An Investigation on Reduction of Calcium Added Bauxite Residue Pellets by Hydrogen and Iron Recovery through Physical Separation Methods

Abstract

This study investigates the properties of H2-reduced calcium-added bauxite residue, self-hardened pellets, and the feasibility of iron recovery through electrostatic and magnetic separation methods. The oxide pellets are prepared via a mixing of bauxite residue, calcite, and quicklime. The self-hardened pellets are reduced at 1000 °C with hydrogen gas flow for 120 min. The chemical composition, phase identification, and microstructural observations are executed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. The porosity and strength of the self-hardened pellets are performed by the Mercury intrusion porosimetry and tumbling tests, respectively. The separation of iron is examined through a dry electrostatic technique, and in wet conditions, i.e., via Davis Tube and low-intensity magnetic separation (WLIMS). The effect of the magnetic field (0.1, 0.25, and 0.32 T) is tested on two different particle size fractions (−212 + 106 µm and −106 + 74 µm). It is found that most of the iron oxide in the bauxite residue is converted to metallic iron, which corresponds well with both XRD and SEM results. The Carpco electrostatic tests indicate that this approach is inefficient for the studied type of material because of the intensive association of iron with the rest of the components leading to transferring it to the middling rather than to conductive product. However, both the Davis Tube and WLIMS approve a reasonable improvement in the Fe content from 22% to 37% with acceptable recoveries. The results of the Davis Tube show that there is an optimum magnetic field and particle size for maximization of Fe grade and recovery. Finally, further suggestions are highlighted for the physical beneficiation of studied bauxite residue with the purpose of maximizing iron grade and recovery.

Water and Alkali Leaching for Simultaneous Iron and Alumina Separation from Hydrogen-Reduced Bauxite Residue-Calcite Pellets

“…BR, limestone, and quicklime were mixed in 65.4, 25.7, and 9.3 wt.%, respectively, in a tubular mixture. BR and calcium (CaCO 3 and CaO) were mixed in such a ratio so that it would form CaO.Al 2 O 3 , 2CaO.SiO 2 , and CaO.TiO 2 during the heat treatment process, which has been described in previous results [12]. In making self-hardened pellets a fraction of CaCO 3 , is replaced with fine CaO to making use of the cementing nature of CaO, which gives strength to the pellets in the pelletization process and in the further aging process.…”

“…From our previous work, during iron recovery by dry magnetic separation, there was less enrichment of the iron percentage in the separated magnetic fraction [12]. The low enrichment of iron in the magnetic fraction is due to the encapsulated matrix of iron and alumina, which results in both the presence of iron and alumina in the magnetic fraction.…”

“…In both the applied processes, calcium oxide is higher in the nonmagnetic fractions than in the magnetic portions. The iron present in reduced pellets was around 22 wt.% [12]; after magnetic alkali leaching, it increased to 43.5 wt.%, while, in the case of water leaching, the Fe content of the magnetic portion increased to 35.3 wt.%.…”

“…After self-hardening, these pellets were dried in an oven to remove free moisture, then reduced in a vertical tube furnace by purging hydrogen gas from the bottom of the furnace. The schematic view and the furnace description are presented elsewhere [12].…”

An Invitation on Characterization of H2-Reduced Bauxite Residue and Recovering Iron through Wet Magnetic Separation Processes

“…Enhancin grade is most likely attributed to the increase in the liberation degree of iron-bea phases, while the reduction in Fe recovery is caused by the attenuation of particle siz this regard, Shao et al [26] reported a similar trend of reducing hematite recovery decreasing particle size. Most recently, Hassanzadeh et al [27] investigated the effe magnetic field and particle size on an H2-reduced calcium-added bauxite residue. T found that coarsening the particle size from −106 + 74 µm to −212 + 106 µm at a cons magnetic gradient of 0.1 T diminished the Fe grade from 35% to 25% with an increas iron recovery from 40% to 83%.…”