Study On The Effect Of Surfactant Selective Adsorption/Desorption On The Floatability Of Low Rank Coal

The surface of fine-grained low-rank coal is rich in oxygen-containing functional groups and exhibits strong hydrophilicity.It is difficult to recover efficiently by conventional flotation methods,which restricts the economic benefits of coal enterprises and causes a large waste of coal resources.Surfactants with amphiphilic structure can effectively cover the oxygen-containing functional groups on the surface of low-order coal and improve their floatability.In this paper,based on the different adsorption mechanism and adsorption characteristics of surfactants in organic matter and minerals in low-rank coal,taking dodecyl primary alcobol ethoxylate ether(C₁₂EO₁₅)and weakly caking coal in Inner Mongolia Harwusu open pit mine as an example.The effects of ultrasonic pre-treatment on the physical and chemical properties of low-rank coal were investigated by microcalorimeter and FTIR.The adsorption characteristics of C₁₂EO₁₅ on low rank coal and gangue surface were investigated.Finally,the surfactants adsorbed on the low-rank coal are selectively removed by ultrasound to expand the difference in surface wettability between the organic matter and the minerals in the low-rank coal,thereby improving the quality of the clean coal.The main research contents of the thesis are as follows:1.Ultrasonic has a certain crushing and cleaning effect on the slime particles,which can reduce the particle size of the coal particles.After the low-rank coal is pretreated by ultrasound,hydrophilic groups such as hydroxyl groups?-OH?and carboxyl groups?-COOH?on the surface of the coal are reduced.The water wetting heat was gradually reduced from 7.69 J/g to 0.49J/g in 4 min.Ultrasound can also neutralize the charge on the surface of coal particles,reduce the negative charge on the surface of the particles,and lower the pH of the slurry.In addition,long-term ultrasonic pre-treatment may result in a decrease in the yield of low-rank coal flotation concentrate.2.At the initial stage of adsorption,the adsorption rate of C₁₂EO₁₅ on low-rank coal and gangue is very large,reaching a high adsorption amount in a short time,and then the adsorption rate is gradually reduced,respectively reaching equilibrium adsorption amounts of 4.23 mg/g and 0.29 mg/g.After the low-rank coal adsorbed C₁₂EO₁₅,the hydrophobicity was significantly enhanced,and the floatability was improved,but there were still some defects.The surfactant also adsorbs on the organic matter in the coal and also adsorbs on the inorganic surface,which leads to an increase in the yield of the clean coal and a certain increase in the ash.The adsorption and flotation test of gangue adsorption surfactant show that the adsorption of C₁₂EO₁₅ on the inorganic surface of low-rank coal is one of the main reasons for the increase of flotation ash content in clean coal.3.Ultrasound can selectively remove C₁₂EO₁₅ adsorbed by low-rank coal and gangue.Flotation experiments of low-rank coal showed that the perfection of flotation reached a maximum at 90s after ultrasonic desorption.In the experimental temperature range,the appropriate increase in temperature is beneficial to the re-adsorption of C₁₂EO₁₅ on the gangue to the low-rank coal after ultrasonic desorption,further expanding the difference in hydrophobicity between the organic matter and the inorganic surface in the low-rank coal.Properly increasing the temperature increases the yield of flotation clean coal and reduces the ash,effectively improving the floatability of low rank coal.The synergistic effect of ultrasonic and ethanol leads to a large desorption of C₁₂EO₁₅5 on the surface of low-rank coal and gangue.Although the yield of flotation clean coal is reduced,the effect of ash reduction is obvious and has certain utilization value.