Experimental analysis on the use of BF-sludge for the reduction of BOF-powders to direct reduced iron (DRI) production

• Blast furnace sludge contains a valuable residual fraction of carbon coke.
• Blast furnace sludge was used as a reducing agent for BOF oxidized powders.
• Self-reducing pellets were produced by mixing BF-sludge with BOF powders.
• The pellets were reduced in both air and argon.
• The pellets reduction leads to iron production via direct reduction.

Approximately 25 Mt/year of sludge and dust are obtained from the treatment of the exhaust gases produced during the manufacturing of cast iron and steel from blast furnace, converter and continuous casting machines. This waste contains a large amount of valuable elements that could be recycled in the steelmaking process itself. Unfortunately, sludge and dust are difficult to recycle and so most of them are disposed in landfills. In this work, a feasibility study on the use of blast furnace sludge as a reducing agent to produce direct reduced iron from BOF-dust is presented. Self-reducing briquettes containing a mixture of BOF-dust, BOF-sludge and BF-sludge were produced. Thermo-gravimetric and roasting tests were performed in non-isotherm conditions from room temperature to 1170 °C in both argon and air atmospheres. The XRD and SEM analysis performed highlighted the metallization ratio of about 50–60% for air reduced briquette and 60–80% for argon reduced briquette. These results foster the technical feasibility of the use of BF sludge as a reducing agent to produce direct reduced iron (DRI). The use of BF-sludge as C-source for BOF dusts reduction lead to a cost saving estimated to 1500 M€/year worldwide.