| Although Baotou Baiyunebo mine has created a large amount of rare earth tailings in the long-term development, there are still numerous iron and rare earth resources without effective utilization. Besides, the complexity of composition, vairty of element and disseminated structure cause a tremendous challenge of separation on valuable resources The article adopted magnetizing roast processing rare earth tailings. Iron was reriched into magnetic concentrate after magnetizing roast-magnetic separation, fluorite and rare earth resources were separated into tailings. Coal-based reduction and gas-based reduction were both adopted to the experiment, and transformation of main monominerals in the reducing roasting process which was investigated. Chemical analysis, XRD, SEM&EDS and TG-DSC were used to invesgigate the phase transition of roasting process and separation process of magnetic concentrate as well as tailings. It was a tentative exploration of comprehensive utlizition for Baotou rare earth tailings after iron ore dressing.The results of coal-based reduction and magnetic separation reveal:a concentrate containing iron grade with magntic concentrate of 45.22%, iron recovery of 74.89% was obtained on the optimized conditions of roasting temperature of 570℃, coal blending ratio at 2.2%, holding time of 40min, moulding pressure of 40MPa, and grinding finess of <74μm accounted 98.53%,<43μm accounted 92.35%. Under the condition of coal-based reduction bastnaesite is decomposed at 400～500℃, hematite is reduced at 500～600℃. When temperature is above 700℃, CaSiO3 is partly formed, and Fe2SiO4 which is detrimenal for magnetic separation. CaF2 is stable in 800℃. The reaction from hematite to magnetite processes rapidly in 570℃. The grain size grows with extend of holding time. When soaking time increases to 60min, solid solution of Si into the Fe3O4 occurs.The results of gas-based reduction and magnetic separation reveal:a concentrate containing iron grade of magnetic concentrate of 56.43%, iron recovery of 70.15% was obtained on the optimatized conditions of roasting temperature of 580℃, roasting time of 50min, CO concentration of 40%, CO-CO2 flow of 1.2L·min-1, grinding finess of <74μm accounted 98.20%,<43μm accounted 90.26% and magnetic field intensity of 235KA/m. Under the condition of gas-based reduction bastnaesite and hematite are not changed at 400℃. Bastnaesite decomposes rapidly accompanied with weak reduction of hematite. Fe2O3 is totally reduced into FesO4 in 570℃. In 605～640℃ some Fe3O4 is tansformed into FeO. Ca5(PO4)3F is stable in 675℃. More Fe3O4 is reduced into FeO in 675℃. CaF2 is stable in 400-675℃.Results of low intensity magnetic separation reveal:a large number of cracks occur in magntic concentrate, which help improving sponginess of minerals and promote the diffusion of reductant. Fluorite, quartz, pyrrhotite and minerals with calcium associated with iron minerals are entrained in iron concentrate. There are great disparties in the size distribution of tailings with numerous extremely fine particles. Rare earth mineral is enriched in tailings as the form of monomineral and paragenetic mineral associated with fluorite. Some minerals containing iron like aegirine, riebeckite and ankerite are separated into tailings.Results of monomineral experiment reveal:under the condition of CO atmosphere bastnaesite is not totally decomposed in 500℃. In 600℃ RECO3F->REOF accompanied with escape of CO2 and cracks. REOF is partly decomposed into (Nd, Pr)F3 in 675℃. REOF disappears in 800℃ accompanied with occurance of La2O3. CeO1.66 appears in 850℃ showing that Ce with +3 exists together with Ce4+. Some iron with +3 in aegirine is reduced to +2 in 570～650℃, but the magnetism hasn’t been changed much. In 570～650℃ the crystalline form is still as aegirine, and in 730℃ it’s transformed into Na-Fe-Si non-crystal body. High temperature reduction-magnetic separation experiment was carried out in 900～1300℃, concentrate containing iron grade of magnetic concentrate of 45.22%, iron recovery of 74.89% was obtained confirming the feasibility of utilization of iron in aegirine with high temperature reduction-magnetic separation. |
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