The Stabilization Efficiency and Mechanism towards Chromium Residue by Microwave and FeSO4 Treatment
The"returning to yellow"phenomenon usually occurs in treated chromium residue,which is related to the rere-lease of Cr(Ⅵ)in undissolved Cr(Ⅵ)-bearing minerals.In this regard,the complete dissolution of unstable Cr(Ⅵ)-bearing minerals and the release of Cr(Ⅵ)are crucial to the long-term stability of chromium residue.In this study,the dissolution of ettringite was facilitated by microwave(MW),and then the efficient stabilization of chromium residue was achieved via MW combined with FeSO4 treatment.In general,the apparent activation energy of ettringite dissolution(35.8 kJ/mol)was signifi-cantly reduced by MW irradiation,and hence promoting the rapid dissolution of ettringite to release Cr(Ⅵ).Furthermore,the dissolution of hydrotalcite was promoted by H2SO4 from FeSO4 hydrolysis in MW field,leading to the complete dissolution of Cr(Ⅵ)-bearing minerals in chromium residue.Moreover,the reduction efficiency of Cr(Ⅵ)by FeSO4 was significantly im-proved by MW,which reached up to 100％with the treatment of MW(462 W)combined with low dose FeSO4(w=21.5％).More importantly,the formation of crystalline Cr(Ⅲ)-bearing minerals,including FeO·Cr2O3 and Cr2O3 were promoted by MW irradiation.There was no"returning to yellow"phenomenon occurred after one year.The stabilization and safe disposal of chromium residue was obtained.Therefore,this study provided data support and theoretical basis for the application of MW-coupled FeSO4 treatment in the field of chromium residue stabilization.
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