Effect of water-powder interaction on the mechanical and metallurgical behavior of integrated steel plant byproducts agglomerates

In 2023, 1888 Mt of steel were produced worldwide, with 70 % via integrated cycle steel plant, generating 34 Mt of dust and 25 Mt of sludge. These wastes are rich in Fe and C but are too fine for direct recycling. Agglomeration is therefore essential to recycle them as suitable feedstock. This work studies how water–powder interactions affect the mechanical (impact resistance, cold compressive strength) and metallurgical (degree of reduction, swelling) properties of self-reducing briquettes made by combining two iron-bearing dusts (BOF dust and a secondary dust) with two reducing agents (BF sludge and another secondary dust) to form hydrophilic–hydrophilic, hydrophobic–hydrophilic, and hydrophobic–hydrophobic mixtures. Water expelled from hydrophobic dust acts as a lubricant during compaction, reducing surface cracks and enhancing eight times the impact resistance. Hydrophilic particles, however, lower impact resistance (failing 10-drop tests) due to hydration repulsion that weakens the briquette. While water absorbed by hydrophilic powders forms gasification channels on drying, enabling a reduction degree up to 94 %, it also causes severe swelling below 1200 °C. The best overall performance was achieved by a hydrophobic–hydrophilic combination with double water content, yielding compressive strength of 18 MPa, degree of reduction of 91 % and swelling of −1.86 %.