Investigation on the fluidized attrition characteristics of red mud oxygen carrier and its iron enrichment via chemical looping fluidization process

Abstract

The loss of oxygen carriers caused by fluidized attrition is inevitable and non-negligible in the chemical looping process. Using low-cost solid waste as oxygen carriers, such as red mud with satisfactory reactivity, is a compromise strategy to reduce the operational makeup cost. In this work, the fluidized attrition characteristics of red mud oxygen carrier was innovatively and convincingly investigated in a standardized reactive attrition device based on the jetting fluidized bed. The real-time attrition curves and particle size distribution of red mud under non-reactive (cold, hot) and thermochemical reactive conditions revealed higher attrition resistance of Fe-based material at elevated temperatures without thermochemical reactions. More significant attrition was observed under the thermochemical reduction stage. The initial abrasion and subsequent fragmentation caused newly formed sub-particles subjected to “secondary abrasion”, further producing elutriated fines. The profile EDS results demonstrated iron migration and enrichment in the local external surface and internal pores influenced by the Kirkendall effect. Unlike other studies conducted in the bubbling bed, no continuous and obvious iron enrichment layers appeared in the edge areas of the most rounded particles’ profile using the jetting fluidized bed. The observed phenomenon implied that the abrasion-derived recovery rate matched well with the solid-phase (Fe) migration rate, thereby effectively achieving a higher iron enrichment rate in fines (58% higher than the raw material) via shorter operations. Moreover, this work provides a new idea for upgrading abundant low-iron solid waste into readily usable iron-rich materials for ironmaking via chemical looping fluidization process.