Characteristics And Mechanism Research On Hydrophobic Aggregation Of Fine Particles In High Muddied Coal Slurry Water

Coal slurry water is a kind of industrial waste water produced in wet coal separation,and its clarification treatment is an essential link in the processes of coal preparation plants.However,due to the mechanization of coal mining and the deterioration of raw coal,lots of high muddied coal slurry water is produced in coal preparation plants.The high muddied coal slurry water has characteristics of extraordinary fine granularity,high clay mineral content,and strong electronegativity of particle surfaces,which increases the difficulty of the settlement and clarification of coal slurry water.In this paper,the samples of the high muddied coal slurry water of coal preparation plant in Huainan,coal and kaolinite were taken as the research objects.The combined method of quantum chemistry/molecular dynamics simulation and experimental verification was used to lucubrate the characteristics and mechanism on hydrophobic aggregation of fine particles in high muddied coal slurry water,which can provide a theoretical basis to develop new technologies and design new drugs of sedimentation and clarification for coal slurry water.The research results of characteristics on hydrophobic aggregation of fine particles in coal slurry water with hydrophobic modification agents show that the cationic hydrophobic modification agents can adsorb on fine slurry particle surfaces of negatively charged by electrostatic attraction,which can enhance the hydrophobicity,reduce the electronegativity of particle surfaces,and promote the hydrophobic aggregation of particles under the action of hydrophobic interaction,then promote the hydrophobic aggregation settlement of fine particles in coal slurry water.Under the action of hydrophobic modification agents,the aggregation settlement effect of coal particles was weaker than that of the kaolinite particles.Reagent type and reagent dosage,energy input,pulp concentration and pH value are the main factors to influence the hydrophobic aggregation settlement effect of fine slurry mineral particles.Reagent type and reagent dosage influence the hydrophobic aggregation settlement effect mainly by impacting the size of hydrophobic aggregation.The appropriate pulp concentration and energy input are favorable for the hydrophobic aggregation of fine slurry mineral particles.Moreover,the best pulp pH of the fine coal slurry mineral particles is weakly alkaline.The hydrophobic aggregation settlement effect of the coal slurry water of D and L are good when the dosage of 1831 is 3000 g/t,the stirring intensity is 750 r/min and the stirring time is 10 min,the settling velocity and the light transmittance are 0.83 cm/min,78.6%and 1.31 cm/min,62.4%,respectively.Using the mixture of coagulant and hydrophobic modification agent,not only can reduce the reagent dosage,but also can effectively improve the hydrophobic aggregation settlement effect of high muddied coal slurry water.The optimum distribution of the dosage of coagulant and 1831 is 40 g/t APAM,10000 g/t CaCl₂ and 1500 g/t 1831,the settling velocity is 0.97 cm/min and the light transmittance is 84.1%under this conditions.The DFT simulation results of the adsorption on coal surface show that the adsorption of water molecule on coal surface mainly by forming the hydrogen bonds with different oxygen functional groups of coal particle surface,and the stability of water molecule adsorption on different oxygen functional groups in the order of:-COOH>-C=O>Ph-OH>-O-.The adsorption of different methyl amine/ammonium cationics on coal surface mainly by forming hydrogen bonds of N-H...O or C-H...O with different oxygen functional groups of coal particle surface,and the stability of methyl amine/ammonium cationics adsorption on different oxygen functional groups in the order of:-C=O>-COOH>-O->Ph-OH.And the stability of Water and methyl amine/ammonium cations adsorption on oxygen functional groups of coal surface in the order of:H₂O>CH₆N⁺>C₂H₈N⁺>C₃H₁₀N⁺>C₄H₁₂N⁺,namely the state of different methyl amine/ammonium cations adsorption on the surface of oxygen functional groups is not stable in the aqueous environment.The DFT simulation results of the adsorption on coal surface show that the adsorption of water molecule on kaolinite（001）surface and（001）surface mainly by forming the hydrogen bonds,the adsorption energy of single water molecule on different initial position of kaolinite（001）surface is-72.12～-19.23 kJ/moL,less than the adsorption energy of single water molecule on different initial position of kaolinite（001）surface with-19.23～-5.77 kJ/moL,namely water molecules more easily adsorbed on kaolinite（001）surface.The adsorption of different methyl amine/ammonium cationics on kaolinite（001）surface and（001）surface mainly by electrostatic interaction and hydrogen bonds,and different amine/ammonium cationics more easily adsorbed on kaolinite（001）surface.The optimum adsorption sites of different methyl amine/ammonium cations on kaolinite（001）surface are all H3,and the adsorption energies（in order to primary amine cationic,secondary amine cationic,tertiary amine cationic and quaternary ammonium cationic,the same below）are-125.385,-126.154,-128.654 and-109.711 kJ/mol,respectively.And the optimum adsorption sites of different methyl amine/ammonium cations on kaolinite（001）surface are all H1,and the adsorption energies are-140.961,-136.154,-138.558 and-115.961 kJ/mol,respectively.The stability of different dodecyl amine/ammonium cationics adsorption on different hollow sites of kaolinite（001）surface in the order of:H3>H2>H1,and the stability of different dodecyl amine/ammonium cationics adsorption on different hollow sites of kaolinite（001）surface in the order of:H1>H2>H3.The stability of different quaternary ammonium cationics adsorption on kaolinite（001）surface and（001）surface decreases with the increase of carbon chain length.The adsorption of different coal oxygen structural units on kaolinite（001）surface and（001）surface mainly by forming the hydrogen bonds of its oxygen functional group with kaolinite surface,the adsorption stability on kaolinite（001）surface and（001）surface in the order of:-COOH>Ph-OH>-C-=O>-O-and-COOH>-C=O>-O->Ph-OH,respectively.And different coal oxygen structural units more easily adsorbed on kaolinite（001）surface.The MD simulation results of water molecules adsorption on the bituminous coal surface show that as the number of water molecules in the water shell increased from 200 to 1600,interface effect of the coal surface on water molecules gradually decreases,and water molecules gradually away from the surface and the differentiation among water molecules decreased gradually.According to the MD simulation results of the hydrophobic modification agent adsorption on the interface between coal/water,the carbon chain of dodecyl primary amine cations and octadecyl trimethyl ammonium chloride cations undergo serious torsion after the equilibrium,and most of the cationic polar heads are oriented towards the solution,and the hydrophobicity modification effect on bituminous coal is not ideal.The MD simulation results of water molecules adsorption on the kaolinite surface show that the binding force between kaolinite surface and water molecules decreased with the increase of water coverage from 2/3 ML to 8/3ML,the hydrogen bond gradually weakened,and the water molecules gradually formed a number of water molecules shells.And at the same water coverage,the interfacial effect of kaolinite on water molecules is weaker than that of kaolinite（001）surface.According to the MD simulation results of hydrophobic modification agent at the bituminous coal/water interface,the dodecyl primary amine cations and octadecyl trimethyl ammonium chloride cations are mainly adsorbed on the kaolinite surface with polar head groups after the equilibration,and the nonpolar carbon chains are oriented towards the solution and undergo a certain degree of torsion.The cationic carbon chains are attracted together by hydrophobic association to hydrophobize the surface.The benzene rings in bituminous coal molecule were sapproximate parallel with the surface of kaolinite after the dynamic equilibrium of bituminous coal molecule on kaolinite（001）surface and（001）surface.The results further instructions that there are strong interactions between benzene rings and kaolinite surfaces,namely that the mechanism of interaction between coal and kaolinite fine particles should be the result of hydrogen-bond interaction and the interactions between benzene rings and kaolinite surfaces.The action mechanism of hydrophobic aggregation with hydrophobic modification agents of amine/ammonium salts should be the result of the action of"adsorption charge neutralization" and hydrophobic attraction.The Function mechanism of hydrophobic aggregation settlement of high muddied coal slurry water with hydrophobic modification agents mainly is that hydrophobic modification agent cationic through electrostatic attraction and hydrogen bonds adsorption on the surface of fine coal mineral particles,and then hydrophobic modification of particles surface would weaken the hydration repulsion between the particles and enhance the hydrophobic attraction between the particles.Meanwhile,the electronegativity of the surface of the slurry particles was reduced,the double electric layer was compressed and the electrostatic repulsion between the particles was reduced,which can promote the hydrophobic aggregation sedimentation of particles.