Iron is produced in large blast furnaces. In the process,"off gases" are generated which contain particles with a significant iron, zinc, lead and carbon content. These are removed from the gas by wet "scrubbers" which produce a watery slurry containing the particles. In the past, the high zinc content meant that the slurry could not be re-used because the zinc would prevent the furnace from working efficiently. So, even though the iron and carbon was useful, the sludge was carefully disposed.

Corus UK have developed the use of hydrocyclones which can separate the iron and carbon particles from the unwanted zinc. The watery sludge is forced into the hydrocyclone cylinder under pressure and this causes it to spin in two opposing vortices. The larger particles, containing iron and carbon get pushed outwards while the smaller zinc particles are channelled towards the centre.

Particles rich in iron and carbon emerge from the bottom of the hydrocyclone and are re-used to feed the furnace.

Corus UK now recycle 70% of these particles and saves £700,000 per year in raw materials and disposal costs. Currently an estimated 5.2 million tonnes of furnace gas dust is produced each year by steel manufacturers throughout the world. The global application of hydrocyclones would enable 3.6 million tonnes per year to be recycled