Abstract
A novel approach for recovery of iron and rare earth elements (REEs) from Bayan Obo tailings of Baotou, China, was developed by combining magnetizing roasting, magnetic separation, (NH4)2SO4 activation roasting, and water leaching. Thermodynamic analysis of carbothermal reduction was conducted to determine the temperature of magnetizing roasting, and it agreed well with the experimental results. The maximum recovery of Fe reached 77.8% at 600 °C, and the grade of total Fe in the magnetic concentrate was 56.3 wt. %. An innovative approach, using water to leach REEs after (NH4)2SO4 activation roasting, was used to extract REEs from magnetic separation tailings. The main influence factors of the leaching recovery during (NH4)2SO4 activation roasting, were investigated with the mass ratio of (NH4)2SO4 to magnetic separation tailings, roasting temperature and roasting time. The leaching recoveries of La, Ce and Nd reached 83.12%, 76.64% and 77.35%, respectively, under the optimized conditions: a mass ratio of 6:1, a roasting temperature of 400 °C and a roasting time of 80 min. Furthermore, the phase composition and reaction process during the (NH4)2SO4 activation roasting were analyzed with X-ray diffraction (XRD), energy dispersive X-ray spectroscopy & scanning electron microscopy (EDS-SEM) and thermogravimetry & differential scanning calorimetry (TG-DSC), and the leaching solution and leaching residue were also characterized.
Highlights
The Bayan Obo ore deposit located in Inner Mongolia of China is one of the world’s largest iron-rare earth mines, the symbiosis of rare earth elements (REEs), iron, niobium, thorium scandium, fluorine, phosphorus, and other 71 elements [1]
It is notable that the RECO3 F and REPO4 in the Bayan Obo tailings were decomposed into rare earth oxides during the process of magnetizing roasting, which was beneficial for further leaching recovery of REEs
The total Fe content of the magnetic separation concentrate was determined by the potassium dichromate volumetric method, and the REEs content of the magnetic separation tailings was determined by inductively coupled plasma optical emission spectrometry (ICP-OES)
Summary
The Bayan Obo ore deposit located in Inner Mongolia of China is one of the world’s largest iron-rare earth mines, the symbiosis of rare earth elements (REEs), iron, niobium, thorium scandium, fluorine, phosphorus, and other 71 elements [1]. Metals 2017, 7, 195 from 6.8% to 8.85%, which is almost close to, or even slightly higher than the grade of raw ore, due to the low recovery of REEs [7] Recycling of such a large amount of rare earth resources is beneficial to environmental improvement, and is worth considerable economic value. It is notable that the RECO3 F and REPO4 in the Bayan Obo tailings were decomposed into rare earth oxides during the process of magnetizing roasting, which was beneficial for further leaching recovery of REEs. The dissolution of rare earth oxides was significantly strengthened in the process of (NH4 ) SO4 activation roasting—La, Ce, Nd and other metallic element were converted into corresponding sulfates [13]. It was hoped that a novel technological process and theoretical basis for recycling REEs and iron from the Bayan Obo tailings could be developed
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