Effect Of Solid Wax/Soot Physical Deposition On The Surface Hydrophobicity Of Oxidized Coal

Coal surface hydrophobicity plays a key role in coal processing and utilization processes such as dehydration and drying,coal separation,and preparation of coal water slurry.Poor hydrophobicity of oxidized coal surface is one of the main reasons for its difficulty in utilization.The surface of oxidized coal contains a large number of oxygen-containing and nitrogen-containing functional groups,and its strong polarity makes it easy for water to spread on the surface of oxidized coal,thereby affecting the hydrophobicity and floatability of oxidized coal.This paper analyzes the changes in the surface properties of coal samples before and after oxidation.Physical vapor deposition and direct physical deposition were used to modify the surface of oxidized coal with soild wax and soot.The optimal modification conditions for the hydrophobization of oxidized coal surface were explored.Molecular dynamics was used to simulate the adsorption process of waxy molecules and carbon black molecules on the surface of oxidized coal and the presence of water molecules on the surface of oxidized coal before and after modification.An experimental study on the effect of soot on improving the flotation of oxidized coal was conducted by flotation tests,and the optimal amount of soot in the flotation process was obtained.The detail conclusions are as follows:(1)Industrial analysis,ultimate analysis,infrared spectroscopy and other analysis tests were conducted on coal samples of Jucaita coal mine before and after oxidation.It is concluded that the reason why the hydrophobicity of the coal sample surface becomes weak after oxidation is mainly due to the interaction between the alkane chain on the coal sample surface and oxygen during the oxidation process.The alkane chain breaks to form an unequal number of oxygencontaining functional groups.The content of oxygen-containing functional groups on the surface of oxidized coal increases,and the content of alkane chains decreases?(2)The physical vapor deposition test of solid wax was carried out on the surface of oxidized coal.It was concluded that the physical vapor deposition of solid wax on the surface of oxidized coal can effectively improve its hydrophobicity,and the contact angle can be increased from about 40° to about 106°.Soot particles are prepared by incomplete combustion of candles,and a soot suspension was prepared to direct physically deposit the surface of oxidized coal.The deposition of soot particles on the surface of oxidized coal can effectively improve the hydrophobicity of the surface of oxidized coal.And finally,the contact angle of oxidized coal can reach about 153°.(3)From the simulation results of the interaction between solid wax,soot,and oxidized coal surface,we can find that the binding energy of solid wax,soot,and coal surface are all positive.It means both solid wax and soot can be stably deposited on the surface of oxidized coal.(4)After the molecular dynamics calculation of the wettability model in three different cases,the diameter of water droplets spread on the surface of oxidized coal is: unmodified > solid wax deposited > soot deposited.The measured results of the contact angle indicate that the order of the contact angle is: unmodified < solid wax deposited < soot deposited(5)A flotation test was carried out on the oxidized coal sample of Jucaita.When kerosene was selected as the collector,the optimal collector dosage was 1.6 L/t.The best mixing time is 2 min.When MIBC is selected as the frother,the optimal amount of frother is 30 g/t;the optimal amount of soot is 15 g/t.