Study On The Mechanism Of Slime Coating Based On In-situ Characterization

The phenomenon of slime coating in flotation process is one of the main factors causing the decrease of floatability of valuable minerals and the pollution of concentrate products.Due to the limitation of characterization methods,the research on slime coating mainly focuses on the property of mineral interface.The mechanism of slime coating driven by mineral interface properties and hydrodynamic conditions is still unclear.The systematic in-situ study of slime coating in turbulent environment is helpful to clarify the process of slime coating,improve the theory of slime coating,and provide a new idea for the inhibition of slime coating and the improvement of mineral flotation.In this study,an in-situ visualization test system for slime coating was established by Particle Vision and Measurement(PVM)technology to study two common heterocoagulation systems:mineral particle-plane and mineral particle-sphere.A characterization system for measuring the degree of slime coating in turbulent field was established by using Focused Beam Reflectance Measurement(FBRM).The degree of slime coating under different experimental conditions was quantified,and the kinetic law of slime coating process was analyzed.Combined with the analysis of experimental results,the mechanism of slime coating in turbulent field was discussed.Finally,the effect of gangue mineral species,gangue mineral concentration and gangue mineral size on slime coating and coal floatability in the coal-gangue mineral mixed pulp system was studied.The inhibiting effect of flow field regulation on slime coating was investigated.The effects of interparticle interface force,surface roughness and shear rate of flow field on slime coating were explored in the study of in-situ visualization of slime coating.The results show that the interfacial forces determine the slime coating behavior under the same hydraulic conditions.It is found that surface roughness can affect the interfacial forces between minerals,the degree of slime coating decreased with the increase of roughness.At the same time,it has been preliminarily confirmed that the slime coating behavior is affected by the interaction of mineral interface force and fluid dynamics,and the significant influence of the local regional flow field characteristics on the slime coating behavior has been observed in-situ.In the kinetic study of slime coating process,the effect of DLVO force on the slime coating degree was firstly studied.The results show that adjusting the p H value of pulp,adding sodium hexametaphosphate and changing the concentration of Na~+ions can all change the electrostatic double layer force,and affect the maximum slime coating degree.Then the effect of hydrophobic force on slime coating was discussed.The results show that the hydrophobic force should be considered when the mineral surface has a high degree of hydrophobicity.Meanwhile,the effect of the shear rate of the flow field on slime coating is studied.It is found that the slime coating degree between quartz and coal particles decreased with the increase of shear rate.However,the slime coating still existed even at a high shear rate,when there is a strong attraction between the two mineral particles.When an obvious slime coating occurs between minerals,the slime coating degree increased rapidly with the reaction time,then the rate of increase slows down and finally leveled off.The variation trend is consistent with the classical first order dynamics equation.In the study of the slime coating mechanism in turbulent field,the effect mechanism of shear rate and eddy scale on slime coating were analyzed.The interaction process of heterogeneous minerals in the slime coating was divided into three stages:collision,attachment and detachment.The related probability equation of heterocoagulation was established.Then,a theoretical analysis was made on the inhibition of slime coating based on the probability equation.The results show that reducing the attraction between particles and increasing the kinetic energy of particles are effective means to inhibit the slime coating.It is necessary to combine chemical control with flow field control.The influence of quartz,kaolinite and illite on coal floatability after the slime coating of gangue minerals and coal particles was investigated.The results show that the three gangue minerals can cover the surface of coal particles,leading to the poor floatability of coal.Illite and coal have the highest slime coating degree,which has the greatest influence on the coal floatability,followed by kaolinite and quartz.The difference of the slime coating degree between gangue minerals and coal mainly depends on the interaction force.The slime coating degree increased significantly with the increase of gangue mineral content.Two clay minerals(illite and kaolinite)can affect the coal floatability at lower concentrations than quartz.The increase of the flow field intensity can reduce the slime coating degree and weaken the adverse effect on coal floatability.Adding dispersants to reduce the interaction force between clay minerals and coal can effectively inhibit the occurrence of slime coating under the high intensity flow field.But dispersants can also adsorb to the coal surface and reduce its floatability.Therefore,the selection of appropriate dispersant with flow field control is an effective method to inhibit slime coating.This paper contains 105 pictures,22 tables,and 167 pieces of references.