Air- cooling

Process where the slag is allowed to cool slowly by leaving it in contact with ambient temperature air.

AOD Process

AOD stands for argon Argon Oxygen Decarburization, a refining process associated with the production of stainless steel. Most stainless steel is initially produced in an electric arc furnace before being transferred to a separate ladle furnace for refining to achieve the precise metallurgical content required – a process known as secondary metallurgy. In the AOD process, a mixture of argon and oxygen is blown through the molten steel in the ladle furnace, and the oxygen achieves the main objective of oxidizing unwanted carbon in the steel melt. But because the vital and expensive chromium contained in all stainless steels is also prone to oxidation and subsequent loss with the process slag, the argon is introduced to inhibit this reaction.


Basic oxygen furnace

Basic Oxygen Furnace (BOF) - also known as LD-converter- is a steel making furnace, in which hot metal from the blast furnace – with some amounts of steel scrap- is converted into steel. High purity oxygen is blown through the molten bath to lower the carbon content. Fluxes are used to reduce other unwanted elements. Those fluxes combine with silicates and oxides to form liquid slag that floats on the surface of the hot metal.

Blast furnace

A furnace used in the integrated metallurgical process in which iron ore in the form of sinter is melted down under a hot air flow (enriched with oxygen), using coal in the form of coke as a heating and reducing agent in the chemical process. As a result, a liquid hot metal is produced, also called pig iron.

Blast furnace lime

Product from blast furnace slag obtained by milling the slag. As essential ingredients it contains calcium and magnesium silicates as well as oxides and is used as fertilizer.


CBR value

California Bearing Ratio (CBR) value is defined as the ratio of load required to cause a specified penetration of a standard plunger into the sample to the load required to produce the same penetration of same plunger into a standard aggregate sample. It is expressed as a percentage and is broadly used in design of the base and the sub-base material for pavement.

Cementitious property

A property of a material to gain strength when mixed with water. The chemical reaction is called hydration.

Converter lime

Product obtained by milling of basic oxygen furnace slag (BOS) as well as by sieving of disintegrated basic oxygen furnace slag (BOS) or ladle slag from the treatment of non-alloyed steels. As essential ingredients it contains calcium and magnesium silicates as well as oxides and is used as fertilizer.

Crude steel

The term means the first solid steel product upon solidification of liquid steel. Also known as raw steel.



Decarburisation means removal of carbon from iron or steels, usually by heating using water vapour, oxygen and carbon dioxide. This gives a low carbon composition in the outer layers of the steel, and hence a softer surface.


A natural sedimentary rock consisting principally of the mineral dolomite [CaMg(CO3)2]. It is used in the manufacture of cement, as a building stone and as a fluxing agent in the iron and steel making operations.


Electric Arc Furnace (EAF)

An electrical furnace in which the thermal effect of an electric arc is used to smelt materials like steel scrap or iron. Once the furnace is charged and covered, graphite electrodes are lowered through holes in the roof. The electric arc travelling between the electrodes and the metallic charge creates intense heat which melts the charge. Alloying elements can be added during the process.



Ground granulated blast furnace slag.


The vitrification of molten slag by treating with large volumes of (normally) high pressure water. The water both instantaniously cools and breaks up the slag into granules.


Hot metal

Hot, liquid, metallic iron product obtained upon reduction of iron ore in a blast furnace. It proceeds to the basic oxygen furnace in molten form or is cast as pig iron.


Iron ore

An ore from which iron can be extracted. It is the primary raw material in the manufacture of steel. Iron ore occurs in most countries in varying forms of purity. Most iron produced in Europe is made from high purity ores from Australia, South Afica and Brazil which can contain over 70% iron.



A vessel for receiving and handling liquid steel. It is constructed of a refractory-lined steel shell.


A basic oxygen furnace. LD is short for Linz-Donawitz, named after the Austrian towns Linz and Donawitz (a district of Leoben) where the LD-process was developed.

LD process

Linz-Donawitz process which is also known as basic oxygen process. Iron/hot metal which is still molten is transferred from the blast furnace to a large steel making vessel (LD-converter) and scrap steel and lime is added. Oxygen is blown over the metal to reduce the carbon content and specific materials are added to make various types of steel.


Calcium oxide (CaO), a product derived from burnt (calcined) limestone. It is used as a fluxing agent in the iron and steel making operations. The flux, which may also include additions of dolomite or limestone combine with other non-metallic components and results in liquid slag.


A natural sedimentary rock consisting primarily of calcium carbonate (CaCO3). It is used as building stone, in the manufacture of lime, carbon dioxide, cement or as a fluxing agent in the iron and steel making operations.



The MIDREX® Process is a direct reduction process where the removal of oxygen from iron ore occurs without melting. For more information visit



Molten slag is thrown through the air by a spinning drum and water is sprayed into the area from the sides and ceiling of the structure. Both air and water cool the slag. The smaller particles produced are glassy and are suitable for cementitious use. The larger lumps (greater than 10 mm) tend to be crystalline and thus used for aggregate.

Portland cement

A hydraulic cement made by heating a limestone and clay mixture in a kiln and pulverizing the resulting material.


Silicate lime fertiliser

Basic slag from metallurgical processes such as blast furnaces or converters


A slag skimmer is special equipment for separation hot metal from liquid slag. Once the taphole in the blast furnace is drilled open, hot metal and slag flow down a deep trench called a "trough". The hot metal flows through a skimmer opening, down the "iron runners". Since the slag is less dense than iron, it floats on top of the iron, down the trough, hits the skimmer and is diverted into the "slag runners". The liquid slag flows into "slag pots".


Byproduct of ferrous manufacture which is composed of those elements not required in either the molten iron or steel.



Basic slag (Thomas slag) from the "Thomas process", a process of dephosphorisation of pig iron (hot metal), with a phosphate (P2O5) content of 10 - 15 % . Nowadays, the Thomas process is dicplaced by other smelting processes using low phosphate iron ores. Consequently Thomasphosphate does not arise any more.


UVCB Substance

Substances of Unknown or Variable composition, Complex reaction products or Biological materials. For identification and naming in REACH, substances are divided into two main groups: 1. “Well defined substances”: substances with a defined qualitative and quantitative composition. 2. “UVCB substances”: substances of Unknown or Variable composition, Complex reaction products or Biological materials. Variability of composition for well defined substances is specified by the upper and lower limits of the concentration range(s) of the main constituent(s). For UVCB substances, the number of constituents is relatively large and/or the composition is, to a significant part, unknown and/or the variability of composition is relatively large or poorly predictable. As a consequence other type of information for identification is necessary. Those identifiers can be “process related” or “source related”.


VD process

Vacuum Degassing process, a secondary steelmaking operation in which the molten steel is exposed to vacuum. The aim is improve the steel quality by removing gases, improving the steel cleanliness and obtaining a greater uniformity of the chemical composition.


Making into glassy substance by rapidly cooling molten slag. The aim is to minimise crystalline content. Slag for cementitious purposes can only be composed of vitrified (glassy) material.

VOD process

Vacuum Oxygen Decarburization. A refinement of stainless steel that reduces carbon content. Molten, unrefined stainless steel is heated and stirred by an electrical current while oxygen enters from the top. Many undesirable gases escape from the stainless steel and are evacuated by a vacuum pump. Alloys and other additives are then mixed in to refine the molten stainless steel further.

Volume Stability

The ability of treated or weathered slag not to increase in volume by the interaction of water and lime.



Subjecting stockpiles of slag to be exposed to normal weather with the principal objective of getting water to react with calcium oxide inclusions.