ROBERT BROOK / SCIENCE PHOTO LIBRARY ROBERT BROOK / SCIENCE PHOTO LIBRARY
Industrial waste. Slag from a steelworks. Slag is the waste product from the production of iron in a blast furnace. It consists of impurities from the iron ore (such as sulphur), but it mostly contains melted limestone (a raw material added to remove the sulphur from the iron ore), plus other oxides from the iron ore, such as aluminium, silicon and magnesium oxides. The slag floats on the liquid iron and is diverted to a dump while the iron is retained. When cool, as here, it can be processed into building materials for roads or foundations for railways. Photographed at a disused steelworks on Teesside, Cleveland, UK.
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