Study On Foam Stability Mechanism Of Low Rank Coal Flotation Enhanced By Mixed Surfactant

Floatation is an important way to realize selective separation of coal and gangue utilizing the difference of particle surface hydrophobicity.It is an important method to improve and utilize fine coal resources.The formation and stability of foam are the important factors that affect the recovery rate and selectivity of coal flotation.At present,it's common to use fusel surfactants to improve foam stability in coal slime flotation.The study shows that the mix use of short chain and long chain surfactants have strong foam stability,which can achieve better flotation recovery and selectivity,but the intrinsic mechanism of foam stability is not yet clear.In view of this,three kinds of alcohol surfactants with different carbon chain length(pentanol,methyl isobutyl carbinol,MIBC,octanol)were mixed with long chain polyethylene glycol(PEG)at different mass ratios to explore the effect of mixed surfactants on the flotation efficiency of slime and the stability of three-phase foam.By studying the macro foam stability of mixed solutions and the kinetics of liquid film drainage at the micro scale,the stability mechanism of mixed surfactants in enhancing flotation froth is revealed,which provides technical support for the regulation of the stability of coal flotation froth.The effects of single and mixed surfactants on the flotation of coal slime were studied.When the dosage of surfactant was less than 500 g /t,the clean coal yield and flotation rate of three short chain alcohols were higher than that of PEG;when the dosage of surfactant increased to 1000 g /t,the clean coal yield and flotation rate of PEG were significantly higher than that of short chain alcohols.The reason for this phenomenon might be due to the long length of non-polar group of PEG.When the PEG's dosage is low,a large number of PEG molecules adsorbed on the coal surface,resulting in a decrease in the number of PEG molecules on the surface of the bubbles,which weakens the regulation of foam stability,causing a low flotation yield.The floatation yield of clean coal with mixed surfactants was significantly higher than that of short chain alcohols but lower than that of PEG.The effect of mixed use of pentanol and PEG is better than MIBC and octanol,because the stability of three-phase foam in pentanol and PEG mixed solution is the strongest.Under the condition of single surfactant and mixed surfactant,the ash content of clean coal is basically unchanged and the flotation selectivity is the same.The surface tension of single surfactant solution and mixed surfactant solution was measured by means of surface tension meter.The surface tension of the solution decreases with the increase of surfactant concentration,and the order of surface activity is PEG > octanol > MIBC > pentanol.In the mixed surfactant system,the surface tension of the solution decreases with the increase of PEG component,and the value of surface tension is significantly lower than that of short chain alcohol and slightly higher than that of PEG.Mixed solutions of pentanol and PEG had the strongest ability to reduce the surface tension of the solution.The bubble size distribution is studied by bubble morphology observation system.It is found that there are more large bubbles in deionized water,and the size of bubbles decreases with the addition of surfactant.Inhibition of bubble coalescence is the main reason for the decrease of bubble size,and the ability to inhibit bubble coalescence is consistent with the variation of surface tension.The size of bubbles in mixed surfactants solution is significantly smaller than that in single solution.The mixed solution of pentanol and PEG inhibits the ability of bubble merging.The stability of foam is the strongest,and the flotation efficiency of low-ra nk hard to float coal is the best.The macro scale foam stability was studied by foam stability test device.The foaming ability and foam stability of the four surfactants decrease in the order of PEG,octanol,MIBC and pentanol.The foam stability of three kinds of short chain alcohol and PEG mixed system is significantly stronger than that of short chain alcohol but weaker than PEG,indicating that the mixing of surfactants has certain synergistic effect,and PEG performance dominates.Among them,the mixed solution of pentanol and PEG has the strongest foam stability,followed by MIBC and PEG,and that of mixed solution of octanol and PEG is poor,which is the main reason of the difference of flotation recovery rate of mixed surfactants.The dynamics of liquid film drainage between bubbles of single surfactant system and mixed surfactant system was studied by flotation foam film analyzer.The foam film between bubbles in deionized water breaks at the central point after thinning in which the breaking time is 0.69 s and the critical breaking thickness is18.65 nm.The addition of surfactant can significantly slow down the thinning rate of foam film,increase the life and improve the stability of foam film,all of which are realized by reducing the hydrophobic force of the system.The foam stability of the four surfactants was PEG > octanol > MIBC > pentanol.The results show that the liquid film drainage rate of mixed surfactant solution is significantly lower than that of short chain alcohol solution,which is close to that of PEG solution.The mixed solution of PEG and pentanol had the best foam stability.This is because the maximum surface tension gradient is formed by the maximum difference of the surface activity of pentanol and PEG,and the surfactant reflux is strong.Therefore,the increased Gibbs-Marangoni effect of the solution enhances the foam stability.There are 73 pictures,10 tables and 96 references in this paper.