| Thin liquid film drainage process between a particle and a bubble is the key process of particle-bubble attachment.The induction time represents the time required for the liquid film to thin for the attachment of a particle to an air bubble during flotation.Induction time measurements,using the Glembotsky technique,are not completely representative of bubble–particle attachment interactions in a flotation cell;the reason is that all particles in flotation cells are in motion while the Glembotsky technique is performed using a static bed of particles.Induction time measurements in flotation cells cannot be determined using a high-speed camera due to a large number of bubbles and particles and therefore the only possibility is to use the fundamental flotation models.Additionally,as an important driving force of particle-bubble attachment process,the source and value of hydrophobic force are still unclear.Although Atomic Force Microscopy(AFM)and other methods can be used to measure hydrophobic force and thin liquid film drainage process,it is very difficult to determine hydrophobic force in the process of particle-bubble interaction,especially when the measured particle is highly irregular.The model of attachment interaction between a bubble and a particle after collision can provide a new theoretical perspective for particle-bubble mineralization in flotation process.The relationship between flotation recovery and flotation time of pyrite under different chemical conditions was obtained through microflotation experiments on pure pyrite.The relationship between flotation recovery and time and flotation rate constant were fitted with classical first-order kinetic model: R =R? ??1-exp(-kt)??,which fits the flotation kinetics of pyrite in xanthate solution well(R2 > 0.99).Bubble images were obtained by CCD high-speed dynamic camera,which were analyzed by Image-Pro Plus 6.0,Media Cybernetics.The key parameters of FinchDobby model,bubble size and bubble rising velocity,were obtained.Using FinchDobby model,the interaction of particle-bubble surface in different flow regimes(potential flow,intermediate flow and Stokes flow)and the functional relationship between flotation rate constant and flotation probability are given.The general formula for calculating critical attachment time of mobile and immobile bubble surface is given.The experimental results show that the Reynolds number of bubbles is 80.16,which issuitable for potential flow model.For mobile bubble and immobile bubble surface,the relationship between flotation rate and critical attachment time is an exponential decay(R2=0.9999).The critical attachment time between a particle and a bubble can be obtained by combining the experimental results of flotation rate.The critical attachment time on mobile bubble surfaces tends to be lower than the critical attachment time on immobile bubble surfaces.The smaller the particle size is,the smaller the settling velocity of particles is,and the results of mobile bubble surfaces and immobile bubble surfaces are similar.Based on the collision efficiency of particles and bubbles,the effect of particle size on flotation probability(collision radius)was considered.The first-order rate equation of interaction between particles and bubbles in different flow regimes was deduced: =k ??(U b +BVs)N1 N 2 P /N1.The new model can be combined with the classical Finch-Dobby model to calculate the bubble-particle interaction under different flow regimes and the critical attachment time between mobile and immobile bubble surfaces.The results show that the relationship between flotation rate and critical attachment time is an exponential decay(R2=0.9999).The critical attachment time between particles and bubbles can be obtained by combining the results of flotation rate test.For the classical Finch-Dobby model,the flotation probability has nothing to do with particle size,but the first-order rate equation based on particle-bubble collision efficiency considers the effect of particle size on the flotation probability.The experimental results show that the results of the new model are close to those of Finch-Dobby model with the increase of particle size in the experimental particle size range(from-75+38 ?m to-212+150 ?m).The sliding process of a particle on the surface of a moving bubble and its influencing factors were explored by means of CCD high-speed dynamic camera.The sliding process of pyrite particles on the surface of bubbles at different initial collision angles,pulp pH value,collector dosage and particle size was studied by means of CCD high-speed dynamic camera.The sliding time was recorded and the effect of solution chemical environment on the sliding process of pyrite particles on the surface ofbubbles was explored.The experimental results show that the initial collision angle,pH value,xanthate concentration and particle size have significant effects on the sliding process of pyrite particles on the bubble surface.The sliding time can be estimated by the following formula: t =?(pH)? 2(C)? 3 PAX(D)?4sl1 P,in which coefficients,?1,?2,?3 and ?4,are functions of the collision angle.When the collision angle is between 0o and 90 o,?2 and ?4 are positive,while the ?3 are negative,indicating that the sliding time is positively correlated with pulp pH and Dp,but negatively correlated with xanthate concentration.The sliding time obtained by experiment and calculation is in good agreement,with an average relative error of 2.18%.The correlation has strong nonlinearity and can be used to predict the sliding time in a wide range.It is helpful to better understand the attachment interaction between a pyrite particle and an air bubble in the sliding interaction process.Based on the induction time tests using Glemobtsky method,thin liquid film drainage process between an air bubble and a pyrite particle was invesitigated by using Yoon theory and Stefan-Reynolds model.A method for calculating the hydrophobic constant(K132)of pyrite-xanthate system was proposed.The Stefan-Reynolds model is solved by the fourth-order Runge-Kutta method.The spatio-temporal evolution law of thin liquid film drainage process under different given hydrophobic constants is obtained.The critical film thickness(hcr)determined by Yoon theory and the induction time determined by experiments were used to obtain the key parameter of bubbleparticle interaction process,namely the hydrophobic constant(K132).The influence of solution chemical conditions on thin liquid film drainage process was explored.The key parameters in the thin liquid film drainage process,such as induction time,hydrophobic force constant,energy barrier and critical thickness of hydration film(hcr),can be estimated by the following formula: Y=?()? 2(pH)?31Conc..The effect of chemical conditions on thin liquid film drainage process can be quantitatively analyzed by coefficient elimination method.The results show that the pH of the solution are the most significant variables(b(?3=0)?0.98).Thin liquid film drainage process between a pyrite particle and an air bubble in xanthate solution depends not only on theelectrostatic double-layer force,but also on the hydrophobic force.The liquid film and colloid force have an important influence on the attachment between an ari bubble and a pyrite particle.The feasibility of improving coal flotation desulfurization by changing the chemical environment of flotation solution was explored.The effect of starch depressant on the improvement of coal-pyrite flotation system was explored.The experimental results showed that the effect of starch depressant on pyrite and coal was significantly different under xanthate collector,and the difference increased with the increase of xanthate concentration.The adsorption characteristics of xanthate on coal and pyrite surface were analyzed by means of UV-Visibe spectroscopy and zeta potential.The adsorption density of xanthate on pyrite/coal particle surface was determined by solution consumption method.The results showed that the adsorption amount of xanthate on coal surface was much lower than that on pyrite surface.Meanwhile,the adsorption amount of xanthate on pyrite surface decreases with the increase of pH,while the adsorption amount of xanthate on coal surface is almost independent of pH.In addition,ultrasonic desliming treatment of pyrite samples is conducive to greatly reducing the consumption of xanthate in flotation process.The functional groups of coal samples were analyzed by XPS,and the hydrophilicity coefficients HA of two kinds of coal samples were determined.The results showed that,in the presence of starch depressant,there was no significant difference in the hydrophilicity of coal surface on the results of pyrite flotation.Corresponding parameters of pyrite flotation in coal such as critical attachment time,attachment probability,critical collision angle,flotation recovery and flotation rate constant can be estimated by the following formula: Y =?(.)2()3()41Conc ? pH ? HA ?(D)?5p.The effect of chemical conditions on the flotation behavior of pyrite in coal is analyzed.The results show that,in the presence of depressant,pH and particle size are the most significant variables in the flotation process of pyrite in coal,while the hydrophobicity of coal sample surface has no significant effect on the flotation behavior of separating pyrite from coal.The thesis contains 86 Figures,31 forms and 202 pieces of references. |
PDF Full Text Request