Iron & Steel Industry Slag Types

TRS use in-house techniques to identify the various slag types encountered in iron and steel making operations.

The processes of iron and steel manufacture give rise to various by-products, some of which are slags. The latter can be described as non-metallic products of metal production and include:

Blast Furnace Slag
Basic Steel Slag
Acid Steel Slag

Blast Furnace Slag
Blast furnace slag can be broadly divided into two main categories:

‘Basic’ iron-making slags which constitute virtually all current production.
‘Hematite’ blast furnace slag derived from the use of ‘hematite’ iron ore and generally native to the NW of England.

Blast furnace slag, when properly utilised, can be an excellent source of constructional material, finding applications in roadstone, concrete aggregate, biological filter media, glass making, cements, etc..

In addition to work on existing and new slag based products, TRS has carried out significant work to utilise old, stockpiled blast furnace slag material. Such work has led to the re-utilisation of several million tonnes of slag, previously considered unusable.

Basic Steel Slag
Basic Steel Slag is the product of steel making using ‘basic’ fluxes, i.e. high in Ca0 and/or Mg0. Virtually all modern steel making operations are ‘basic’ processes, and much old steel making slag also falls into this category. Basic steel slag, both old and new, is under-utilised compared to blast furnace slag. This is partly due to problems of volumetric instability, attributable to the delayed hydration of free lime and/or free magnesia commonly present in this slag type. Nonetheless, excellent products can be produced for specific markets in road making applications. However, appropriate informed processing is required to produce satisfactory, high quality products.

Acid Steel Slag
Acid Steel Slag is now relatively rare and is encountered mainly in old slag deposits in the UK. They contain no free Ca0 or Mg0 and are generally accepted as being volumetrically stable.