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(Vieira et al., 2007)

Steelmaking results in the production of a range of sludge, dust and filter cake wastes alongside slag. These wastes are produced in a significantly lower quantities than slag, but due to the scale of steel production they can still account for significant material waste streams.

Steelmaking sludge derives from the gas treatment processes used in blast furnace and basic oxygen steel making and is reportedly generated at a typical ratio of 28kg per tonne of blast furnace pig iron and 15-16kg per tonne of basic oxygen furnace steel (Das et al., 2007).

The composition of both forms of sludge are primarily made up of iron, calcium, silicon, manganese and aluminum oxides, with iron oxide content of up to 40% for blast furnace sludge and 70% for basic oxygen sludge (Lobato, Villegas and Mansur, 2015). Given the high iron oxide contents, the primary recycling route for these wastes is directly in the steel industry. However, additional processing stages such as sintering and zinc-removal through leaching, flotation and calcination need to be employed in order to prepare the material in a useable state for steel production (Lobato, Villegas and Mansur, 2015).