Minimizing Chromium Leaching from Low-Alloy Electric Arc Furnace (EAF) Slag by Adjusting the Basicity and Cooling Rate to Control Brownmillerite Formation

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.