In order to extract the chromium from stainless steel (SSL) slag, the thermochemical processes involved in the roasting of pellets composed of SSL slag and sodium hydroxide were studied. It was found that Ca 3 Mg(SiO 4 ) 2 , Ca 2 SiO 4 , MgCr 2 O 4 and MgO are the main phases from the SSL slag. Most of chromium from the slag was present in spinel phase (MgCr 2 O 4 ). In addition, the chromium was also found in metallic phase (Fe-Cr) and periclase phase (MgO). These three Cr-containing phases were embedded in the silicate phases. During the pellet roasting, the silicate phases were destroyed by liquid NaOH and the low valence of insoluble chromium species such as MgCr 2 O 4 were converted to Na 3 CrO 4 at 500-700°C and CaCrO 3 at 800°C, respectively. Both were soluble in hot water. The residual chromium was only present in Cr-Fe-O phases. Many cavities were left on the pellet surface during the roasting, which facilitated the diffusion of both air and liquid NaOH. A high chromium extraction was achieved only when liquid NaOH had diffused into the cores of slag particles over 400°C.

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