Page 197 - New Trends in Eco efficient and Recycled Concrete

Steel slags
7

1
2
1
Carlos Thomas , Julia Rosales , Juan Antonio Polanco and
Francisco Agrela 2
1
LADICIM (Laboratory of Materials Science and Engineering), University of Cantabria,
2
E.T.S. de Ingenieros de Caminos, Canales y Puertos, Santander, Spain, Construction
Engineering Area, University of Cordoba, Leonardo Da Vinci Building, Rabanales
Campus, Cordoba, Spain

7.1 Steel manufacturing

The steelmaking industry is one of the most important industries in the world.
According to the World Steel Association (2018), since 2010 more than 1500 mil-
lion tonnes of crude steel were produced annually worldwide; 10% corresponds
with the production of the European Union (28 countries), and the demand for
crude steel is increasing.
Basically, there are two types of technologies used to obtain crude steel. The
first, and the most widespread, uses natural resources from iron mining. The second
technology recycles scrap from the industry or out-of-use steel components. The
crude steel industry produces blooms, billets, slabs or plates that are transformed
through mechanical processes into rails, structural elements, bars, sheets or wires.
Iron ore-based steelmaking accounts for more than two thirds of the production
of crude steel in the world. In this process, iron ore is reduced to iron by mixing it
with coal/coke and limestone in a blast furnace (BF). In the second step, the iron is
converted into steel using a basic oxygen furnace (BOF). One-third of global steel
production uses scrap-based steel. This technology recycles steel in an electric arc
furnace (EAF) using electrical energy to produce an electric arc to melt the scrap.
In some plants other sources, such as metallic iron, are used. After the EAF, the
steel is put though a ladle furnace (LF) to refine the molten steel in order to obtain
different qualities of steel.

7.1.1 By-products of steel manufacturing
About 90% (by weight) of solid by-products that come from iron and crude steel
production are slags. Other by-products are gases, dusts and sludge. The composi-
tion of the slags includes silica, calcium oxide, magnesium oxide, aluminium and
iron and are the result of removing impurities from the molten steel. According to

New Trends in Eco-efficient and Recycled Concrete. DOI: https://doi.org/10.1016/B978-0-08-102480-5.00007-5
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