Solidification and recovery of Cr from hazardous Cr-bearing steel slag: Selective solidification, super-gravity separation and crystal characterization
Yu Li, Jintao Gao, Xi Lan, Guoliang Feng, Yanling Zhang, Zhancheng Guo
Abstract
Massive hazardous Cr-bearing steel slag is produced from the electric furnace smelting process of stainless steel, while the soluble poisonous hexavalent chromium (Cr(VI)) seriously limits the sustainable utilization of the slag. In this study, a novel method of selective solidification and super-gravity separation was proposed to recover Cr resources from Cr-bearing steel slag safely and efficiently. Firstly, Cr elements were selectively solidified into Cr-spinel in Cr-bearing steel slag with wt.%(MgO) = 6.00, and the high-purity Cr-spinel crystals ((Mg 0.43 Fe 0.28 Mn 0.29 )(Cr 1.67 Al 0.33 )O 4 ) were effectively recovered from the molten slag via super-gravity separation with a significant Cr 2 O 3 content of 58.08 wt% and a high Cr recovery rate of 88.58 %. On this basis, the chemical formulas and crystal structures of various high-purity Cr-spinel crystals were characterized and the solidification mechanism of Cr in Cr-spinel was determined, to verify that Cr 3+ was accordingly substituted by Al 3+ when Fe 2+ and Mn 2+ were substituted by Mg 2+ , and Cr elements were efficiently solidified and recovered into the Cr-spinel in stable trivalent chromium (Cr(III)) based on the XPS results. Thus the effective leaching amount of Cr in Cr-spinel was as low as 0.011 mg/L, which provided a basis for sustainable utilization of Cr-bearing steel slag.