GAME CHANGING PROCESS
Steel scrap is recycled in electric arc furnaces by a simple remelting process. Steel production by this method accounts for about one third of global steel production annually.To protect them from corrosion, steel objects are increasingly galvanized which involves the object being coated by a thin layer of zinc metal. As more steel is galvanized so too scrap contains an increasing amount of galvanized material. When the scrap is recycled, the zinc from galvanising, together with other base metals, alkalis and halides, are driven off as a dust and caught up in the flue gasses. These fine particles need to be filtered out before the furnace gasses can be discharged to the atmosphere. The filters are periodically cleaned and the resulting dusty material is known as electric arc furnace dust or EAFD.
For every tonne of steel produced by recycling there are typically between 12 and 20 kg of EAFD produced. EAFD. The EAFD typically contains 18-24% zinc which is 4-5 times the the average zinc deposit found in nature. In addition to zinc the EAFD contains 22% to 30% of iron and 1% to 3% of lead.
Generally speaking at historical zinc prices, the recovery of zinc from EAFD has not been possible without a subsidy, ie it has no value and is therefore considered to be a waste. Since it also contains traces of toxic elements such as cadmium, arsenic and mercury, it is classified as a hazardous waste. EAFD has been processed for many years using Waelz kiln technology but this does not recover the iron, so the residue from the process is still a waste that is classified as hazardous in some countries.
Since the cost of landfill in many countries is less than the subsidy required to justify the development of a Waelz kiln, the EAFD continues to be landfilled in countries where landfill is cheap, ie the developing world. Currently it has been estimated that there are about 7 million tonnes of EAFD generated annually, of which about half is recycled. Assuming that the EAFD has a grade of 22% zinc, over 1.5 million tonnes of zinc is available annually in EAFD which compares with current global consumption of about 13 million tonnes, it is therefore a significant figure in terms of global resources.
The company’s management recognized that a technology that recovered all of the zinc and iron, was energy efficient and generated no waste would enjoy substantially higher margins than existing recyclers, and represent a quantum leap forward environmentally. It would therefore be able to be developed without relying on a substantial subsidy from the EAF operators. An EAFD treatment process that does not require a subsidy will dramatically change the structure of the industry, preclude the requirement for landfill and significantly increase the global proportion of zinc recycled on an annual basis. It will therefore be “Game Changing”
Numerous technologies were considered but the rotary hearth furnace was very clearly the most attractive technology, both environmentally and economically, as it fulfilled all the criteria above.