Analysis of Cr with Various Valence States in Industrial EAF Slag for Making Stainless Steel

摘要

Slags of stainless steel making by EAF process in one plant from south and the other from north China were selected. The qualitative and quantitative analysis of all elements in samples were investigated first, the possible phases were identified by diffraction. Micro-morphology and composition analysis showed that Cr exist in iron-based alloy, chromite phase and Cr-containing silicate phase. It inferred that Cr (0) would be in iron-based alloy drops, Cr (Ⅲ) would be in chromite phase. The Cr valence states in slag were assumed as 0, +2, +3 and +6. The caustic plus carbonate sodium solution was adopted to leach Cr(Ⅵ) as CrO_4~(2-); oxalic acid was applied to leach the Cr(0) in alloy drops; FeCI_3-HCI-NH_4CI combined with V~(2+)-HCI leaching process, the Cr(Ⅱ) in slag would change to Cr~(2+) in solution; the resident containing Cr(Ⅲ) was smelting by Na_2O_2. Cr in different valence states were separated and detected. The optimized leaching processes of Cr (Ⅵ) and Cr (0) were investigated. The influence of the leaching process on existence of other phase was checked also. The analysis results showed the route of separation and analysis is suitable for the slag samples. Both slag samples were with the same trend of contents in various Cr states. Among the states, Cr (0) content is highest, about 2.0-4.5 mass%; the second highest content is Cr (Ⅲ), about 1.4-2.7 mass%; the content of toxic Cr (Ⅵ) is about 80-310 ppm, the lest one is Cr (Ⅱ), about 1.0-2.1 ppm. This study would provide an experimental method and basis for the utilization and environmental impact of stainless steel smelting slag.