| Dry magnetic separation is particularly advantageous in waterstressed areas due to its low production costs and low environmental effect.However,fine particle interaction is substantial in dry magnetic separation,decreasing magnetic separation efficiency.The research establishes an experimental platform for pneumatic flat and cylindrical dry magnetic separators,which employ a novel airflow divergence mechanism to improve fine particle dry magnetic separation processes.Using magnetic separation tests and computer simulation,basic and application research on airflow synergy enhancement of fine particle dry magnetic separation process were carried out systematically.The major research findings and conclusions are as follows:The optimum simulation designs for planar and sector magnetic systems were finished by optimizing magnetic field force homogeneity.The essential outlines of the airflow field in the separation zone were developed using simulations on porous saturated medium flow at various airflow velocities.Theoretical research of the 2D modeling of 3D magnetic separator’s composite physical field was carried out.Based on the simulation results,a dry pneumatic flat magnetic separator(DPFMS)and a dry pneumatic drum magnetic separator(DPDMS)were manufactured for experiments.Using an artificial mixed ore of magnetite and quartz as the feed,the influence of equipment separation angle on magnetic separation was investigated using the DPFMS and DPDMS test platforms,and it was found that airflow can significantly improve magnetic separation efficiency at 70 ° and 90 ° separation angles,but the auxiliary effect of airflow is exceedingly poor at 110° separation angle or above;The improvement effect of airflow on the separation efficiency of materials with varied particle sizes was explored.The smaller the particle size,the poorer the magnetic separation performance,and the greater the impact of airflow on separation;The influence of airflow velocity on magnetic separation was also investigated,and it was found that different particle sizes and magnetic field intensity require varied airflow velocities,or else the airflow will actually hinder magnetic separation.Actual ore magnetic separation tests were carried out using the DPDMS experimental platform.Because of the presence of weakly magnetic iron minerals and complex intergrowth in the raw ore,appropriate airflow velocity and cylinder speed can improve magnetic separation efficiency for coarser particle sizes(-0.150+0.074 mm,-0.074+0.038mm),but excessive airflow velocity can actually reduce magnetic separation efficiency;For-0.038 mm size fraction,the airflow significantly improves the magnetic separation efficiency.For micro fine particles,the magnetic field intensity on the cylinder surface,the airflow velocity on the cylinder surface,and the cylinder speed all have a considerable interaction on each other,and there is an ideal matching relationship among these three factors.The key advantages of DPDMS include: enhanced particle fluidization and improved the separation environment,increased the competitiveness between particles;extended the effective separation path length,enlarged the variances in separation routes for distinct particles.On the DPDMS experimental platform,a thorough research of particle force and motion behavior,as well as the reasonable matching of composite force fields,was carried out.The results showed that fluid drag force and centrifugal force are the core competitiveness of magnetic field force on the separation surface,and also are the key forces for regulating the capture of magnetic particles by the magnetic system.In the separation space,fluid drag force is only the key force for further regulating separation performance.The results showed that fluid drag force and centrifugal force are the fundamental factors for regulating the capture of magnetic particles by the magnetic system,as well as the core competitiveness of magnetic field force on the separation surface.Fluid drag force is merely one of several forces that may be used to further regulate separation performance in the separation space.Comparing with the magnetic force,gravity force and inertial force,fluid drag force becomes more significant as particle size decreases.Comparing with the magnetic force,gravity force and inertial force,fluid drag force becomes more significant as particle size decreases.Except for gravity force,a reasonable match of magnetic field force,fluid drag force,and centrifugal force is essential for regulating magnetic separation efficiency.The appropriate fluid drag force and centrifugal force on particles can result in greater motion trajectory difference between various particles under specified magnetic field intensity.Different particle sizes need different suitable airflow velocities.The smaller the particle size,the narrower the acceptable airflow velocity ranges.A plate microscopic analysis model and a realistic cylinder separation model were built for the analysis of dense particle groups in magnetic separation process.The plate microscopic analysis model focuses on the effectiveness of contact and magnetic models,as well as the basic motion behavior of particle groups.The results reveal that magnetite particles in a magnetic field may quickly create a magnetic chain and move towards a strong magnetic area,but the magnetic chain structure varies depending on the conditions.The magnetic chain created by 10μm particles largely collapsed under the action of van der Waals force;while 100μm particles form a more "coarse and short" multi chain structure,with no influence of van der Waals force on the magnetic chain structure.The movement behavior of different magnetite intergrowth is similar to that of magnetite monomer,but the magnetic chain structure is rather irregular,which aggravates particle inclusion.The use of air flow causes single quartz and hematite particles to be blown away from the magnetic chain,and the 10μm particles are more affected by airflow.The cylindrical separation model focuses on the change of magnetic chain structure of particle groups and the separation performance of equipment in the separation process.The results revealed that using a 1m/s airflow enhanced the concentrate grade considerably for three categories of raw materials: 100μm artificial mixed ore,simple intergrowth,and complex intergrowth.The concentrate grade was also enhanced by applying a 0.2m/s airflow to the 23μm particle simple intergrowth.When the selected raw materials contain intergrowth or fine particles,the strengthening impact of airflow on the effectiveness of dry magnetic separation is quite substantial.133 figures,30 tables and 173 references... |
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