Stabilization of stainless steel slag via air granulation

Author(s): I. Nolet, L.L.C. So, J. Bolen, S. Mostaghel, J. Nell, Olle. Sundqvist, M.Mahdi, M. Lindvall, D. Metcalfe
This paper was published in Journal of Sustainable Metallurgy Vol.1, no.1- March 2015

Abstract

In stainless steel production, slag from argon oxygen decarburization (AOD) converters is dumped on to the ground and then slowly cooled. The slag undergoes phase transformation from β-dicalcium silicate (β-C2S) to γ-dicalcium silicate (γ-C2S) at approximately 500 °C to 450 °C, resulting in slag volume expansion, disintegration, and dust generation. The dusty slag leads to challenges in material handling, metals recovery, and emissions control. Some operations use slag additives to stabilize slag, but this solution is expensive and can limit the end use of slag due to inclusion of toxic elements. Air granulation was hypothesized as a water-free method for stabilizing AOD slag via rapid quenching. Pilot-scale experiments at Sandvik Materials Technology (SMT) with silicon-reduced AOD slags confirmed that air granulation can produce products which are stable and dust free. Mineralogical analyses further indicated that these air-granulated stainless slags contained either no or low content of γ-C2S and are therefore stable.