| Carbon neutrality and carbon emissions peak policies have led to the need for industrial restructuring and adjustment in the coal industry.It is very important for the coal industry to make efficient and clean use of coal.Coal product quality management,as an important part of the modernization process of coal processing plants,has an important impact on the production of downstream industries.One of the difficulties in coal quality management is the moisture of flotation concentrate coal.Mechanized coal mining and new coal beneficiation processes aggravate the problem of coal dewatering.The properties of the macerals,as the main component in the flotation concentrate,will certainly have a significant impact on the dewatering of the concentrate.In this dissertation,the macerals of a difficult-to-dewatering subbituminous coal were taken as the object of study.First,the differences in the structural properties of different macerals were investigated by using 13C NMR and FTIR instruments.Based on the properties and simulation of the macerals,the structural models of the macerals were constructed.The dewatering mechanisms of macerals were also described.Then,by analysing the maceral surface properties,floc size and filter cake structure,as well as molecular and mesoscale simulations,the mechanisms and synergistic effects among flocculants,surfactants and those two filtering aids to enhance the dewatering of the macerals were investigated.Finally,by fitting the macroscopic dewatering index and microscopic property parameters,the filtering mechanism of the filtering aid for different macerals was revealed.The main conclusions obtained are as follows.（1）The differences properties of the macerals resulted in different dewatering behavior.Compared with the vitrinite,the inertinite has a slower filtration rate and higher cake moisture.By studying the properties of the above macerals,it was found that the vitrinite had fewer hydrophilic functional groups,better hydrophobicity,and lower surface charge.This not only facilitated the agglomeration of particles to form a loose filter cake structure,but also would reduce the capillary pressure required for dewatering,reduce the adsorbed water content,and thus obtain faster filtration speed and lower moisture.In addition,the difference in chemical structure makes the inertinite easier to break into fine particle,which also negatively affects the filtration speed and cake moisture to some extent.（2）Flocculants can effectively promote dewatering performance,but the dewatering mechanisms are different for the two macerals.It was concluded that the flocculant reduced the vitrinite cake moisture mainly by improving the filter cake structure;and reduced the inertinite cake moisture by enhancing the hydrophobicity.The results of X-ray photoelectron diffraction and other instrumental analyses and simulations showed that the adsorption behavior of flocculants on the macerals surface is different,which leads to different agglomeration effects and filter cake structures,and thus affects the filtration aid effect of flocculants on macerals.At the optimal dose of 30 g/t,the water content of the mirror and inert groups decreased from 23.25%and25.86%to 20.45%and 21.03%,respectively.（3）Different surfactants have different dewatering performance and mechanisms on different macerals.It was concluded that the surfactants mainly reduced the vitrinite cake moisture by improving the filter cake structure,thus the polyoxyethylene lauryl ether had the best filtration aid effect on the vitrinite.For the inertinite,surfactants reduce vitrinite cake moisture mainly by reducing the surface tension of the solution and improving the hydrophobicity of the particles.Among the three selected surfactants,dodecyl trimethyl ammonium bromide can significantly improve the hydrophobicity of the particle while reducing the surface tension of the solution.Therefore,it has the best dewatering performance on the inertinite.Lauryl polyoxyethylene ether reduced the moisture of the vitrinite to 21.54%at a dosage of 100 g/t;dodecyltrimethylammonium bromide reduced the moisture of the inertinite to 21.28%at a dosage of 3000 g/t.（4）The synergistic effect of flocculants and surfactants significantly enhanced the dewatering performance of macerals.Compared with the single filter aid,the synergistic effect of flocculants and surfactants enables reagents to have more adsorption methods on the macerals,which reduced the effect of a single filter aid on the wettability and surface potential of macerals,and further promoted floc agglomeration and improved the filter cake structure.The discussion of the mechanism showed that the synergistic effect two enhances the pore structure of the filter cake and achieves efficient dewatering of the macerals.The combination of nonionic flocculant and cationic surfactant has the best filtration aid effect.The moisture of the vitrinite and inertinite decreased to 15.80%and 16.53%,respectively,at the optimal dosage.This study not only explains the dewatering mechanisms of macerals,but also reveals the filtration mechanism of different filter aids for macerals based on the difference in adsorption behavior of filter aids on the surface of macerals.The research work will provide new views for solving the moisture problems existing in flotation clean coal,lay a theoretical foundation for the follow-up work of the National Natural Science Foundation project,enrich the flotation clean coal dewatering theory,and provide basis and reference for the development of new high-efficiency flotation clean coal filter aids.This dissertation includes 106 figures,16 tables,and 195 references. |
