After having gained an overview on the production of steel slag in Europe and the average composition of slags, different concepts to treat steel slags have been proposed (Task 1).
To evaluate the treatment measures the European legislation on environmental demands have been investigated and evaluated (Task 2).
The treatment methods have been transferred into operational practice:
Treatment beyond from the steel making process:
Steel slags from high alloy (stainless) steelmaking (Tasks 1 - 6) have been reduced in a DC-EAF. As a result the critical chrome content has been reduced totally from the slag. After modifying the slag's composition the slag can be used as air-cooled slag in road construction or as granulated slag as raw material for cement (like granulated blast furnace slag). The technical application of the process has to be proved.
The main problem of slags from carbon steel making is their lack in volume stability. Various solutions are proposed to solve this problem:
VASL has investigated the use of dusts in BOF steel making and the effects on steel and slag quality, as well as the effects on the dust composition (Task 8).
In Germany the treatment of slag depart from BOF steel production has been developed. As a result a treatment process has been constructed in one of the steelworks. In this process slags are treated with sand and oxygen to bind the free lime into stable slag phases.
Another treatment is proposed by the partners from Belgium and Luxembourg: The addition of glass cullets, which contain also silica to bind the free lime. But this material is cheaper than the sand due to a strong environmental initiative to find recycling routes. The product glass cullets cannot be recycled into the glass furnace since it does not fulfil the specifications on the raw material "glass cullets" used in flat glass furnaces, due to lining enamels, etc. contained in such glasses. The glass cullets are introduced directly into the steel making furnace after steel removal or crushed and injected together with oxygen into the slag pot. This second method is similar to the German process of sand injection.
The slags fulfilled all technological demands and environmental requirements.
The following applications are tested:
Use of the slag as armourstones on embankments in waterway construction.
Use of the slag as aggregates in road construction.
Use of slag as aggregates in low noise asphalt layers on roads.
Use as aggregates for lean concrete in road construction as well as for concrete paving stones.
Test fields have been constructed to demonstrate the excellent properties under actual conditions.
Furthermore the use of residues from iron and steelmaking together with residues from coal combustion as refilling mixtures for mining shafts have been investigated.
The evaluation of the technical feasibility of the processes has shown that it is possible to produce volume stable steel slags with good technical properties fulfilling the demands of European and national standards. The environmental requirements are fulfilled concerning to the European and national legislation, but sometimes the actual treatment of the liquid slag with glass cullets has not been satisfactory concerning to their volume stability, and therefore needs further improvement.
A final evaluation on the economics of the treatment process is in progress.
From the point of view of the proposed research all expected results have been achieved. Some of the treatment methods are put into operational practice, already.
Besides of the slag there are some other residues from steel making which should be used as refilling materials for mining shafts. Several residues have been investigated in order to find suitable components for refilling mixtures. Finally mixtures have been investigated that have been prepared from dusts from blast furnace operation, e.g. casting bay degassing, sinter plant, blast furnace sludges, dust from ladle degassing and dust from coal combustion. After testing these mixtures in laboratory, the most suitable mixtures have been tested in lysimeter test fields. However, after one year of testing, the results have not shown the expected results, Task 14. Further investigations are necessary.
There is a great demand for aggregates for different applications in civil engineering. In Germany about 88% of these aggregates are reclaimed from natural stone. On the other hand in the steel industry considerable amounts of steel slag will be produced which can be used as aggregates in special fields of applications in civil engineering if they satisfy the demands on volume stability.
The target of this research proposal is to treat steel slags with various residues from other industries as well as residues originating from steel making, to improve the volume stability of the slags. Using residues from various industrial production will bring advantages to the target to "zero waste" steel making and will also improve the economy of the treatment process.
The production of steel slags with sufficient volume stability will bring benefits to the SME organized slag processors who will improve their economy.
The problem of recycling the steel slags into high quality
applications will be advantageous to all European countries.
Funding SchemeCSC - Cost-sharing contracts
971 87 Luled
971 25 Lulea
47809 Krefeld - Rheinhafen