Characteristics of Bauxite Residue–Limestone Pellets as Feedstock for Fe and Al2O3 Recovery

Abstract

Experimental research was carried out to produce pellets from bauxite residue for the further extraction of iron and alumina. Bauxite residue and limestone with three different mixture compositions were pelletized experimentally via agglomeration followed by drying and sintering at elevated temperatures. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the phase and microstructural analysis, respectively. Tumble, abrasion, and breaking load tests were applied to determine the strength of the pellets. For measurement of porosity and surface area, mercury porosimetry and BET surface area methods were applied. It was found that at 1100 °C sintering temperature, all the three sintered pellet compositions have a moderate porosity and low strength, but the reverse result was found when 1200 °C sintering temperature was applied. Moreover, for the pellets sintered at 1150 °C high strength and proper porosities were obtained. In the sintered pellets, iron present in form of brownmillerite (Ca2Fe1.63Al0.36O5), srebrodolskite (Ca2Fe2O5), and fayalite (Fe2SiO4), while alumina present mostly in gehlenite (Ca2Al2SiO7) and little fraction in mayenite (Ca12Al14O33) and brownmillerite phases. The identified phases are the same for of the three pellets, however, with variations in their quantities. Porosity and mechanical properties of pellets are inversely related with both varying sintering temperature and composition. It was found that with more CaCO3 use in pelletizing, higher porosity is obtained. However, with increasing sintering temperature the strength of the pellets increases due to clustering of particles, while porosity decreases.