Slag
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[[Image:Slag2.jpg|right|300px|thumb|A path through a slag heap in [[Clarkdale, Arizona]], showing the striations from the now rusting corrugated sheets used to hold it back.]]
'''Slag''' is the [[by-product]] of [[smelting]] [[ore]] to purify [[metal]]s. They can be considered to be a mixture of metal [[oxide]]s; however, they can contain metal [[sulfide]]s (see also [[Matte (metallurgy)|matte]]) and metal [[atom]]s in the elemental form. While slags are generally used as a waste removal mechanism in metal smelting, they can also serve other purposes, such as assisting in smelt [[temperature control]] and minimizing re-oxidation of the final liquid metal product before [[casting]].
In nature, the ores of metals such as [[iron]], [[copper]], [[lead]], [[aluminium]], and other metals are found in impure states, often [[redox|oxidized]] and mixed in with [[silicate]]s of other metals. During smelting, when the ore is exposed to high temperatures, these impurities are separated from the molten metal and can be removed. The collection of compounds that is removed is the slag. However, in many smelting processes, oxides are introduced in order to control the slag chemistry, assisting in the removal of impurities and protecting the furnace [[refractory]] lining from excessive wear. In this case, the slag is then termed ''synthetic''. A good example is steelmaking slag: [[quicklime]] and [[magnesite]] are introduced for refractory protection, neutralising the [[alumina]] and [[silica]] separated from the metal, and assist in the removal of sulfur and phosphorous from the steel.
[[Ferrous]] and [[non-ferrous]] smelting processes produce different slags. The smelting of copper and lead in non-ferrous smelting, for instance, is designed to remove the iron and silica that often occurs with those ores and separates it as an iron silicate based slag. Slag from [[steel mill]]s in ferrous smelting, on the other hand, is designed to minimize iron loss and so mainly contains oxides of [[calcium]], [[magnesium]], and [[aluminium]].
In some places in northern Michigan, the slag waste was dumped into the water. This combined with such minerals as dolomite and created a glass-like rock that is very attractive. These slag rocks formed green, purple and bright blue mixtures that are often used by local jewelers in jewellery.{{Fact|date=February 2008}}
Slag has many commercial uses, and is rarely thrown away. It is often reprocessed to separate any other metals that it may contain. The remnants of this recovery can be used in [[rail transport|railroad]] [[track ballast]], and as [[fertilizer]]. It has been used as a [[Pavement (material)|road base material]] and as a cheap and durable means of roughening sloping faces of [[seawall]]s in order to progressively arrest the movement of [[wave]]s.
Ground granulated slag is often used in concrete in combination with [[Portland cement]] as part of a blended [[cement]]. Ground granulated slag reacts with water to produce cementitious properties. Concrete containing ground granulated slag develops strength over a longer period, leading to reduced permeability and better durability properties. Since the unit volume of Portland cement will also be reduced, concrete is less vulnerable to [[alkali-silica]] and [[sulfate attack]].
==Basic slag==
Basic slag is a byproduct of [[steelmaking]] by the basic version of the [[Bessemer process]] or the [[Linz-Donawitz process]]. It is largely [[limestone]] or [[dolomite]] which has absorbed [[phosphate]] from the iron ore being [[smelt]]ed. Because of the slowly-released phosphate content, as well as for its [[Liming (soil)|liming]] effect, it is valued as [[fertilizer]] in gardens and farms in steelmaking areas. According to the American Association of Plant Food Control Officials, basic slag must contain at least 12% total [[phosphoric acid]] (P<sub>2</sub>O<sub>5</sub>) or be labeled "low phosphate".<ref>{{Citation | title = Part V - Soil Acidity and Liming | url = http://hubcap.clemson.edu/~blpprt/acid5.html | accessdate = 26-05-2008}}.</ref>
==See also==
* [[Ground granulated blast furnace slag]]
* [[Cement]]
* [[Fly ash]]
* [[Matte (metallurgy)]]
* [[Pozzolan]]
* [[Dross]]
* [[Slag heap]]
==References==
===Notes===
{{reflist}}
===Bibliography===
*{{Cite journal
| last = Dimitrova
| first = S.V.
| date = 1996
| title = Metal sorption on blast-furnace slag
| journal = Water Research
| volume = 30
| issue = 1
| pages = 228–232
| doi = 10.1016/0043-1354(95)00104-S
}}
*{{Cite journal
| last = Roy
| first = D.M.
| date = 1982
| title = Hydration, structure, and properties of blast furnace slag cements, mortars, and concrete
| journal = ACI Journal Proceedings
| volume = 79
| issue = 6
}}
*{{Cite journal
| last = Fredericci
| first = C.
| coauthors = Zanotto, E.D., Ziemath, E.C.
| date = 2000
| title = Crystallization mechanism and properties of a blast furnace slag glass
| journal = Journal of Non-Crystalline Solids
| volume = 273
| issue = 1-3
| pages = 64–75
| doi = 10.1016/S0022-3093(00)00145-9
}}
[[Category:Amorphous solids]]
[[Category:Cement]]
[[Category:Concrete]]
[[Category:Glass types]]
[[Category:Materials]]
[[Category:Soil improvers]]
[[Category:Steelmaking]]
[[bg:Шлака]]
[[cs:Struska]]
[[da:Slagge]]
[[de:Schlacke]]
[[es:Escoria]]
[[fr:Laitier (sidérurgie)]]
[[hu:Salak]]
[[nl:Slak (metallurgie)]]
[[ja:スラグ]]
[[pl:Żużel (hutnictwo)]]
[[pt:Escória]]
[[ro:Zgură]]
[[ru:Шлак]]
[[fi:Tuomaskuona]]
[[sv:Slagg]]
[[uk:Шлак]]