Formation Mechanism Of Oil Bubble Induced By Compound Collector And Its Effect On Flotation Of Low Rank Coal

Low-rank coal has poor natural floatability due to the large number of oxygencontaining functional groups and pores on the surface of low-rank coal.The conventional collectors are difficult to adsorb on the surface of low-rank coal and a porous structure of coal surface needs large consumption of collectors.At present,compound collectors are mostly used to strengthen flotation of low-rank coal.Thus,in this article,octane and n-caprylic acid,which is typical hydrocarbon oil and carboxylic acid collector respectively,were used to study the mechanism of compound collectors in enhancing low-rank coal flotation.From the point of view of compound collectors inducing the formation of oil bubbles,the spreading behavior of different collector droplets on bubbles and the factors affecting the spreading behavior of collectors were studied.The mechanism of the compound collector strengthening the adhesion and adsorbtion between the bubbles and coal particles was revealed,which provides a theoretical basis for the efficient flotation of low-rank coal.This study took the lump clean coal and raw coal from Daliuta as samples.In the raw coal,the-0.045 mm particle size accounts for 65.63%,the ash content of the raw coal is 23.94%,high in fine slime and ash content.Surface hydrophilic functional groups were mainly C-O(ether or hydroxyl),C=O(carbonyl or ester).The main gangue minerals were quartz,kaolinite and calcite.The formation behavior and mechanism of oil bubbles in solution were studied.The addition of carboxylic acid collectors could effectively reduce the oil-water interfacial tension and surface potential,and the interfacial tension gradually decreased with the increase of the proportion of carboxylic acid collectors.Stefan Reynolds model was used to calculate the film thinning time of different collectors.The results showed that the film thickness between the collector droplets and bubbles became thinner with the increase of time.At the same time,with the decrease of droplet-bubble diameter ratio,the film thinning speed increased and the film thinning time shortened.The higher the viscosity,the slower the spreading velocity.For the same size bubbles,the smaller the oil droplet size was,the faster the spreading velocity was,and it was easier to promote the formation of oil bubbles in the flotation process.The interaction between low-rank coal surface and oil bubble was studied.The relationship of induction time of coal samples with different collectors was: n-octane >n-octanoic acid > MC(6:4)> MC(9:1)> MC(1:1)> MC(7:3)> MC(8:2).N-octane and n-octanoic acid can act on the hydrophobic and hydrophilic sites of low rank coal,respectively.Under the synergistic effect of the n-octane and n-octanoic acid,the induction time of bubble-coal surface could be shortened,and the adhesion between bubble and low-rank coal could be enhanced.Due to the small energy barrier between the oil bubble and the coal slice,the induction time between the oil bubble and the coal surface was shorter than that between the air bubble and the coal surface.Moreover,the oil bubble had stronger stability,and the acceptable stretching degree was larger in the desorption process.In the desorption process,the oil bubble had higher activation energy E1 and desorption work E2,so the adhesion between the oil bubble and the coal surface was stronger than that between the air bubble and the coal surface,forming a stronger polymer.Edlvo theoretical calculation results showed that in the long-range force range,the interaction between n-octanoic acid and compound collector oil bubbles and coal particles had no obvious advantage over that of n-octane,but in the short-range force range,under the influence of hydrogen bond force,the interaction gravity between compound collector oil bubbles and coal particles was obviously enhanced,which made the oil bubbles adhere more firmly on the surface of coal particles.The conventional flotation test and oil bubble flotation test of low-rank coal were carried out with hydrocarbon oil-carboxylic acid collectors.The results showed that under the same experimental conditions,the combustible recovery of different collectors in the oil bubble flotation test was better than that of the conventional flotation test.The results showed that n-octane and n-octanoic acid acted on the hydrophobic and hydrophilic sites of low-rank coal surface respectively,and spread on the bubble surface to form stable oil bubbles.Based on the dual effects on coal particles and bubbles,the collecting property for low-rank coal could be improved on the premise of ensuring good selectivity,and the optimal flotation condition was 3 kg/t MC(8:2),the ash content of clean coal was 7.71%,and combustible body recovery was44%.There are 60 pictures,12 charts,and 97 references in this paper.