The stabilization of chromium is of great importance to the use of stainless steel slag (SSS), and the influence of lime on the stability of chromium is currently unclear. In this work, the variation of phase transformation and chromium distribution with slag basicity (CaO/SiO2) were investigated experimentally, and the leaching ability of chromium was evaluated. Results showed that chromium-bearing phases were glass, dicalcium silicate (C2S), spinel, and periclase, while the degree of enrichment of chromium in these phases was found to be closely related to the basicity. The optimal basicity obtained in this research was 1.5, with the chromium mainly present in the stable spinel and exhibiting the lowest leaching ability. The product layer structure of unmelted lime was studied as well, showing a periclase layer and a Ca2SiO4 layer. Some CaCr2O4 had formed in the periclase layer, which is potentially hazardous for the environment and living organisms.
The chromium elution behavior of stainless steel (SS) slag depends highly on the chromium distribution, and the molten modification process proved to effectively improve the chromium enrichment in stable phases. However, the phase transformation and variation of chromium stability during the subsequent cooling process is still poorly understood. In this work, the phase composition and chromium distribution of SS slag from different quenching temperatures were experimentally studied, and the stability of chromium-bearing phases was evaluated using standard leaching tests. The results indicated that dicalcium silicate and spinel phases had formed in the molten slag at 1600 °C, while the dicalcium silicate disappeared and the phases of merwinite and melilite precipitated when the temperature decreased from 1600 to 1300 °C (at a rate of 5 °C/min). During this cooling process, the chromium migrated from other phases into the spinel, significantly suppressing the chromium elution. The leaching results also demonstrated that the potential chromium-bearing phases of glass, dicalcium silicate and merwinite are unstable and are presumably the main source of chromium release. The treated SS slag meets the requirements for the utilization of chromium-bearing slag in the cement and brick industries.
The low-reactive tundish flux is urgently required for the smelting of rare-earth steels. The effect of Ce 2 O 3 content on the properties (melting point and viscosity) and structure of CaO-Al 2 O 3 -Ce 2 O 3 -MgO-SiO 2 slag were analyzed in the present investigation. The research results indicated that the polymerized Q Al 4 and Q Al 3 units were modified to Q Al 2 units in aluminate, and the depolymerization of SiO 4 -tetrahedrons from Q Si 1 to Q Si 0 units with Ce 2 O 3 addition increasing from 5 wt% to 20 wt%. In addition, when the Ce 2 O 3 addition increased from 15 wt% to 20 wt%, the increasing area fraction in AlO 6 -octahedral units further led to a decrease in the degree of polymerization (DOP) in the melts. When the Ce 2 O 3 addition increased from 5 wt% to 20 wt%, the melting temperature decreased from 1 320°C to 1 301°C. Additionally, the softening temperature and the fluidity temperature also decreased 20°C and 24°C, respectively. The viscosity decreased as the Ce 2 O 3 addition increased from 5 wt% to 20 wt%, which was attributed to the decreased DOP and the increased superheat. A reasonable content for Ce 2 O 3 should not be excess 10 wt% in the current slag.
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