Fundamental Research On The Particle Capture And Accumulation Around Upstream And Downstream Side Of Matrix In High Gradient Magnetic Separation

High gradient magnetic separation（HGMS）is an important method of recycling weakly magnetic minerals.A deep insight onto the fundamental theory of HGMS will promote the development of HGMS technology,thereby beneficial to improve the utilization of weakly magnetic minerals.Most models in the existing theories of HGMS were established based on upstream（faced to feeding slurry）capture.As an important part of HGMS,particle capture and accumulation behavior in downstream side of matrix（dogged from feeding slurry）was often ignored.Moreover,the selectivity of HGMS failed to attract enough attentions as capture capacity.So far there were no mature theory for evaluating separation performance of upstream and downstream capture.To solve these problems,experimental and theoretical methods were used to reveal the basic principles of upstream and downstream capture.The main content and conclusions were as follows:To observe capture and accumulation process of particles on matrix’s upstream and downstream side,a visualized experimental setup of HGMS were designed on the basis of‘日’type magnetic system by drilling a hole along the axis of iron core.At the assistant of theoretical calculation and ANSYS simulation optimization,parameters like coil size,magnetic pole shape,diameter of iron core and feeding hole were designed and optimized.After manufacturing at the optimal scheme,the setup was proved to be able to provide a background magnetic field of 0.78 Tesla for the separation region around central point.The special design of supporting shaft made it possible for the magnetic system to rotate and provide uniform magnetic field at any direction.Visualized HGMS experiments of all configurations（longitudinal,transversal and axial）could be conducted in this setup by changing the direction of matrices.To investigate the separation behavior of matrix’s upstream and downstream side,experiments were conducted using different types of samples.The results indicated that when mixture of weakly magnetic particles and nonmagnetic particles was fed as raw material,nonmagnetic particles were mainly entrained in upstream deposits,which made Fe grade of downstream deposit stay at a high value.Meanwhile,when mixture of two types of weakly magnetic particles was fed as raw material,Fe grade of downstream deposits stayed low.In addition,parameters like feeding velocity,magnetic induction,size and density of the feed were influential to the weight,Fe grade and size composition of the upstream and downstream deposits to some extent.The classic particle motion equation was modified by taking the effect of gravity under consideration.For the first time ever,motion trajectories of particles around matrix under complex fluid condition were quickly solved by integrating analytical method and simulation method.Moreover,separation ratio was used to evaluate separation performance during upstream and downstream capture.The results indicated that mechanical entrainment of nonmagnetic particles was mainly caused by gravitational force.Particles with bigger gravity tended to experience a more serious entrainment.Meanwhile,nonmagnetic materials failed to be entrained in downstream deposits due to the lack of magnetic traction force.In competitive capture feeding system,all components were all subjected to magnetic force and a minor drag force,which made downstream deposit stay in low Fe grade.For the first time ever,static buildup model for downstream capture were established by taking gravity under consideration.It was testified by experiments that the model managed to predict saturated buildup profile of downstream deposits.Theoretical analysis based on this model indicated that the saturated buildup profile was dependent on radius of matrix（a）,background magnetic field（H₀）,volume susceptibility（κ）and valid density（ρ_p-ρ_f）of particles.The increment of valid density would shrink the saturated buildup profile while the effect of other parameters（a,H₀,κ）was the opposite.In addition,the diameter of particles as well as feeding velocity was found uninfluential to saturated buildup profile.Selectivity evaluation model was established based on static buildup model.It was verified that predicted results from the established model share the same tendency with experimental results.The accuracy of the model would be improved if separation performance among particles before arriving matrix could be considered.In future works,we will try to develop the selectivity evaluation model by altering the current buildup model to dynamical.In addition,customized design of matrix for specified feed would be considered according to its capturing characteristics on matrix’s upstream and downstream side.130 figures,9 tables and 119 references...