| As the first large rare earth deposit discovered and developed in China,Baotou mixed rare earth deposit has the world's largest reserves of rare earths.Since the 1980s,the industrial flotation practice by using hydroximic acid as the special collector of rare earth minerals indicated that the flotation technology of mixed rare earth minerals has been mastered.Nowadays,the mineral resources with characteristics of low target mineral content,fine particle size,complex mineral species and difficulty in mineral separation have dominated primary domestic resources,but the processing technology of the mixed rare earth ore failed to achieve continuous improvement.Especially since 2015,the plant of Baogang Group implemented the comprehensive utilization projects of mineral processing,causing feed particle size of mixed rare earth ore in flotation refined and the composition of ore pulp increasingly complex,which made it difficult to improve the index of mineral processing because of the function of the addition and compounding of the conventional agents in hydroximic acid system hard to work.At the same time,China has been paying more and more attention to environmental protection.In order to solve the problem of environmental pollution,the rare earth metallurgy process put forward higher requirements on concentrate grade,but the improvement of concentrate grade will inevitably lead to the reduction of ore processing recovery.In view of these problems,this paper systematically studied the mineral particle properties of mixed rare earth minerals,proposing a flotation method that could adapt to the current complex slurry system and designing a flotation of component velocity process based on the nonlinear floatability of rare earth minerals to obtain a good index in the industrial test.The main results are as follows:The crystal structure and lattice plane orientation of the bastnaesite were studied.The results showed that the rare earth atoms in the bastnaesite were replaced by calcium atoms in the same image,which made the crystal structure preferentially orient along the crystal planes(110)and(300)and the floatability of the mineral also increased.The characteristics of cleavage and dissemination of particle size in different types of ores were investigated and it was found that the mixed rare earth minerals had the characteristics of uneven grain size and incomplete cleavage surface.The enrichment regularities of the rare earth mineral particle sizes,shapes and pore surfaces in the flotation process were comprehensive studied.According to the regularities,it was also found the best flotation conditions of rare earth mineral particle size distributed among 20?30 ?m.Moreover,the particles had a faster flotation rate,whose three-dimensional structure were closed to the circular and diameter of uneven surface channel were mainly distributed among 40?200 nm with closed at one end of pore.The kinetics of particle-bubble interaction showed that increasing slurry concentration was an effective method to solve the problem of large loss of coarse and fine rare earth minerals in the process of selecting mixed rare earth ore.The interaction between particles and bubbles showed that the bridging function of the interfacial nano-bubble formed on the surface pores of rare earth minerals could significantly increase the attractive interaction distance between particles and bubbles by triple.The influence of flotation temperatures on flotation index and its mechanism were studied.The flotation test results showed that the grade and recovery rate of flotation concentrate increased with the increase of temperatures.According to the analysis of Zeta potential,FTIR and XPS,it was concluded that the surface adsorption stability between hydroximic acid and rare earth minerals increased with the increase of temperature,and the adsorption stability of bastnaesite was greater than that of monazite.Influence of unavoidable ions in pulp on index of flotation was studied.Flotation test results showed that calcium and magnesium ions of rare earth minerals deteriorated flotation indexes.FTIR and 29 Si MAS NMR mechanism analysis showed that the calcium and magnesium ions reacted with sodium silicate to form amorphous gel,and the degree of polymerization of C-S-H gel increased with the increasing temperatures.However,the degree of polymerization of C-S-H decreased with the extension of time.When the of calcium and magnesium ions coexisted,the style of gel C-S-H changed into M-S-H with the increasing temperatures,but the style of gel C-S-H would convert into M-S-H with the increasing time.The formed amorphous gel would adhere to the surface of rare-earth mineral and gangue minerals,which reduced the index of flotation.Moreover,sulfate could promote the flotation of rare earth minerals to some extent.The main reason was that sulfate could selectively adsorb on the surface of calcite and fluorite,while the adsorption amount of bastnaesite and monazite was less by XPS analysis.The feasibility and the mechanism of advanced oxidation process(APOs)collaborated with hydroximic acid in the flotation of rare earth minerals were studied.'The flotation test results showed that APOs could make the recovery of rare earth concentrate grade will be increased by 5%under the same recovery conditions.Compared with H2O2,US and US/H2O2 schemes,US/H2O2 showed better performance.Theoretical analysis showed that APOs could oxidated Ce(?)of rare earth minerals surface for Ce(?)to accelerate chelate reaction with hydroximic acid.At the same time,the degradation efficiency of total organic carbon(TOC)in mineral processing backwater by APOs was studied.The unavoidably ions in ore pulp could inhibit the degradation.Rare earth minerals and fluorite could contribute to degradation,while calcite and mixed tailings would inhibit it.At the same time,it was also found that by optimizing the reaction conditions,the degradation rate of 70%could be achieved in about 15min,which meant that this scheme could be completed in the flotation process without separate treatment.The sedimentation experiments of CO2 slime were carried out and it was found that the complete sedimentation of slime in pulp could be basically achieved after passing in quantitative CO2 for 30 min.The contents of calcium,magnesium and silicon in the pulp before and after sedimentation under different pH conditions were investigated,and it was also found that the penetration of CO2 could significantly reduce the contents of calcium and silicon in the pulp.Moreover,the sedimentation rate increased with the increasing of pH value.The actual ore processing backwater in experiments were fully verified,and FTIR analysis found that the generated products contained calcium carbonate.The reaction mechanism of this process was that CO2 could react with C-S-H calcium ions with low degree of polymerization to form calcium carbonate precipitation,and the decrease of pH value made the residual silicate root in the pulp sowed a strong flocculation.Establishment of fractal-like flotation kinetics model was obtained and the flotation process under different conditions could be described by this model.The fractal dimension ds could reflect the limitation of flotation rate with time.A constant selectivity index model based on constant flotation time and a nonlinear model of selectivity index changing with time and ore grade are presented.According to the theory,it is necessary to adopt fractional flotation to achieve high grade and recovery rate.According to these results,the industrial test and laboratory-scale machine-column combined Flotation process of component velocity were designed and carried out to improve the grade of rare earth concentrate from 50%to 65%and the high recovery rate. |
PDF Full Text Request