Mining operations and the subsequent smelting and refining procedures result in large quantities of waste and by-products. After separating the valuable components, side components and impurities are bound in an artificial rock matrix, the slag, with elevated technical properties, which render them - in principle - feasible for constructive purposes.
However, slags from the Electric Arc Furnace contain, like slags from other processes and also natural rock material, a variety of trace elements, which can give rise to contamination of soils, lakes, rivers and coastal areas, at a certain level of release of these elements from the solid slag. The assessment criteria of the environmental impact at a material based level is often settled on leaching tests.
Electric arc furnace slags from two different production cycles in the same factory have been investigated with the one stage batch test according to EN 12457-4 at a liquid to solid ratio of 10 l/kg after prior aging for a total of three month in ambient, humid and aqueous conditions. Extractions were done at the freshly sampled slag from the factory and at intermediate steps at the age of 21, 42 and 91 days of aging. Their mineralogical composition was determined by a non-quantitive diffraction analysis and the influence of particle size distribution within the sample was evaluated.
The two investigated slags did not show relevant differences in their leaching behaviour, neither does their mineralogical composition, although differences in the content of Wüstite and Gehlenite are observed.
The Barium release of the material stored in ambient and humid conditions showed the expected decrease due to formation of Barite, whose tendency can be mathematically expressed as an exponential-3 parameter-fall, although this is only fulfilled for one of the two slags investigated. In aqueous conditions, the release is slightly higher and does not reveal a definite depletion.
Chrome, Copper, Lead and Zinc showed a similar up and down release tendency during the aging in ambient and humid conditions, which lacks of further explanation. During the storage in aqueous conditions these elements reveal a general peak at the age of 21-42 days, followed by a decrease in release at the final extraction at the age of 91 days, what can probably be associated to the lower reduction potential at the end of the experiment.
Molybdenum appeared not to be influenced by neither of the aging methods applied, its release in both experiments did not show deflection in the time series established.
Vanadium was increasingly released after the aging in ambient and humid conditions, rising its leachability from 0,88mg/kg solid mass for the freshly sampled material in the factory to 1,58mg/kg after 91 days of aging and from 0,58 to 1,13mg/kg respectively.
Comparison regarding the particle size distribution showed a higher release tendency for the finer graded samples, this is more obvious for the anions than for the cations. However, all the samples had a similar grain size distribution with a maximum discrepancy of 17,7% in the fraction <2mm.
Assessment according to the European Landfill Directive (1999/31/EC) or the Austrian Landfill Directive 2008 excludes the slags from the classification "inert waste", due to higher Chrome contents in the solid mass (only required in the Austrian Landfill Directive 2008) and higher leaching test results for Flour and Sulphate. Generally, this study does not provide sufficient information for a classification as inert or hazardous.