Study On Ultrapure Preparation And Conductivity Of Anthracite

Transforming coal from a low-end fuel to a high-end carbon material is an important way under the strategic goal of"carbon peaking and carbon neutrality".As a coal with high carbon content,anthracite coal could have been used as the main raw material for the manufacture of conductive materials,but the large number of ash-forming minerals in coal restricted the development of coal-based conductive materials industry.In this thesis,low-ash anthracite was taken as the research object,and the mineral composition and physical occurrence forms of coal matrix and minerals were characterized by X-ray fluorescence spectroscopy,X-ray diffraction and scanning electron microscopy（SEM）-energy spectrum,so as to explore the particle size range of sufficient dissociation of the coal sample.Falcon centrifugal separation was used to prereduce the ash of raw coal,and then triboelectric separation and acid solution were used to prepare the ash reduction coal samples,and the ash reduction of 0.74%of ultra-pure anthracite and 0.13%of ultra-pure anthracite were obtained,the ash reduction effect is better.At the same time,the influence of different operating parameters on the triboelectric separation effect was studied,and the significance of the interaction of various factors on the cleaned coal ash content and yield of ultra-pure anthracite was clarified.The results show that too low or too high air volume is not conducive to separation.With the increase of voltage,the cleaned coal ash gradually decreases and the yield gradually increases.Under the conditions of voltage:12k V,air volume:65m3/h,feeding time:240s,the cleaned coal ash can be reduced to 0.74%,the yield can reach 31.16%,and the sorting effect is the best.The effect of feed speed on the sorting effect is not obvious.And the interaction of three factors on cleaned coal ash content and cleaned coal yield weight is:voltage>air volume>feed speed.The powder four-probe resistivity test instrument was used to explore the influence of moisture content,ash content,particle size and other factors on the change law of anthracite resistivity and conductivity,and the significance of the combined effect of several factors on anthracite conductivity.The experimental results show that the conductivity gradually increases with the increase of moisture content.With the decrease of its own ash content,the conductivity gradually increased,when it dropped to 1%,the conductivity increased sharply with the decrease of ash,and under the conditions of ash content of 0.13%,moisture content of 8.53%and particle size of 0.2-0.1mm,coal sample conductivity was the best,and the conductivityσwas17.53×10^-8 S/cm.When the external pressure is increased,the conductivity gradually increases;Within the scope of investigation,particle size had little influence on conductivity change.At the same time,the conductivity of common minerals is:pyrite>kaolinite>silica>calcium carbonate>calcium sulfate.Under the interaction of several factors,the size of the influence on anthracite conductivity is as follows:ash>moisture content>particle size.The conductivity of anthracite was improved by heat treatment,and the conductivity of anthracite under heat treatment was explored.The results show that the conductivity increases when the heat treatment temperature increases.Increase the ash content of the sample,and the conductivity decreases;The change of ash content affects the conductivity of anthracite coal more obviously than the change of temperature.The changes of product structure and functional groups in the process of heat treatment and the changes of mineral content in anthracite before and after heat treatment were obtained by means of infrared spectroscopy and scanning electron microscopy-energy spectrum analysis.The analysis results show that kaolinite is the main mineral enriched in anthracite.When the temperature rises to 500°C,cracks occur on the surface of the coal sample,and a small amount of minerals exist.With the increase of temperature,the cracks on the surface of coal sample become larger and the accumulated mineral crystal particles become more.When the temperature reaches 1000～1200°C,the minerals basically disappear.It can be seen from the data that the contents of Si O₂ and Al₂O₃ in coal have increased,while the contents of Na₂O,K₂O and sulfur elements have decreased significantly.The content of alcohol,phenolic-OH and-NH₂ functional groups in the anthracite structure increased with high temperature,in which the carboxyl group and carbonyl group were removed,and most cycloalkanes were gradually aromatized after deoxidation.Finally,it can be seen from the test results that compared with the conductivity of anthracite itself,the conductivity of anthracite increases nearly 10¹⁰ times under the action of heat treatment,which plays a qualitative role.When the heating temperature reaches 800°C and the ash content of the sample is 0.13%,the resistivity of anthracite products is 0.06Ω·cm and the conductivity is 1587.30 S/cm,which has good electrical conductivity and is expected to be used in coal-based conductive composite materials.