Upgrading the value of BOS slag by addition of difficult to recycle glass or slags

Steelmaking slag from the integrated route, ie made from blast furnace hot metal, is demetalled, crushed and screened, and used to create tarmac for the top surface of roads. Its rate of arising in the UK is around 500ktpa. However, it's skid resistance is not high enough for the top grade of road surface. For these locations, virgin aggregate has to be imported with its associated quarrying and transport environmental impact. Modifying the slag to increase the silica content after it is tapped from the steelmaking vessel should improve its skid resistance to the level required for the top grade of road surface. The slag modifier could be slags arising elsewhere in the process route, such as desulphurisation slag, for which there is no ready use. Other likely sources of modifier are certain streams arising from the glass industry, including waste streams contaminated by aggregates, mixed colours, and fines, which cannot be returned to the process, and high silica arising refractory waste. Thus this project objective is to use slag arising within the steel industry, and streams of waste glass and refractory from the glass industry, all of which have no ready recycling route, to modify the slag from the steelmaking process. This will then produce an aggregate replacement of higher value.

The project will make a number of new slags, at the kg scale, by taking existing steelmaking slag and modifying with a number of alternative high silica sources. Thermodynamic modelling will be used to define the mixtures to achieve the aim mineralogy. The slags will be tested to assess the improvement in skid resistance and abrasion resistance. The most promising blend will be produced in a full scale plant trial and will then be further tested. Any field trial of the new slag, ie a trial road surface, must fall outside the project due to the cost and timescale.

The second activity of the project is to undertake a detailed assessment of the volumes and values of waste, or difficult-to-reuse, streams of appropriate material from within the glass industry and the steel works to determine the potential for use as a slag modifier.