Influence Mechanism Of Particle Shape On Bubble-particle Attachment And Detachment Behavior

Particle shape is one of the important factors affecting mineral flotation recovery,and it plays an essential role in both the attachment and detachment of particles and bubbles.However,the understanding of particle shape in the flotation process is still limited,mainly due to the difficulty in accurately characterizing the fine particle shape.Other parameters such as flotation agents and pulp properties are also influential.In this thesis,particles with different shapes were selected as the research object to discuss the influence of particle shape on the flotation recovery law,and then to study the influence mechanism of particle shape on the particle-bubble attachment process and detachment process.The main results are as follows:First,the effect of particle shape on the flotation recovery and speed of both quartz and coal particles was studied.For quartz particles,non-spherical particles exhibited the highest flotation recovery,followed by the mixed particles,and the recovery of spherical particles was the lowest.Also,the effect of particle shape on quartz flotation recovery was weakened with the increase of collector dosage.For the flotation of coal particles with the same size fraction and similar ash content,the larger the elongation ratio(ER)of the particles,the greater the flotation recovery.The flotation rates of both coal and quartz particles with different shapes all conform to the first-order matrix model,and the flotation speed constant increases with the increasing ER.Second,the attachment behavior of bubbles and particles with different shapes was studied using the visualization system of particle and bubble attachment.The bubble load of the non-spherical particles was the largest,followed by the mixed particles and then the spherical particles.The attachment efficiency of regular-shaped particles decreased as follows: cubic particles,triangular prism particles,cylindrical particles,and spherical particles.Collector dosage and particle size also affect: the attachment efficiency increased as the collector's dosage increased and as particle size decreased.As the collector dosage increased,the effect of particle shape on attachment efficiency became less discernible.The colliding sites between particles and bubbles are diversified concerning the particle shape,mainly the spherical surface of spherical particles,the cylindrical surface of cylindrical particles,and the edges and vertices of cubic and triangular prism particles.After the collision with bubbles,the edge and vertices sites are prone to the bubble compared to the curved and flat surfaces.During attachment,a three-phase contact line(TPC)is formed and spreads on the curve surface of spherical particles,while a TPC is first formed at the edge of cubic particles and then spreads out onto the particle surface.The induction time of cubic particles was observed shorter than spherical particles,and the TPC was larger.Compared with the spherical surface,the edge structure promotes the thinning of the liquid film,thus facilitating the formation and spreading of the TPC.Thirdly,the effect of particle shape on the detachment behavior of particles and bubbles was studied by the detachment test in a flotation column system.The recovery of spherical particles in the collecting zone was lower than that of non-spherical particles.The detachment rate of spherical particles in the foam zone was higher than that of non-spherical particles.Bubble coalescence and oscillation are two primary forms of particle detachment in the foam zone.A visualization system of bubble coalescence and detachment was used to compare the coalescence and detachment behaviors of particles with different shapes.The results indicated that the amount of coalescence and detachment of non-spherical particles was smaller than that of spherical particles.Similarly,a visualization system of bubble oscillation desorption was applied,and the results showed that the detachment of non-spherical particles from the surface of the oscillating bubble is smaller than that of spherical particles.A larger ultrasonic amplitude was required for complete detachment of non-spherical particles from the bubble surface than that of spherical particles.While spherical and cylindrical particles attached to the bottom of the bubble mainly through the curved surface,cube and triangular prism particles were attached mainly through the flat surface.The TPC on the cubic and triangular prism particles was larger than on the spherical and cylindrical particles.A pining phenomenon was also observed on the edge structure.The detachment force of the cubic and triangular prism particles was found to be more significant.Finally,the attachment-detachment forces between different shapes particles and bubbles were studied.A theoretical model was proposed to calculate the forces between particles and bubbles based on the theory of minimum free energy,and it has been proved to be widely applicable.Generally speaking,in the attachment process,the downward force remained unchanged as the bubble gradually decreases.TPC extended rapidly on the particle surface spontaneously,and the dynamic contact angle rapidly increased to the receding angle.Then,the TPC passively spread on the particle surface slowly as the downward force gradually increasing,and the dynamic contact angle remained the same as the receding angle.In the detachment process,an upward force was expected,and after an initial increase,it gradually decreased with the rising of the bubble.At the early stage of detachment,the TPC decreased slowly,but the dynamic contact angle increased rapidly to the advancing contact angle;the later stage of the detachment was mainly manifested by the rapid decrease of the TPC and the slow increase of the dynamic contact angle.By comparing the attachment-detachment processes of the truncated spherical particle and the spherical particle with bubble,it is found that the spontaneous extending radius of TPC was larger and the passive extending speed was faster on the plane of truncated spherical particle in the attachment process.Thus,a smaller downward force was required to achieve the same maximum radius of TPC;in the process of detachment,the advancing angle,horizontal angle of the bubble,and the maximum attachment force on the plane of truncated spherical particle were larger.Compared with the spherical surface,the TPC pinning phenomenon at the intersection of truncated spherical particles during the attachment process hindered the further attachment between the bubble and the particle.However,the TPC pinning phenomenon at the intersection of truncated spherical particles during the detachment process increased the horizontal angle of the bubble and the maximum attachment force,which enhanced the stability of the attachment between the truncated spherical particle and the bubble.This paper has 124 pictures,10 tables and 174 references.