Beneficiation of BOF-slags by mineral processing for enhanced application in road construction

Blast oxygen furnace slag (BOF) is one major by-product of steel production by Linz-Donawitz process. It is produced in the converter during the refining from pig iron to crude steel. At HKM steel plant approximately 430.000 t of BOF slag is produced ongoing the production of 4.3 Mio. t of steel, annually. Nowadays 30.000 t of the slag is used as high-quality asphalt chippings. BOF consists in general of Ca-silicates, Ca-ferrites and Fe-oxides. The slags show further a wide variety in specific gravity due the randomized distribution of macro porosity and heavy steel particles.

One limiting factor for this application is the homogeneous specific gravity of the material, which is crucial because it controls the asphalt recipes. However, bituminous binder is one major cost factor during asphalt production.

In this study, we present a combination of analytical procedures to investigate the distribution of pores and steel pebbles in slag particles to evaluate the particle specific gravity. Based on the analytical results, a beneficiation scheme by mineral processing is presented to separate heavier from lighter particles. As an established method of gravity concentration, jigging is used as a reference. In addition, the application of sensor-based sorting using X-ray transmission technology is presented for density-based separation.

By the application of the presented processing scheme, the BOF slag´s variability in density can be reduced to a tenth of its original deviation. Thus, the presented beneficiation scheme is capable to improve BOF slag valorization due to improved value.