Phase transformation and structure evolution of chromite in the late stages of soda ash roasting process

Abstract

Soda ash (Na₂CO₃) roasting of the chromite is commonly used worldwide for the production of chromium compounds. However, chromium conversion yield of the chromite only reached 70–80% in industry owing to slow chromium conversion rate in the late stages of Na₂CO₃ roasting process, resulting in serious waste of resources. Through XRD, SEM, EDS, TG-DTA and HRTEM analysis, phase transformation and structure evolution of chromite in the late stages of Na₂CO₃ roasting of chromite were investigated. The results revealed that the chromite transformed from MgCrFe₂O₄ phase to the MgCr_0.4Fe_1.6O₄ main phase and Mg_1.5Na₉Si₁₂Al₁₂O₄₈ and NaSiAlO₄ minority phases first. The MgCr_0.4Fe_1.6O₄ phase gradually transformed to MgFe_1.8Cr_0.2O₄, MgFe_1.9Cr_0.1O₄ and MgFe₂O₄ phase. Microstructure, especially of the vacancies, was proved to play the key role in chromium conversion. Vacancies generated by thermal vibration needed greater activated energy, resulting in the low chromium conversion rate of chromite in the late stages of Na₂CO₃ roasting process.

Keywords

Chromite Phase transformation Structure evolution Vacancies Conversion rate Roasting

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