Hydrocyclone Processing of Blast Furnace Slurry

The high levels of iron and carbon present in blast furnace slurry would make it an attractive material to recycle if it were not for the levels of tramp elements which it also contains. It is because of the levels of these "tramp" elements that until fairly recently Corus has always transferred this material to internal landfill sites.

The system developed by Corus (shown schematically) employs a single stage treatment (unlike several other systems currently available). The use of costly slurry drying equipment has also been avoided resulting in overall lower capital, operating and energy costs.

Hydrocyclones are used for stream separation in many industries. Subsequently Corus believed that this technique could be suitable for the removal of zinc and other heavy metals from the various slurries arising in an integrated steelworks. Laboratory testwork, carried out on the apparatus shown to the left, was quickly followed by a pilot scale trial at Scunthorpe Works, the positive results of which, led to the construction, commissioning and operation of full scale hydrocyclone plants at Llanwern and Teesside Works designed to treat all of the arising by-product.

Results indicated that the ZnO in the slurry could be reduced from 2.7% to 0.4%. The fraction of material recovered for recycling was found to range between 70% - 80% of the solids arising. The results also demonstrated that approximately 88% of the ZnO could be removed in only 28% of the solid material.

Benefits to be gained from the introduction of hydrocyclones include:

• The intrinsic value of the recovered material ($15-50$/t) when recycled
• A considerable reduction in landfill quantities (70 to 80% at BS sites) with associated reductions in costs and taxes
• Benefit to the environment - reduced waste
• Can be easily fitted retrospectively