This is a followon post to the explanation of how steel is made and why the steel industry is not going to return to Pittsburgh.
Once iron ore is melted, the impurities float to the top. Typically silicone dioxide or calcium oxide are added to speed up the removal of the oxygen, converting iron oxide into pure iron and binding with phosphorus and sulfur
So what do you do with this molten waste that is a mix of silicon, calcium, magnesium and aluminum? You dump it in a field called a slag heap.
So what do you do with a slag heap after you have been dumping slag for 100 years and the steel mills close? After slag cools, it is roughly the consistency of hardened concrete. You cover it with asphalt and build a shopping center on top, or you put down some topsoil and build luxury condominiums.
The slag industry has a trade association