| Clay minerals are the main minerals in coal slurry water.Hydration of clay particles surface in coal slurry water lead to the formation of elastic hydration layers on the surfaces,which prevents particles aggregation and weakens coal slime dewatering.illite,one of the main clay minerals in coal slurry water,is studied.The studies of surface hydration characteristics and mechanism of illite particles at the microscopic level can provide theoretical basis for the development of new technology of coal slurry water sedimentation and dewatering,which is of great significance for the clarification treatment of high muddy coal slurry water.The aggregation of illite with other particles and hydration on fine illite particles in coal slurry water have been studied by theoretical calculation and experimental test.The results show that as the dissociation degree of illite increases,the particle changes from spherical shape to sheet shape,which worsens the sedimentation of coal slurry water.The hydration film on illite surface can weaken the Van Der Waals interaction potential energy between particles.The metal cation hydration in the double electric layer of the particle can increase the electrostatic interaction potential energy between particles.The hydration film of particles can repel each other.All of them are not conducive to the sedimentation of coal slurry water.The hydration index of illite particles,which characterizes the hydration degree,with high dissociation degree is higher than that of illite particles with low dissociation degree.With the increase of pH,the hydration index of illite particles increased slightly.The hydrations index of illite in different aqueous electrolyte solutions decreased in the order of Al3+>Mg2+>Ca2+>Na+>K+.As the concentrations of metal cation increased,more hydrated cations were adsorbed on the illite surface,which leads to a higher hydration degree until the solution reached an adsorption equilibrium.The effect of different lattice substitutions on the electronic structure of illite has been studied by density functional theory.The results show that the illite structure cell is the most stable when the lattice replacement(Al3+?Si4+)location is the para-position distribution.The higher the cationic potential is,the smaller the interlayer spacing is.The adsorption of K+on(001)surface is mainly based on electrostatic interactions,and that of NH4+ is mainly based on covalent interactions.The order of adsorption energies of different cations on(001)surface is K+<Na+<NH4+<Ca2+<Mg2+.The adsorption energies of cations increase as the increasing of the proportion of lattice substitution.Lattice substitutions enhance the activity of the oxygen atoms of(001)surface near substitutions and enhance the acidity and alkalinity of the hydroxyl groups of(010)surface near substitutions.The adsorption of water molecules on illite surfaces have been studied by density functional theory.The results show that the adsorption configurations of water molecule are affected by NH4+,K+ and active O atoms of illite(001)surface,and the adsorption energies are-0.67 eV and-0.55 eV,respectively.On(010)surface,the presence of K+prevents water molecules from entering into layers,and the surface hydroxyl groups affect the adsorption configuration of water molecules with the adsorption of-0.91 eV.There are hydrogen bond and electrostatic interaction between water molecules and surfaces.The adsorption of water molecules on(010)surface is stronger than that on(001)surface,and with the increase of the edge surface,the adsorption position of water molecules on(010)surface increase,resulting in the increase of the strength of hydration layers on surface.The adsorption of hydronium ions and hydroxyl ions on illite surfaces have been studied by DFT.The results show that on illite(001)surface,H2O adsorbed on Si-O atoms ring easily obtain a proton,and H3O+ prefers to be adsorbed above the holes of the Si-O atoms ring.On illite(010)surface,=Al-OH can get one proton from H3O+easily,and there is a competitive adsorption between H2O and H3O+.OH-adsorption on(001)surface is an endothermic reaction,which cannot be spontaneously adsorbed on surface.The OH" preferentially forms coordination bonds with the substituted atom A1 in tetrahedron sheet of illite.The adsorption of OH-on(010)surface enables water molecules to gain 0.04 e charge,which contributes to the electrostatic interaction of the water molecules with cation.The kinetic characteristics of hydrated layers and metal cations at the illite-water interface have been studied by molecular dynamics.The results show that the water-illite interface properties are affected by surface charge.As the surface charge of illite increases,some of the interface properties can be enhanced,including the density of hydration layers and the constraint of K+ ions in diffusion layers,however,the other part of the interface properties can be weakened,including the thickness of the stern layer and the diffusion coefficient of interfacial water molecules.The hydration number of metal cation at the water-illite interface is greater than that at the bulk water phase.The main adsorption positions of K at the water-illite interface are located at 1.6A and 2.5A away from(001)surface,and that of Na are at 2.0 A and 4.0 A,and Ca2+and Mg2+are at 2.0 A and 4.0 A,respectively.K+and Na+ are mainly adsorbed at siloxane of Si4Al2O6,and Ca2+and Mg2+ are mainly adsorbed at holes of siloxane of Si4Al2O6 and AlO3.The adsorption of K+,Na+,Ca2+and Mg2+on(001)surface can increases the degree of order and viscosity of water at the water-illite interface.At the same distance from the surface,the diffusion coefficient of water molecules at water-illite interface with different balance cations follows this sequence:Mg2+<Ca2+<Na+<K+.If the hydration layers were separated from the body phase at the same diffusion coefficient,the thickness of hydration layers at water-illite interface with different balance cations decreased as:Mg2+>Ca2+>Na+>K+,which is consistent with the experimental test results.Figure[80];table[37];reference[164]... |
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