2004 that approximately 0.5 to 0.7 million tons of foundry sand are used annually in engineering applications, with the majority applied in geotechnical uses such as landfills, land development, and road bases [71].  
In investment casting, two main residues are generated: the ceramic mold shell and the wax. According to AFS reports, investment foundries purchase 20.4 million tons of virgin wax annually [66]. Another major problem lies in the ceramic mold shell, which constitutes the majority of the waste in investment casting, representing 60% of the total generated, highlighting the importance of recycling and proper management of this process [54].