Abstract
Despite public concern the overall production of waste materials is still growing all over the industrialised world. This trend is recognised to be correlated to the rate of economic growth (WWF, Living Planet Report 2006) and to tackle this problem and other environmental issues, the European Community recently produced the Sixth Environment Action Programme 2002-2012. The EU approach to waste management is to prioritise waste prevention, followed by waste reuse, recycling, recovery and incineration, and finally, only as a last resort, disposal. The target is to reduce the quantity of waste going to final disposal by around 20% on 2000 levels by 2010 and in the order of 50% by 2050. However, not every waste can be eliminated, reused, recycled, or used as alternative fuel. For hazardous wastes that are to be disposed of to landfill, especially formulated and optimised treatments are required when the leaching properties of the waste materials exceed the actual regulations. Electric arc furnace (EAF) dust is the airborne dust generated in the steel manufacturing process when metal scrap is electrically melted. As a general rule, EAF dust contains significant levels of heavy metals such as Zn, Pb, Cr and Cd, and is listed as hazardous waste with the code 10 02 07* in the European Waste Catalogue. In the UK, EAF dust was disposed of to landfill until the Waste Acceptance Criteria (WAC) was introduced in July 2005 under the Landfill (England and Wales) Regulations. According to current regulations, EAF dust must be treated prior to disposal to landfill in order to reduce the leaching of heavy metals in excess of relevant WAC. Stabilisation/Solidification with cement-based binders is an established technology for the treatment of hazardous wastes, and for the remediation of contaminated soil. The use of cement-based binders, such as Portland cement and pozzolanic materials, provides a low permeable matrix that constitutes a physical barrier to the release of contaminants into the environment. Moreover, the contaminants can be retained either through adsorption onto the cement matrix, through precipitation as metal hydroxides due to the alkaline pH of cement, or through incorporation into the cement matrix. The Centre for Environmental Health Engineering is presently involved in a research project whose aim is to investigate the properties of S/S products obtained by mixing EAF dust with CEM I, ground granulated blastfurnace slag (ggbs), and fly ash from coal fired power generation. Corus - Europe's second largest steel producer - provided a random sample of waste material produced at the site in Aldwarke, Rotherham; while CEM I, ggbs, and fly ash were supplied by Castle Cement, Cementitious Slag Makers Association, and UK Quality Ash Association, respectively. Basic characterisation and leaching properties of EAF dust were provided as required by the WAC. Grout specimens were prepared with waste-to-binder ratios varying from 40% to 90%, the water-to-solids ratio being in the range of 0.35-0.40. Setting time, consistence, unconfined compressive strength, microstructural and leaching properties were evaluated. Stabilisation/Solidification of EAF dust seems to represent a promising process for the treatment of EAF dust prior to landfill disposal. However, further studies are needed to evaluate, optimise and improve the leaching properties of the solidified waste forms.