ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Regular Article
Mechanisms Involved in the Roasting of Pellets Composed of Stainless Steel Slag and Sodium Hydroxide to Extract Chromium
Yilong JiShaobo ShenJianhua LiuJinlei GuoYingshi Zhao
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2016 Volume 56 Issue 10 Pages 1751-1757

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Abstract

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 Ca3Mg(SiO4)2, Ca2SiO4, MgCr2O4 and MgO are the main phases from the SSL slag. Most of chromium from the slag was present in spinel phase (MgCr2O4). 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 MgCr2O4 were converted to Na3CrO4 at 500–700°C and CaCrO3 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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© 2016 by The Iron and Steel Institute of Japan
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