Abstract
Brownmillerite is connected to chromium leaching when present in steel slags. To prevent chromium leaching, brownmillerite in slag should be prevented. Two methods for decreasing brownmillerite content in low-alloy electric arc furnace (EAF) slag were investigated: decreasing the basicity and increasing the cooling rate. The methods were tried on both laboratory scale and in full-scale production. In the laboratory scale experiments, chromium leaching decreased as the basicity decreased until brownmillerite was no longer present, slower cooling resulted in increased chromium leaching, and faster cooling decreased chromium leaching. In full-scale production, basicity modified single batches, with a basicity below 2.2, generally leached less chromium than slag batches with higher basicity, thus verifying the correlation between basicity and chromium leaching seen in laboratory scale experiments. The cooling process in the full-scale experiments was achieved either by letting the slag cool by itself in the air or by water spraying. The water-sprayed slag, which cooled faster, had less chromium leaching than the air-cooled slag. The full-scale production experiments confirmed that both decreasing basicity below 2.2 and increasing the rate of cooling could be used to decrease chromium leaching.
Highlights
IntroductionThe steel production of Sweden almost reached 4.7 million tonnes of crude steel in 2017; at the same time, around 1.3 million tonnes of slag was produced [1]
Slag is produced as a by-product of pyrometallurgical metal production
The European Council Directive (2003/3/EC) limits chromium leaching to 0.5 mg/kg for the material to be classified as inert landfill material
Summary
The steel production of Sweden almost reached 4.7 million tonnes of crude steel in 2017; at the same time, around 1.3 million tonnes of slag was produced [1]. The properties of slag make it superior to natural resources, for example the porosity of slag in asphalt reduces road noise [2,3]. Natural virgin resources can be preserved and unnecessary landfill is prevented. Different types of slag consist of different minerals, which make slag a versatile material. Some of these properties, such as volume expansion [4], disintegration [5], and leaching of some elements, restrict how slag can be used.
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