Physicochemical and mineralogical properties of stainless steel slags oriented to metal recovery

In the present paper, physicochemical and mineralogical properties of stainless steel slags oriented to metal recovery were studied by using various methods. The tests were conducted on two types of slag, namely EAF slag (Electric Arc Furnace) and AOD slag (Argon Oxygen Decarburisation). The samples were collected from the tailings of a slag processing plant operated by Bergslagens Stalservice AB in Sweden. Chemical analysis showed that the EAF and AOD samples contain 3.22% Cr and 0.075% Ni, and 1.71% Cr and 0.20% Ni respectively. Fe and Cr are mainly (about 70%) in the form of oxide while Ni is in the form of metal. Particle size analysis demonstrated that the EAF and AOD had been finely ground at the plant with 56 and 65% (-75 mum), respectively, containing a large amount of slime. According to X-ray Diffraction, Scanning Electron Microscope (SEM) and other studies, the main phases identified in EAF and AOD include Fe-Cr-Ni alloys, Fc-Cr oxides, Ca-Mg-Al silicates and Ca-Mg oxides (free CaO and periclase) with many mineral species. From SEM, Fe, Cr and Ni exist in the liberated alloy particles, association particles and complex particles. It is possible to recover the former two but the Fe-Cr-Ni in the latter one will not be easy to recover by mechanical separation. Some Cr also exists in the silicate phases and this Cr is impossible to recover by mechanical separation. However, Ni seldom exists in the silicate phases. Dissolution test showed that only a very small amount of EAF or AOD is dissolved in water, but in 1 M HCl solution, as high as 23.68% EAF and 31.04% AOD are dissolved, respectively. In addition, a phenomenon of particle size growth of the ground AOD was found and demonstrated by particle size analysis with a laser particle size analyzer and a Cyclosizer. Particle size growth of the ground EAF is not obvious, indicating that the hydraulic property of AOD is higher than EAR (C) 2003 Elsevier B.V. All rights reserved.