Steel slag recycling in clay brick production

The feasibility of steel slag recycling in clay bricks was assessed through both laboratory tests and industrial trials on three different typologies of wastes and clay bodies. Important requirements are the slag size, that must be previously ground below 3 mm, and the magnetic susceptibility of waste - connected with the occurrence of magnesioferrite and steel residues - that must be as low as possible to avoid occlusion of electromagnets and extruder die. After firing, the slag is actually inertised, as no significant effect on soluble salts and elution was found; in particular, there is no indication of Cr6+ or Ni2+ mobilisation from clay bricks. The use of slag is substantially possible for additions of 2-3 mass-% without any particular hindrances of technological nature. Additions of up to 5-6 % seem to be practicable, despite a porosity increase and a reduction of the mechanical properties of both unfired and fired products. Larger amounts of slag are decidedly inadvisable due to detrimental changes in the chemical and physical characteristics of products.