Principle And Practice Of Physical-Chemical Control Of The Pore Structure Of Coal Slime Filter Cake

In the context of peak carbon dioxide emissions and carbon neutrality,it is imperative to optimize and adjust the energy structure and use coal resources efficiently and cleanly.Slurry water is one of the main pollution sources in the coal industry,and effective coal slurry solid-liquid separation technology has become a key link in the clean utilization of coal.First of all,the present study explored the influence of chemical filter aids and skeleton builders on the effect of coal slime dewatering.On this basis,a physicochemical composite filter aid was designed to further improve the dewatering effect of slime.Secondly,the mechanism of interaction between different filter aids and coal slime particles was revealed through atomic force microscope,molecular simulation,and extended DLVO theoretical calculation,etc.,and the mechanism of skeleton supporting was analyzed.Moreover,low-field nuclear magnetic resonance technology and CT scanning technology were used to analyze the influence of the compound reagent on the moisture distribution of the filter cake and the optimization mechanism of the filter cake structure.Finally,through the particle flow numerical simulation,the dynamic growth law of the filter cake and the migration law of fine particles in the filter cake were analyzed,and the influence of different filter aids on the migration of slime particles and the regulation mechanism of the filter cake structure were studied.The main conclusions are as follows:(1)STAC could not only increase the filtration rate of slime water,but also reduce the moisture and the average mass specific resistance of the filter cake,and significantly improved the filtration effect.Both anionic polyacrylamide 5250 and non-ionic polyacrylamide 333 could significantly increase the filtration rate of slime and reduce the average mass specific resistance of the filter cake,while increased the moisture of the filter cake.Diatomite,perlite,and cellulose could all increase the filtration rate of slime to varying degrees and reduce the average mass specific resistance of the filter cake.Due to the large and uniform particle size of spherical SiO₂,it played a good framework support role in the slime filter cake,and the filtering effect was improved most obviously.Compared with a single filter aid,the GH type composite reagent designed in this paper further improved the filtration performance of coal slime.With the increase in the amount of Micron-SiO₂balls in the GH type compound reagent,the filtration rate increased significantly,and the filter cake moisture and filter cake specific resistance gradually decreased.(2)The AFM in-situ test results show that:In deionized water,the adhesion force between two coal surfaces decreased with the increase of pH and changed from negative to positive at pH 10.In the presence of Magnafloc5250,the obtained adhesion force was-2.71nN at pH 4,which was greater than that of pH 10.However,the largest flocculation force(-1.87 nN)and the broadest range of action(45 nm)were observed at pH 10,which supported the settling tests and floc size measurements well.STAC was adsorbed on the coal surface in clusters or short strips,which was mainly based on single-layer and multi-layer adsorption.The adsorption morphology of STAC molecules on the silica surface of kaolin presented the spots and dots appearance.The adsorption thickness was about 2 nm and 4 nm,which demonstrated that single-layer adsorption and double-layer adsorption had occurred.The adsorption of STAC molecules on the alumina surface of kaolinite was mainly manifested as patchy adsorption,and the adsorption height was mostly concentrated in 2-3 nm,suggesting that the single-layer adsorption occurred.At the same time,the molecular simulation results show that:Due to the-OH functional groups on the kaolinite 001 surface,additional water molecules were present between the kaolinite 001 surface and STAC,and these possibly act as a bridge in the adsorption of STAC on the kaolinite 001 surface.The nitrogen atoms of STAC were adsorbed nearer to the particle surface compared to the remainder of the STAC molecule.As a result,the alkyl chains of STAC projected into the water,and the movement of water molecules on the particle surface was less restricted,thus the hydrophobicity of coal and kaolinite increased,which improved the dewatering effect of coal slime.(3)The pores of the diatomite were mostly through holes,which were conducive to water circulation,while the pores of activated carbon were mostly blind holes,which could not form an effective water migration path.The filter cake formed by spherical SiO₂ had a larger porosity and was more conducive to dehydration.And the CT test results showed that the composite reagent could improve the porosity and pore connectivity of the filter cake.After adding the GH type compound reagent,the porosity of the filter cake increased from 1.54%to 6.67%.The pore coordination number of the filter cake increased significantly,and pores with a coordination number greater than 10 appeared,indicating that the skeleton builder can effectively improve the connectivity of the filter cake pores and create more paths for the migration of water during the filtration process,and thereby reduce the water content of the filter cake.Also,the radius ratio of pore/throat was reduced from 1.18 to 1.09,thereby reducing the capillary resistance during the water migration process,which significantly increased the filtration speed and improved the filtration effect.GH type compound agent can increase the degree of freedom of adsorbed water and bound water in the slime filter cake.With the increase in the amount of GH type compound reagent,the content of adsorbed water and bound water in the slime filter cake decreased from 99.059%to 96.214%,and the content of free water increased from 0.941%to 3.786%.(4)The large particles in the filter cake mainly slipped under the action of pressure,while the fine particles were caused to reduce the porosity of the filter cake due to the effect of migration and drilling.As the size of the fine particles decreased,the migration distance of the particles in the Y direction basically increased.For the main particles of the filter cake of 30?m,when the particle size of the fine particles was less than 15?m,the drilling phenomenon occurred significantly.Both surfactants can have a hydrophobic agglomeration effect on coal slime particles,increase the particle size,and then increase the porosity and looseness of the filter cake.After adding STAC,the migration phenomenon of fine particles was obviously weakened.The small flocs in the slime formed a relatively fluffy structure during the formation of the filter cake,which increased the thickness of the slime filter cake by 0.014 mm,the total porosity of the filter cake by 0.042,and the filtering effect was improved.Due to flocculation,polyacrylamide increased the particle size of the particles,formed a certain number of large flocs,reduced the migration of fine particles,and increased the porosity.The spherical SiO₂ increased the thickness of the slime filter cake by 0.014 mm and the total porosity by 0.041,which avoided the compression deformation of particles and reduced the migration of fine particles,thus improving the filtering effect of the slime.The filter cake structure formed by the GH-type composite reagent was looser,the thickness of the slime filter cake was increased by 0.034 mm,and the total porosity was also significantly increased,which further improved the dehydration effect of the slime.