Research On Characteristics Of Oily Bubbles Flotation Process Of Low Rank Coal And Its Flotation Kinetics

China's low rank coal resources are very abundant,accounting for about 45.68%of its coal resources,clean and efficient utilization of low rank coal resources is of critical significance to protect China's energy security and economic development.Low rank coal has poor natural floatability,high consumption flotation reagent,and easy dissolution in water,resulting in hindering industrial application of low rank coal flotation.In order to solve the problem of low rank coal flotation,oily bubbles flotation method was adopted,it can effectively advance low rank coal particles mineralization and improve clean coal yield.Currently,mineralization mechanism between low rank coal and oily bubbles is dimness.In this paper,taking low rank coal slime in Shendong mining area as the object of study,intensive study flotation process characteristics and kinetics of oily bubbles floatation,discuss flotation mechanism of oily bubbles flotation,in order to provide a theoretical basis and technical support for industrialization of low rank coal flotation.Based on a series of modern analysis and test methods(SEM,FT-IR,XPS,XRD,etc.),characteristics of low rank coal are analyzed,it indicates that the low rank coal samples show characteristics of high content in fine slime and high ash content,there are many pores and depressions on its surface,the oxygen functional groups on its surface are mainly hydroxyl and ether group,also has small content of carboxyl and carbonyl.Impurity minerals in low rank coal are mainly quartz,kaolinite and muscovite,the content other mineral is less.the contact angle of coal slime with full sizes fraction is 40.8°,it belong to medium floating slime.Oily bubbles flotation technological parameter were optimized by the response surface method.Through single factor experiment and Box-Behnken experiment,optimal oily bubbles flotation test conditions combination were geted,it is flotation machine speed of 2152.50r/min,collector dosage of 4.35kg/t,pulp density of56.00g/L,and aeration quantity of 0.22m3/h,the maximum combustible recovery has reached 96.53%.The lowest limit of the reagent consumption of low rank coal using oily bubbles flotation is explored by means of model limit,the maximum combustible recovery reaches 88.32% under the minimum collector dosage of 2.32kg/t.Under the conventional flotation method with 50kg/t collector dosage,the yield of cleaned coal reaches 68.62%,and the combustible recovery rate was 88.18%.Compared with conventional flotation method,efficiency of oily bubbles flotation of low rank coaland consumption of the collector is obviously improved.From the view of flotation rate,the flotation process characteristics of ordinary bubble,cold oily bubbles and hot oily bubbles flotation and low rank coal slime with different size fractions flotation using oily bubbles were studied,it shows that the flotation rate constant of conventional flotation decreases with the flotation time,however,flotation rate constant of oily bubbles flotation increases with the flotation time,and cold oily bubbles flotation is better than conventional flotation.Atomization is beneficial to disperse collector evenly in the slurry,flashing with elevated temperature is more favorable for oily bubbles formation and particles mineralization.Flotation rate of slim with size fractions follow the order from big to small is: 0.125~0.074mm>-0.074mm>0.25~0.125mm>0.25~0.5mm,namely,the flotation rate of coal slime is the fastest with the smaller size fractions and lower ash content.The process of conventional flotation of low rank coal is close to that of the classical first order flotation kinetics model.To improve the adaptability of the kinetics model to the flotation process,adding a time parameter t* in the flotation kinetics model,the flotation process of oily bubbles flotation is more in line with the modified classical first order flotation kinetics model.The mechanism of oily bubble flotation was studied from the aspects of bubbles characteristics,kinetics and thermodynamics,it shows that the foam stability of oily bubbles is more stronger,and water entrainment of oily bubbles flotation is more smaller,Inlet flash hydrocarbon collector will reduces the number of bubbles.The induction time of oily bubbles is sharply lower than that of ordinary bubbles,increasing the oil film thickness can shorten the induction time,and the smaller the particle size has shorter the induction time,shortening the induction time will significantly improve the adhesion probability.The mineralization barrierenergy barrier between the particles and the oil bubbles is smaller,it is conducive to adhesion process.