Slag
Slag referred to in metallurgy a glassy or crystalline melting solidified residue nonmetallic Art It is a mixture of substances, which is composed of basic and acidic oxides. It is produced during the extraction of metals in ore smelting and has massive to porous properties. The term slag has developed at the beginning of ore smelting, since at this time the non-metallic residue were separated by hitting the metal. (see also: sponge iron to the historical production of iron )
Slag is, if it is not brought to a landfill, mainly used as a secondary raw material in the construction industry as an additive for cement or as aggregates for base courses.
Formation
Slags arise in almost all metallurgical manufacturing and treatment processes. In the smelting a homogeneous slag layer ( so-called slag ceiling) is formed as a result of their lower density on the metal. The slag is separated in the melt flow from the metal and then poured in the liquid state to cool in so-called beds. From there it enters the treatment plant, where then takes crushing and sieving of the slag according to the intended use.
Species
The product metals of metallurgical processes are contained in the slag only to a small extent. A distinction is made between the following types:
- Blast furnace slag (short HOS ) is due to aggregates of the production of pig iron in the blast furnace.
- Steel slag or converter slag (short SWS or LDS) from the aggregates of the production of steel from pig iron comes from the steel mill.
- Electric furnace slag (short- EOS ) is due to surcharges the smelting of steel scrap in electric arc furnace.
- Stainless steel slag (short EDS ) come from the aggregates of the refining of steel alloys to stainless steel.
- Ferrous slag (short MHS) comprises slag from the aggregates from copper smelting, zinc, lead and chromium ore with iron as metal exchange.
Use
Homogeneous waste incurred in larger amounts, serve as a secondary raw material, different products can be made from the. This is useful because the landfill areas are limited and costly, and natural resources.
Thus, for example, serves granulated blast furnace slag ( granulated slag ) finely ground as a component of various types of cement. Furthermore, for the production of slag mineral fertilizers used. In road construction may granulated slag such as slag, gravel, slag, crushed stone, slag, gravel and excavator slag, consisting of unsorted ironworks or smelter slag, are incorporated as aggregate in unbound base courses. In paving, so-called cinder blocks can be used with fixed block formats. With a density of 2800 kg / m³ to 4000 kg / m³ massive slag is at least as hard as granite. Slag, which has included air during solidification, however, is much easier. By the end of the 19th century Traunstein and Berchtesgaden houses were built of breeze blocks in today's counties, as these by the contained air pockets a similarly good thermal insulation characteristics as the Bauziegel used today and also look very attractive. These came decommissioned from the mid-20th century iron ore mine in the Ach Valley near Neukirchen (now Teisendorf market town, county BGL). In addition to many farmhouses still exist larger building cinderblock, such as the Bergen / Upper Bavaria station. on the railway line from Munich - Salzburg, or the 1912 decommissioned Saline in Traunstein.
In older homes that were built in the vicinity of iron works, slag often came as an insulating material used. During renovation work, this can be disposed of in many regions as building rubble.
Industrial slag is also referred to as rock or iron silicate and iron silicate is used as blasting material in the blasting art.
HO and LD slag
In the steel mill process of an integrated steel plant blast furnace slag fall (HO) and steel slag (LD). Steel slags are also referred to as LD slag, since they are obtained from the melt of Linz Donawitz (LD ) steel production process. While slags are granulated from the blast furnace processes today in large part to blast furnace slag, LD slags are processed into various products. Depending on the hardness of the LD slag are to be processed ( with low lime content ) or can these fertilizers suitable as road construction materials. However, in autumn 2012 the Austrian Umweltdachverband presented a study that suggests the slag a health hazard. If this study acknowledged slag may not be processed and will be deposited charge.
As a result, a study or analysis was commissioned by Greenpeace Austria and ASFINAG the Federal Environment Agency, which resulted in totally safe levels, which amount to only a fraction of the applicable limits.
Designation
Caked with iron slag residues is also referred to as a bear.
An important parameter in metallurgical slags is called the basicity. Thus, one can divide the slag in acidic or basic slag.
Conservation
Slag contain heavy metals in different concentrations. The environmental behavior of slag must therefore be classified as safe before further use and is being investigated for this purpose with the help of Eluattests on its leachability out. Particularly when storing at the landfill or use in construction, for example in road construction has been shown that the long-term behavior under the real conditions of atmospheric gases can not be adequately assessed with the usual Eluattests according to the rules of the Regional Working Group on Waste (LAGA). In slag dumps it often comes to significant localized heating by chemical reactions and the roadbed to leaching due to corrosion and other weathering phenomena, which can lead to pollution of groundwater. For this reason, the use of slag as a building material in drinking water protection zones I and II is not permitted.
Norms and Standards
- DIN 4301 - iron and steel slag and smelter slag in construction
- Leaflet on the use of iron and steel slags in road
- Leaflet on the use of metal and steel slags in road
- Leaflet on the use of blast furnace slag in antifreeze and gravel layers
- Leaflet on the use of metallurgical mineral mixtures, secondary metallurgical slag and steel slag in road construction