| Dry low-intensity magnetic separation has the advantages of simple processes,water saving,safe tailings storage,environmental protection,low investment,and low cost.It is widely used in the separation of strong magnetic minerals,especially suitable for the selection of iron ore in areas with water shortages,cold temperatures,and lack of tailings dams.However,the traditional dry magnetic separation adopts a vibrating feeder or conveyor belt for feeding,and due to the poor dispersion of ore particles in the air medium and the strong adhesion force,ore particles are prone to agglomeration and contain impurities,which affects the quality of the product.Especially for fine-grained minerals,the high surface energy of ore particles makes it easy for fine particles to stick together and form clusters with fine or coarse particles,resulting in poor separation selectivity.In serious cases,selectivity can even be lost,which limits the promotion and application of dry magnetic separation technology.This paper focuses on the problems of fine grained dry magnetic separation and researches the separation mechanism and equipment development of highintensity magnetic minerals in a gas flow dry low-intensity magnetic drum separator,which has important theoretical and practical significance in improving the selectivity of fine grained strong magnetic minerals in dry magnetic separation and promoting the level of dry magnetic separation technology in China.In order to solve the problem of low dispersion and poor selectivity in dry low-intensity magnetic drum magnetic separation of fine-grained strong magnetic minerals,air flow feeding for separation and the combination of numerical simulation and separation detection of multi-physics field coupling is proposed in this paper.Based on the dynamic characteristics of the pneumatic dry low intensity magnetic drum separation process,the paper analyzes the force situation of ore particles in the dispersion and separation stages,as well as the coupling relationship with multiple physical fields.COMSOL Multiphysics software is used to establish a multi-physics field coupling model for the magnetic separation process of dry drum air flow.A prediction system is constructed for the main factors affecting the pneumatic dry low intensity magnetic drum separation process and magnetic separation performance,including equipment structural parameters,operating parameters,process parameters,and ore particle properties.The multi-physics field coupling model is validated from three aspects: magnetic field distribution,flow field distribution,and separation indicators,and the accuracy of the model exceeds 90%.The validated multi-physics field coupling model is used to study the effects of various parameters on the dispersion and separation performance of ore particles in the pneumatic dry low-intensity magnetic drum separation process,including the type of air dispersion and feeding device,structural parameters,layout positions,separation chamber structure,magnetic pole separation characteristics,magnetic pole residual magnetism,air flow velocity,and drum speed.The structural research of the equipment shows that different air dispersion and feeding devices and separation chamber structures can significantly affect the dispersion of fine ore particles and the separation performance of the equipment.The use of a spiral fluidized dispersion feeding device in a "vertical upward" position can promote the dispersion of fine-grained ore particles and increase the effective length of the separation zone.The shape of the separation chamber can greatly change the flow characteristics of the pneumatic dry lowintensity magnetic drum separation process and the trajectory of ore particles,thus affecting the separation performance.The waveform structure of the separation chamber can strengthen the turbulent state of the air flow in the separation zone,enhance the collision of fine-grained ore particles on the outer wall of the separation chamber,and under the synergistic effects of gas disturbance and wall rebound,promote the dispersion of finegrained ore particles around the outer wall of the separation chamber and move towards the surface of the separation drum,producing a similar "secondary feeding" effect.This can improve the concentrate grade while enhancing the recovery of fine-grained high-intensity magnetic ore particles with high liberation degree particle dissociation.The study of magnetic pole separation characteristics shows that the pneumatic dry magnetic separation process is influenced by the shape of the separation chamber and the turbulent motion of the air flow.Each magnetic pole corresponds to different types,grades,and recovery of ore particles collected on the surface of the separation drum.There is a clear "zone difference separation" phenomenon of ore particles on the surface of the separation drum.Therefore,the size of each magnetic pole residual magnetism should be combined with the characteristics of the separation process and a "high-low-high-low-waveform" configuration should be used.From the recovery of various ore particles on the surface of the separation drum corresponding to the magnetic poles,the coarse-grained low-grade intergrowth ore particles and the fine-grained high-grade dissociation ore particles have equal recovery rates on the surface of the separation drum corresponding to the same magnetic pole,which causes the low-grade intergrowth ore particles to be layered and wrapped in the concentrate.Equal recovery and layered wrapped are important factors affecting the increase in concentrate grade.The use of graded separation can reduce the inclusion of low-grade intergrowth ore particles and increase the concentrate grade.Based on the theoretical research results,a new type of high-efficiency pneumatic dry low-intensity magnetic drum separator was proposed.The designed structure parameters of the magnetic separator were optimized using the established multi-physics field coupling model and the prediction system for the influence of magnetic separation process and magnetic separation performance.The new high-efficiency pneumatic dry low-intensity magnetic drum separator uses permanent magnet magnetic iron and has 12 magnetic poles arranged alternately in N-S poles,with a magnetic pole package angle of 308°.The residual magnetism of magnetic poles 1 to 12 is configured in a "high-low-high-low waveform" manner with values of 0.4 T,0.4 T,0.4 T,0.4 T,0.2 T,0.3 T,0.5 T,0.6 T,0.16 T,0.14 T,0.13 T,0.13 T.The separation chamber adopts a waveform structure,and the minimum distance between the waveform separation chamber and the drum surface is 40 mm,with a waveform amplitude of 15 mm.The pneumatic dispersion feeding device adopts a spiral fluidized type with an outlet width of 0.8 times the separation chamber spacing.Based on this design,a new ADMS-400 pneumatic dry low-intensity magnetic drum separator with a separation drum diameter of 400 mm and a length of 340 mm was developed.The ADMS-400 new type of pneumatic dry low intensity magnetic drum separator was used to dry-magnetically separate the magnetite ore with a TFe grade of 31.50% from Damenglong Iron Mine.With a grinding fineness of 80% at-0.074 mm,an air flow velocity of 4.5 m/s,a drum rotation speed of 30 r/min,and a feed rate of 0.3 kg/min,one roughing and one cleaning dry magnetic separation was carried out to obtain an iron concentrate with a yield of 33.94%,a Fe grade of 65.12%,and a recovery rate of 70.16%.The product indexes are similar to the results of low-intensity weak magnetic drum separation,indicating that the new type of pneumatic dry low-intensity magnetic drum separator has a good separation effect on fine-grained strong magnetic minerals and has a promising future for promotion and application.The multiphysics field coupling model and mechanism research of the pneumatic dry low-intensity magnetic drum separator established in this study has good reference value for dry magnetic separation theoretical research,equipment development,and separation tests. |
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