Slag is a product of the steel making process. Once scorned as a useless byproduct, it is now accepted and, often, preferred and specified as it is known to be a valuable material with many and varied uses.

 

The composition and nature of the slag is essential to steel making. The addition of limestone/dolomitic stone in its natural form or calcined form, to the iron and steel production process removes the majority of the gangue in the slag.

 

SLAG is a broad term covering all non metallic co products resulting from the separation of a metal from its ore, Its chemistry and morphology depends on the metal being produced and the solidification process used. Slags can be broadly categorized as ferrous (iron/steel) and non-ferrous (copper, lead/zinc) depending on the industry from which they come. Non ferrous slags make up only 12% of the total annual production Described below are the main types and uses of slag commercially available in Ferrous Slag products

 

Iron Blast Furnace Slag (BFS)

 

This is the co-product from the reduction of iron ores to produce molten iron and molten slag.

 

1. When allowed to cool slowly to a crystalline rod< form It becomes a light gray vesicular rock known as Air-Cooled Blast Furnace Slag. Principle uses include:

 

  • Uncrushed - fill and embankments (particularly areas subject to severe loading such as mainline rail systems), working platforms on difficult sites pavements, where binding fines are produced by rolling to break the slag down to fill the voids.
  • Graded road base - on its own or blended with other slags and/or with other natural rocks and sands.
  • Crushed and graded - for concrete aggregates, concrete sand, glass insulation wool, filter medium, and use under concrete slabs as a platform

 

2. By passing the molten slag through high volume high pressure water sprays, a glassy, sand-Type (granulated) material Is formed, known as Granulated Blast Furnace SIag.The color of this product is very similar to normal beach sand.

 

  • The principal use is as Cement replacement (when ground), replacing 30-50% of Portland Cement in 'normal' concrete, but can replace up to 70% in specialist applications such as marine concrete.
  • Other uses include, glass making, trace elements in agriculture, concrete block manufacture, sporting field sub-base (for drainage), filtration medium, reinforced earth embankments, and mine backfilling and grit-blasting medium requiring fine etching.

 

Basic Oxygen Furnace Steel Slag (BOF or Steel Furnace Slag)

 

This slag Is formed when molten Iron, scrap metals and various fluxes, such as lime, are oxidized by injecting large amounts of pure oxygen into the molten iron mix to create molten steel and molten slag. Slow cooling of the molten slag produces a dense rock material. Principal uses include:

 

  • Blending with many other products such as granulated slag, fly ash and lime to form pavement material
  • Other uses Include, skid resistant asphalt aggregate, rail ballast asphaltic concrete aggregate, soil conditioner, hard stand areas and unconfined construction fill.

 

Electric Arc Furnace Slag (EAF or steel furnace slag)

 

Produced when scrap metal and fluxes are oxidized by the use of an electric current. Molten slag is generally placed into ground bays for cooling. Both BOF and EAF slags are somewhat heavier than Blast Furnace Slag and most quarried rock material. Uses include

 

  • Blending with many other products such as granulated slag, fly ash and lime to form pavement material, skid resistant asphalt aggregate and unconfined construction fill.

 

 

 

For more information on iron and steel slag and other mineral resources, visit: minerals.usgs.gov/minerals/

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