| Bayan Obo ore is a rare and polymetallic Fe-RE-Nb deposit in the world.Many complicated factors such as complex elements and mineral composition,low grade,fine-grained dissemination and numerous kinds of minerals make it difficult to separate and extract the resources.At present,the technology of weakly magnetic separation-strong magnetic separation-flotation is the main technology in the Bayan Obo ore dressing.However,large amounts of resources have been discarded during the processing of Bayan Obo ore,resulting in a low utilization ration of valuable elements.Therefore,the research and development of the new technology of Bayan Obo resource is very important to our rare earth industry.In this thesis,the Bayan Obo weakly magnetic tailings were investigated as raw materials.A new technology of recovery Fe,RE,F and P from Bayan Obo weakly magnetic tailings was designed.The technology conditions and reaction mechanism of the new technology were studied.The process mineralogy on Bayan Obo weakly magnetic tailings was studied using X-ray diffraction analysis,scanning electron microscope,mineral liberation analyzer,laser particle analyzer and electron probe microanalysis.The results indicated that the particle size of Bayan Obo weakly magnetic tailings was fine and particles of<75 ?m accounted for more than 90.75%.In the main recoverable resources,the hematite and gathered in particles of>10?m,and about 98.61%of the bastnaesite,95.62%of the monazite and 99.92%of the fluorite were concentrated in particles of>10 ?m.The valuable elements were very low-grade in Bayan Obo weakly magnetic tailings.The contents of Fe,REO,F and P2O5 were 14.38%,9.60%,12.57%and 3.53%,respectively.Iron mainly occurred in the form of hematite.Rare earth elements mainly occurred in bastnaesite and monazite.Fluorine mainly occurred in fluorite and bastnaesite and phosphorus mainly occurred in apatite and monazite.There were amounts of gangue minerals,such as beloeilite,osannite,quartz,barite,dolomite and mica,etc.According to the analysis of process mineralogical characteristics of tailings,a beneficiation-metallurgy combination process of "gravity separation-flotation-one step roasting-low intensity magnetic separation-hydrochloric acid leaching" was proposed.The results of gravity separation showed that 97.77%of REO and 93.39%of Fe were concentrated in gravity concentrate,and 77.21%of F and 59.99%of P2O5 were concentrated in gravity tailings.The closed-circuit experiment of flotation fluorite of single-stage roughing and two-stage concentrating was carried out,and the flotation concentrate containing 81.86%of CaF2 with the CaF2 operation recovery of 92.68%was obtained.The apatite concentrate containing 54.38%of Ca5(PO4)3F with the Ca5(PO4)3F operation recovery of 93.61%was obtained by the closed-circuit experiment of flotation apatite of single-stage roughing,single-stage concentrating and single-stage scavenging.Simultaneous measurements of thermogravimetry and differential thermal analyses and X-ray diffraction analysis were applied to investigate the thermal decomposition reactions and thermodynamics.The results showed that hematite was reduced into magnetite and rare earth minerals were decomposed into rare earth oxides at 650 ?.Through signal factor experiments,the optimum processing conditions of one-step roasting were obtained(i.e.,roasting temperature,650 0C;roasting time,60 min;coal content,4.0%;Ca(OH)2 dosage,6.0%;and NaOH dosage,2.0%.).The leaching ratio of rare earths could reach 93.14%and the reduction rate of hematite reached 2.31 under the optimal conditions.Magnetic separation test was made on separating iron from the roasted samples by a process of stage grinding,one roughing(200 mT)and one cleaning(100 mT).After that,the magnetic concentrate containing 72.35%of total Fe with the Fe recovery of 86.28%and magnetic tailings containing 24.30%of REO with the REO recovery of 98.85%were obtained.The reaction mechanisms of the decomposition of bastnaesite and monazite and the reduction of hematite were investigated by scanning electron microscope and X-ray diffraction analysis.Hematite was reduced to magnetite along the chemical reaction sequence of Fe2o3->Fe3o4 and the spatial sequence from the outer layer within the particle to its inner core.Bastnaesite was decomposed along the chemical reaction sequence of REFCO3->REOF+REO+CaF2?REO+CaF2 and the spatial sequence from the outer and secondary outer layer in the particle to the inner core.Monazite was decomposed along the chemical reaction sequence of REPO4?Ca3(PO4)2+REO?REO+Ca5(PO4)3F and the spatial sequence from the outer layer within the particle to its inner core.The reaction kinetics of the reduction of hematite and the decomposition of bastnaesite and monazite were investigated by the unreacted shrinking core model.The reduction of hematite and the decomposition of rare earth minerals could be described by the unreacted shrinking core model at 650 ?.The reaction rate of reduction of hematite was controlled by chemical reaction control mode and the apparent activation energy was 48.22 kJ·mol-1.The reaction rate of decomposition of rare earth minerals was controlled by the diffusion of reaction adjuvants through the solid product layer and the apparent activation energy was 13.80 kJ·mol-1.The technology parameters of the weakly magnetic tailings leached by hydrochloric acid-citric acid and the leaching liquid basified by sodium hydroxide were studied.By single factor experiment,the optimum conditions of dephosphorization were as follows:HCl concentration was 0.50 mol·L-1,citric acid concentration was 0.05 mol·L-1,leaching temperature was 40 ?,liquid to solid was 10:1,stirring speed was 200 r·min-1 and leaching time was 50 min.In the optimization of process conditions,the phosphorus leaching ratio was reached 97.36%.On the conditions of pH value of 9.5,temperature of 20 ? and time of 30 min,the operation recovery ratio of phosphorus from pickle liquor was 98.55%.Furthermore,the technology parameters of leaching residue of phosphorus by HC1 to dissolve REO were studied.The leaching ratio of REO was up to 97.42%under the optimum technology conditions of leaching temperature of 50 ?,HCl concentration of 3.50 mol·L-1,leaching time of 70 min,liquid to solid of 10:1 and stirring speed of 200 r·min-1.The distribution of valuable elements of Bayan Obo weakly magnetic tailings in beneficiation-metallurgy combination process was investigated.The results slowed that the overall recovery ratio of iron,rare earth,fluorine and phosphorus is 80.57%,91.04%,71.59%and 91.83%,respectively.At the same time,the niobium,scandium and thorium were traced during the full flow.It was found that 79.63%of Nb2O5,50.48%of SC2O3 and 81.44%of ThO2 were concentrated in the leaching residue of rare earth.The beneficiation-metallurgy combination process not only recycled the iron,rare earth,fluorine and phosphorus,but also made the niobium,scandium and thorium concentrate into the leaching residue of rare earth,which could be used for recycling the niobium,scandium and thorium.In conclusion,the new technology of comprehensive recovery of iron,rare earth,fluorine and phosphorus from Bayan Obo weakly magnetic tailings satisfied the comprehensive utilization of Bayan Obo resources.The new technology will provide much support to comprehensive utilization of Bayan Obo resource. |
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