Mechanism Of Bubble-particle Detachment At The Static Pulp/Froth Interface

The high detachment rate of coarse particles is the main reason for its low flotation recovery rate,and the detachment form and mechanism have not been elucidated clearly.The existing research on the mechanism of particle detachment is mainly concentrated in the pulp and foam zone,while the particles detachment in the pulp/froth interface zone is rarely studied.In this paper,using high-speed dynamic microscopic observation technology to established coalescence-detachment and collision-detachment test system,combining with image processing and analysis software,the bubble-particle detachment behavior and mechanism of static pulp/froth interface area were studied,aiming at providing some theoretical guidance to achieve the high-efficiency flotation recovery of coarse particles.Analysis of the samples,which obtained from the top of the foam layer to the position of-200mm in the height direction below the liquid level of the industrial flotation column,shows that the total load mass of bubble and the-1.4g/cm~3 density loading mass in the pulp/froth interface area are rapidly reduced,The yield of+0.125mm in the-1.4g/cm~3 density range decreased the fastest,and the yield of-0.074mm decreased slightly,indicating that there is a large amount of bubble-particle detachment in the pulp/froth interface region,and the detachment particles of the low-density material is mainly coarse particles.The laboratory three-product flotation column test showed that the recovery rate of the capture zone was negatively correlated with particle size,density and pulp concentration.The detachment rate of the foam zone was positively correlated with particle size,density and foam layer thickness.The detachment rate of the pulp/froth interface zone is positively correlated with the particle size,density and pulp concentration.The high-density coarse particles are firstly detached and its rate is also very high.The detachment in foam layer is mainly happen in the bottom position,that is,the pulp/froth interface area,and the worse the hydrophobicity of the particle surface,the faster the detachment rate.The static pulp/froth interface area was observed by high-speed dynamic microscopic observation technology.It was found that the main detachment form of the area was bubble coalescence-detachment.The coalescence forms are divided into horizontal and vertical ones.A new detachment was found,coalescence and collapse of the bubbles results in detachment of loaded particles on adjacent non-coalescence bubbles,which is defined as coalescence disturbance detachment.In addition,it was observed that the bubble-particles collided with other bubbles in the pulp/froth interface area,and the particles slide along the surface of the bubble,but particle detachment behavior was not observed.To simulate the bubble coalescence behavior in the high-liquid environment of the pulp/froth interface zone,two horizontal bubbles of 1.5×1.5 mm were used to load the glass beads with different particle sizes and hydrophobicity.The horizontal coalescence,vertical coalescence and coalescence disturbance were studied to study the law of detachment of particles.When the bubbles consolidate horizontally,the detachment rate of 481um particles with the contact angle of 52°is the lowest,and the second is 45um particles.The detachment rate of 120um particles is the highest.This is mainly because the damping effect of 481um particles on bubble coalescence is large.And located at the bottom end of the bubble,far from the both ends of the axis and the intermediate end of the sharply oscillated;the same particle size,the larger the contact angle,the lower the detachment rate of the particles;the different particle size,the contact angle increases,the coarse particle detachment rate.The detachment rate of the particles with the same properties decreases first and then increases with the increase of the mass of the bubble load.The decrease of the detachment rate is mainly affected by the damping effect.The increase of the detachment rate is mainly due to the decrease of the surface area of the bubbles after the coalescence.The desorption rate of the bare bubbles coalescence and the loaded bubble coalescence is lower than that of the two loaded bubbles.In the former merger process,the load bubble damping effect is obvious,and the particles move from the load bubble to the bare bubble side.When the coalescence bubbles are vertically,the detachment rate is higher than that of the bubble level under the same conditions.This is because when the vertical coalescence is performed,the load particles are mainly concentrated on the end point where the acceleration is the largest.In the case of the coalescence disturbing detachment mode,the detachment rate of the non-coalescence bubble-particles is related to the particle distance and the endpoint of the bubble axis.The non-coalescence bubble-particles have a high detachment rate when they are located at the upper portion of the vertical coalescence bubble,and have a low detachment rate at the lower portion,and the detachment ratio is between the above two forms when the bubble axis is horizontally consolidated.Image processing software was employed to analyze the bubble detachment behavior when different particle was loaded on the bubbles.When the bubble loading is large,the particle detachment mainly occurs when the bubble is coalescence for the first time and the detachment rate is the highest at both ends of the axis.Further calculation of the acceleration of the end point and the intermediate end point of the"contraction-expansion"of the coalescence bubble indicates that the acceleration of the end point and the intermediate end point of the liquid film at the time of the first contraction of the horizontal direction is 59.42times and 12.7 times of the acceleration of gravity,respectively,and then acceleration value decreases rapidly.The calculation results corroborate the observations.When the particle loading is small,particle detachment tends to occur at the abrupt change of bubble deformation.It is because that,in the initial stage of coalescence,when the liquid film expands from the middle to the sides,the lower contour of the bubble abruptly changes.The location of the mutation is prone to detach results from the radius of curvature decreasing and the liquid film shrinking.The collision-detachment behavior of bubble-particles at the pulp/froth interface was simulated by using two kinds of test systems:lifting bubble-particle collision with liquid surface collision,lifting bubble and fixed bubble-particle collision.The results show that the collision detachment occurs only when the bubble size is large enough(2-3mm),rapid rise rate and low particle hydrophobicity.During this processing,detachment rate is quite low.The study of kinetic energy conversion of loaded particles shows that only 1.26%of the rising floating energy is converted into sliding mobile energy.The radial force analysis of the particles using the D'Alembert principle shows that the radial resultant force of the sliding particles is higher than the horizontal axis position of the bubble,and the maximum radial acceleration of the particles is 1.65 times of the gravitational acceleration.The value is only1/36 of the maximum acceleration experienced by the merger.The comparison of the magnitude of the acceleration indicates that the coalescence detachment is the main form of detachment in the pulp/foam interface zone.There are 112 drawings,22 tables,and 122 references in this paper.