The Mechanism Of Co-strengthening The Flotation Interface Of Low Rank Coal By C-O/Si-O Compound Collector

Low-rank coal is abundant in China and accounts for the largest proportion of proven coal reserves,which is of great significance to ensure energy security and promote the development of national economy.The high content of oxygen functional groups and poor hydrophobicity on the surface of coal hinder the adsorption,spreading of conventional collectors on the coal surface and bubble-particle attachment,resulting in low flotation efficiency,large collector consumption and poor economic benefits.At present,polar reagents are used to strengthen the interaction between collector and coal,but the spreading property of collector at flotation interface is neglected,which leads to less effective flotation.From this point of view,based on the strong adsorption characteristics of carbon-oxygen reagents and the super-spreading characteristics of siloxane,the C-O/Si-O compound collector was designed to take into account the adsorption and spreading of the agent on the coal surface,and the cooperative strengthening mechanism of the compound collector on the flotation interface of low rank coal was explored.Hong Liu low rank coal slime was selectesd as the object by combining macroscopic test with microscopic molecular dynamics simulation.Firstly,the surface and interface characteristics of coal slime were explored and on the basis of them,the difficulty-floating mechanism was studied.Secondly,the interfacial control of coal slime by carbon-oxygen reagent and the selective action of aromatic ester on low-rank coal slime,and the spread characteristics of siloxane reagents on coal surfaces were analyzed.Finally,the cooperative strengthening mechanism of C-O/Si-O compound collector on flotation interface of low-rank coal was concluded.It was found that the high content of fine grain aggravated sludge,and rough coal surface with high content of oxygen functional groups accelerated the hydration of low-rank coal slime.The molecular structure of Hongliu coal was constructed by a series of analysis methods,and the molecular formula was C₁₄₅H₁₀₇NO₂₂S with 2245molecular weight.The hydration mechanism of the low rank coal was studied and it showed that a large number of hydrogen bonds,mainly formed by carboxyl groups,were formed between coal and water molecules.The mobility of interfacial water in the system was lower than that of bulk water,so there was a dense hydration film on the low-rank coal surface.The bond energy of C-O is less than C-C,which is easier to be broken and form polarization;the bond angle of Si-O-C is 143°,which makes it easy to rotate between Si-O and form"super spreading"molecules;the functional groups of C-O,as well as Si-O,have higher electronegativity,a stronger ability to attract or share electrons.From the macroscopic and mesoscopic dimensions,the adsorption characteristics of carbon-oxygen reagent on coal surface were revealed,and the adsorption amount of oxygen-containing polar oil reagent was higher than that of non-polar reagent.The order of increasing in hydrophobicity of coal slime surface by carbon-oxygen agent is:DBP>DTAB>Methyl dodecyl ester>6501>Dodecyl>Dodecane.Appropriate dosage of amphiphilic medicament(6501)can reduce the polar composition of coal surface,reduce wetting heat of coal-water,and then improve the hydrophobicity of coal surface;when the dosage is excessive,the reagent molecule will adsorb on the coal surface double layer or form micelles,and then reduce the hydrophobicity of coal surface.The molecular simulations show that the polar groups of carbon-oxygen reagents play a key role in the adsorption of agents at the coal-water interface.The polarity is basically adsorbed on the coal surface,and the alkyl chain extends to the water phase,which is the result of the action between carbon-oxygen groups in reagent and oxygen-containing groups in coal and the?-?bond stacking in the reagents.The interaction energy of carbon-oxygen reagent and coal is dominated by Van der Waals energy,and electrostatic energy accounts for less.Among the reagents,DBP has the strongest interaction energy with the coal surface and is more closely adsorbed with coal molecules,prevents the water molecule from infiltrating into the coal structure,and drives water far away from the coal surface with hydrophobic chains as well,which significantly reduced the number of hydrogen bonds between coal and water.The adsorption amount and wetting rate of aromatic ester(DBP)on low density(1.3 g/cm³)coal samples were significantly larger than that of high density(1.8 g/cm³)coal samples,and the effect of DBP on the hydrophobicity of low density coal was greater.The results of AFM mechanical tests showed that the force between DBP and coal particles(46.1 n N)was stronger than that with Si O₂ particles(2.3 n N).Through the theoretical analysis of DLVO and EDLVO,the hydrophobic operation of coal particles DBP was improved significantly.As a result,aromatic ester DBP has a good targeting for slime action.The siloxane with different alkane chains was synthesized by addition reaction,and their excellent spreading performance was both demonstrated under air and liquid phase.The siloxane droplets exhibited better spreading ability on both the hydrophilic and hydrophobic substrate surfaces,in the air,attributed to the lower surface tension and the stronger concentration Marangoni effect at the gas-liquid interface.In the liquid phase,the addition of alkane chain can reduce the interfacial tension of the reagent-water,and the interaction of alkane chain and the coal enhances the droplet Marangoni effect and improves the spreading performance.In addition,the hydrophobicity and drainage effect of the alkane chain also promotes the spreading of the agent on the coal surface.The excellent spreading property of siloxane was demonstrated from molecular scale.The C8Si3 with linear structure can be spread almost completely on the coal surface by monolayer because of the small steric hindrance in the diffusion process.While,due to the effect of?-?bonds between molecules,the movement of DBP molecular was restricted,resulting in poor spreading.Compared with dodecane and DBP,12CSi3 has the largest spreading area and uniform thickness at the coal-water interface in the presence of water molecules.The addition of siloxane to alkane chain can strengthen the coal-bubble action,reduce the induction time,increase the coating angle,and improve the flotation effect.A compound reagent of aromatic ester and siloxane with appropriate alkane chain length can improve the interaction energy of coal-agent and repulsion of interfacial water,among which DBP/12CSi3 compound reagent shows the best synergistic effect.The composite reagent can further promote the coal mineralization process,increase the three-phase wetting line length between the bubble and the coal base plate,improve the bubble-coal particle attachment,and help to increase bubble-coal particle detachment force and the stability of the coal-bubble action.The flotation effect with aromatic ester/siloxane compound reagent was more improved than that of the single,and the combustible recovery rate of clean coal reached78.65%,and the ash content of that was 11.57%,when the 1:1 ratio was combined at the total amount of 4 kg/t.When the diesel oil/DBP/12CSi3/6501 as the compound collector with 2 kg/t dosage,the recovery rate of clean coal is 71.43%,and the ash content of that is 11.87%,which has the value of popularizing industrial application.The flotation test also verified the synergistic effect of C-O/Si-O reagents on the control of flotation interface of Hongliu low rank coal.