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LD Steel Slag

Definition

Steelworks slags are products resulting from industrial processes aimed at obtaining the hot metal, in the first place, and then the steel. The Steel Slag is generated in the steelmaking process, resulting from the transformation of the liquid hot metal into steel. The acronym LD is due to the fact that the steel is produced in a LD type oxygen converter.

In the process of steeling or refining, the percentage of carbon is controlled and the excess of impurities is eliminated so that to guarantee the quality of the steel. For this purpose, the metallic charge in the converter (liquid hot metal and scrap) receives additions of materials called fluxes, which are responsible for the fixation of the oxides formed during the reactions.

The main fluxes are lime (CaO), and fluorite (Ca F2), whose function is the fixation of formed oxides. The melting and refining of the charge are processed through the oxidation reactions of the impurities present in the steel such as, silicon (Si), phosphor (P), sulfur (S), manganese (Mn) and through the reduction of the carbon content. These formed oxides combine with the dissolved CaO and form a slag that is stable and different from the metal bath.

The liquid steel and the resulting slag stay separated inside the converter due to the density difference. This aspect is used as an advantage to withdraw them from the converter separately: the steel is put in a suitable ladle and the slag goes into a "cinder pot" (a container of cast steel that is transported through a railway). However, inside the cinder pot there is still around 6% of free metal weight (FeO) mixed with the slag. After this slag has been processed, the cinder pot can be reutilized. Currently, ArcelorMittal Tubarão produces around 86.2 kg of slag/t of liquid steel, which results in approximately 415.000 t/year.

Processing

After the liquid slag is withdrawn from the converter, with a temperature of around 1400º C, it is transported to the slag yard, where it is tilted in suitably prepared sections.

The process consists of cooling the slag and submitting it to an appropriate crushing mill, where the metallic fraction is separated and the resulting slag is classified in commercial granular ranges.

In order for the slag to be processed, it needs to be cooled first. Upon being cooled through thermal shock by using water jets, the slag undergoes a fragmentation in blocks, then generating a material defined as Raw Steel Slag.

ArcelorMittal Tubarão commercializes part of this material, which is called LD NP Steel Slag, and has a granular range between 0 and 500 mm.

After cooling, part of the Raw LD Steel slag is processed at a crushing and screening mill, where both the metallic fraction and the slag are separated and classified. This crushed slag, which is separated according to its granulometry and then commercialized by ArcelorMittal Tubarão for several applications - the so-called Steel Slag In Natura, is that one coming from the Steelmaking Plant, already crushed and screened, but not submitted to expansion reduction treatment. While being used in any application, this material cannot be confined due to its volumetric expansibility.

Since 1999, Companhia Siderúrgica de Tubarão has achieved technical developments in partnership with a road consulting firm, Kaeme Consulting Ltda, from Vila Velha city, with a view to correct the main problem that arises from the utilization of the Steel Slag - its expansion through the reaction of free oxides, calcium and magnesium, and the free CaO and MgO. The process developed by ArcelorMittal Tubarão and Kaeme, inside ArcelorMittal Tubarão plant, allows the free oxides to become partially inert, reducing the slag's expansion capacity, and then making it feasible for applications such as Road Construction, either sub-base or base, or even for producing asphaltic coating, the CBUQ. Upon reaching a satisfactory expansion rate in accordance with the technical standards, the process is interrupted and the material is made available to the market as the so-called ACERITA (Steel Slag with Expansion Reduction).

Chemical Composition (Reference)

ELEMENT	LD STEEL SLAG
Calcium Oxide	23-46
Magnesium Oxide	5-13
Silicon Dioxide	11-15
Aluminum Oxide	0,8-4
Total Iron	14-22

Main Properties

PROPERTIES	CORRESPONDING APPLICATIONS
Compressive / load resistance	Concrete Asphalt Railway ballast Bases for roads
Long lasting resistance	Concrete Asphalt Railway ballast Bases for roads
Free draining	Railway ballast Bases for roads Soil preparation
Interconnected angular particles	Concrete Asphalt Railway ballast
Skidding resistance	Concrete Asphalt
Inertia	Bases for roads Soil preparation
Basicity / CaO content	Cement Agronomical use
Content of soluble P2O5 solúvel	Agronomical use Fertilizers

Environmental Aspects

Studies carried out

• Metals contained in the slag do not leach easily in substantial quantities of ground or surface water, therefore, they pose little or no concern regarding the quality of drinking water.
• Slags do not cause any impact on animal life or other forms of life on the lands where it is applied. Metals contained in the steel slag do not bioaccumulate in the soil.
• The Steel Slag can be applied safely in aquatic environments such as, rivers, lakes and streams, without impacting the quality of the water or aquatic life. Such aquatic environments allow for sufficient dilution (at least 1000 times), which protects against significant pH changes. Care should be taken while applying the slag on smaller aquatic bodies with low conditions of water flow, such as soaked soils or shallow canals.
• The risks related to health and associated with steelworks slags are neither significant for urban and rural populations nor for the potentially exposed workers involved in maintenance, industry and construction.
• The slag utilized for making cement partially replaces the clinker thus reducing the consumption of energy and the resulting CO₂ emissions
• The impacts on the environment brought by the extraction of minerals may be eliminated by using slag.
• The Steel Slag analyzed by X-ray diffraction did not reveal any content of crystalline silica (blasting of structures).

Applications

• Base and sub-base of road pavements;
• Road drains;
• Primary layers for yards;
• Asphaltic coating;
• Agricultural corrective (conditioner);
• Rip-Rap embankments;
• Concrete;
• Anti-dust treatment;
• Blasting of structures;
• Rock Plugs;
• Recycling in steelworks processes;
• Landfills;
• Cement;
• River banks;
• Railway ballast;
• Treatment of acid waters

For further information, please check these links:

Railway Construction
Road Construction
Civil Construction
Agriculture
Blasting

Researches

ArcelorMittal Tubarão continues searching for new market alternatives for the Steel Slag, aiming at its stability, with a view to provide and guarantee an increasingly high quality in the application of this co-products. Then we undertake a great deal of investments in research by establishing partnerships with several important institutions, such as:

• NEXES (Núcleo de Excelência de Escórias Siderúrgicas - Research Center for Steelworks Slags): Established at the Technology Center of the Federal University of Espírito Santo - UFES, its purpose is to undertake researches for the potential utilization of slags and engender increasingly developed markets for slags and other steelworks co-products. Its main target involves the research and further transference of know-how aimed at developing the market for co-products, besides searching for the standardization of their applications. Among these projects, are the assessment of expansibility and treatment technologies aiming at developing the market for Steel Slags (AGSPAVI) as well as the assessment of environmental aspects, cost, resistance, and durability of pavements built with Steel Slag (PAVIAMB).
• DNIT / KAEME: With a view to continue the partnership that resulted in the development of ACERITA and at the same time searching for a partnership with federal agencies responsible for the standardization of road construction, ArcelorMittal Tubarão has signed an agreement for developing researches on the application of steel slag and other co-products in road construction. The bottom line is proving the quality and agreement studies of the existing standards for spreading this technology through the responsible federal agency.