groundwater with pH values above 12. The calcium silicates (CaSiO4) in slags react with water to produce calcium hydroxide ions that leads to a higher concentration of hydroxide (OH-) in ground water. This alkalinity promotes the mineralization of dissolved (from the atmosphere) to produce calcite (CaCO3), which can accumulate to as thick as 20 cm. This can also lead to the dissolution of other metals in slag, such as iron (Fe), manganese (Mn), nickel (Ni), and molybdenum (Mo), which become insoluble in water and mobile as particulate matter. The most effective method to detoxify alkaline ground water discharge is air sparging. Fine slags and slag dusts generated from milling slags to be recycled into the smelting process or upcycled in a different industry can be carried by the wind, affecting a larger ecosystem. It can be ingested, posing a direct health risk to the communities near the plant, mines, and disposal sites. According to the 2019 International Energy Agency (IEA) report, the iron and steel industry directly contributed 2.6 Gt to global CO2 emissions and accounted for 7% of global energy demand. The IEA report and the WSA project a continual increase in demand in the coming years prompting greater efforts to move toward a circular economy. See also Calcium cycle Circular economy Clinker (waste) Dross Fly ash Ground granulated blast furnace slag Mill scale Pozzolan Slag (welding) Spoil tip Tailings References Further reading Amorphous solids Materials with minor glass phase Steelmaking Smelting By-products