Study On Interface Characteristics Of Low-rank Coal Flotation And The Mechanism Of Reagent Collection

China is rich in low-rank coal reserves,and its efficient utilization is of great significance to support China’s energy security.Compared with the high-rank coal,the interface composition and structure of the low rank coal are complex,and the mechanism of the agent action is not clear,so the interface mechanism of the collector still needs to be further studied.In this paper,Shendong long flame coal and Mengdong lignite are two typical low-rank coal as the research object.The theoretical calculation,molecular simulation,test characterization and flotation test are used to study the interface Properties of low-rank coal that is difficult to float,the mechanism of hydrocarbon oil collection and the flotation behavior of compound collection,which provide the theoretical basis for the flotation collection of low-rank coal.The interface Properties of low-rank coal and its hydration are studied.There are many oxygen functional groups on the surface of low-rank coal,while the surface is rough,cracks and pores are developed,and it is easy to hydrate.The induction time of low-rank coal particles,bubbles and collectors is studied by using induction time measuring instrument.The adhesion/desorption behavior of particles group and bubble/oil drops in flotation environment is simulated,and the adhesion/desorption mechanism of low-rank coal particles,bubble/oil drops is revealed by using molecular dynamics simulation.The hydration characteristics of low-rank coal were studied.It was found that the water molecules adsorbed on the surface of low-rank coal formed a large overlap at the water/coal interface,and a large number of hydrogen bonds were formed between water molecules and low-rank coal molecules.The adsorption affinity of water molecules for oxygen-containing sites was stronger than that for carbon containing sites,and the mobility of water at the interface was lower than that of bulk water.The molecular dynamics simulation of contact angle showed that the contact angle of coal is small and could be wetted by water easily,which is consistent with the test results.The interface behavior and interaction mechanism between hydrocarbon oil collector and low-rank coal are revealed.Several methods,such as molecular dynamics simulation,FTIR,GC/MS,Zeta potential,XPS,contact angle,Wrap angle,induction time,flotation test,were used to carry out a systematic study.The results of simulation and test show that dodecane is difficult to be adsorbed and spread on the surface of low-rank coal;the adsorption strength of diesel and other hydrocarbon oil on the surface of low-rank coal is small,the effect on oxygen-containing sites is weak,the dosage of reagents is large,and the flotation performance is poor.The flotation behaviors of pure compound agents and mixture/waste oil collectors were studied.The experiments of the mixture of pure compound agents(dodecane)with esters,alcohols and carboxylic acids were carried out.The adsorption behavior of single and mixed oil collectors at the surface of low-rank coal was revealed.Shale oil,used lubrication oil,vegetable oil,animal oil,gutter oil and other mixtures/waste oil were selected as low-rank coal flotation collectors to carry out the flotation contrast test.Shale oil has strong selectivity,low dosage and good effect.Used lubrication oil can be well adsorbed on the coal surface,which can improve the flotation yield and flotation speed of coal,vegetable oil,animal oil and ground.The flotation indexes of bio oil such as ditch oil are better than that of mineral oil.Compared with traditional hydrocarbon oil collectors,mineral oil and bio oil have advantages in combustible recovery and selectivity.The adsorption structure of single collector and mixed collector was revealed.Through molecular dynamics simulation,low-temperature freeze-drying,low field nuclear magnetic resonance and other technologies,the synergistic adsorption and pore effect of the composite agent on the surface of low-rank coal were studied.The adsorption behavior of the collector on the surface of low-rank coal was studied.Dodecane molecule adsorbs on the carbon atom only,which is difficult to cover the surface of hydrophilic oxygen-containing functional group.Dodecanoic acid molecule is easy to self assemble,which reduces the coverage of dodecanoic acid on the surface of oxide graphite and increases the consumption of the collector.The mixture of dodecane and dodecanoic acid has good dispersion,which significantly improves the oxygen content.The coverage of functional groups,under the directional action of dodecanoic acid molecules,dodecane molecules can be adsorbed on the oxygen-containing sites,and the polar nonpolar compound has a synergistic effect.The diffusion law of oil collector on the surface and pore of low-rank coal is studied,and the mechanism of reducing the amount of compound collector by sealing effect is revealed.The composite agent can form oil film on the surface of low-rank coal or gather at the neck of pore to prevent the ineffective adsorption of collector inside the pore.The flotation mechanism of low-rank coal with mineral oil and bio oil collectors was studied.Shale oil has high viscosity,high content of hydrocarbons and alkenes with long carbon chain,which can improve the surface hydrophobicity of low-rank coal;used lubrication oil contains both polar and non-polar components,and the metal ions in used lubrication oil can strengthen the adsorption of polar collector on the surface of low-rank coal,forming a synergistic effect;there is a large difference in the polar component content of plant oil collector,and the types of chemical components in plant oil is little,the proportion of carboxylic acid in peanut oil and soybean oil is high,the proportion of olefin in olive oil is high,the activity of these two main components is high;the main component of animal oil is oleic acid,which can be used in combination with other chemicals;the main component of gutter oil is esters,the flotation performance is good,because of the synergistic effect of polar non-polar components and the targeting of ester compounds.In this study,the flotation collection law of mixed oil/waste oil is matched with the interface mechanism of pure compounds and flotation test results,which provides technical support for the theoretical research and engineering application of low-rank coal flotation reagents.There are 96 figures,32 tables and 162 references in this paper.