In-situ observation and crystallization kinetics during the solidification of Cr-containing stainless steel slags

For a sustainable recycling process of Cr-containing stainless steel slags, high chromium recovery through selective crystallization could be achieved when thermophysical properties are controlled based on the crystallization kinetics. The in-situ observation and crystallization kinetics of synthesized Cr-containing slags has been studied. The crystallization characteristics in the CaO-SiO2-Al2O3-MgO-Cr2O3 slag system were investigated by using CLSM (confocal laser scanning microscopy) and DSC (differential scanning calorimetry). Analysis of crystallization kinetics was divided into spinel phase and calcium silicate phase. The growth mechanism of primary spinel phase has been demonstrated through CSD (crystal size distribution) theory with varying temperatures and cooling rates. The crystallization kinetic analysis of calcium silicate phase was performed using the modified Avrami equation and the combined Avrami and Ozawa equation. The Friedman differential isoconversional method was applied for determining the apparent activation energy during non-isothermal crystallization. Observations of crystalline phase morphologies and the precipitated phase was identified by using SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy) and XRD (X-ray diffraction) analyses. The change in the crystallization characteristics were compared with the slag melt structures analyzing by Raman spectroscopy.& COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Selective crystallization can achieve high chromium recovery for sustainable recycling of Cr-containing stainless steel slags by controlling thermophysical properties based on crystallization kinetics. In this study, in-situ observation and crystallization kinetics of synthesized Cr-containing slags were investigated using confocal laser scanning microscopy and differential scanning calorimetry. The crystallization characteristics of the CaO-SiO2-Al2O3-MgO-Cr2O3 slag system were analyzed, and the growth mechanism of primary spinel phase and crystallization kinetics of calcium silicate phase were demonstrated. The apparent activation energy during non-isothermal crystallization was determined using the Friedman differential isoconversional method.