Influence Mechanism Of Inorganic Salts On Settling Behavior Of Fine Clay And Regulation Of Interfacial Hydrophobicity

The existence of fine clay minerals is the main reason why it is difficult for slime water to settle,and the clay minerals in slime water are mainly kaolinite and montmorillonite.There are electrostatic repulsion and hydration repulsion between mineral particles,which make them disperse stably in the suspension,and then make it difficult for coal slurry to settle efficiently.In order to solve the problem that clay minerals seriously affect the settlement of coal slurry,this paper studies the influence of common inorganic salts(Na Cl,KCl,Ca Cl₂,Mg Cl₂)on the settlement behavior of fine-grained kaolinite and montmorillonite by means of experimental measurement and molecular dynamics simulation,DDA was used as a surfactant to control the sedimentation of fine clay.The adsorption behavior of DDA⁺on mineral surface was simulated to reveal the hydration characteristics of kaolinite and montmorillonite and the regulation mechanism of different agents on the sedimentation process,in order to provide guidance and reference for the efficient settlement treatment of coal slurry.The experimental results of sedimentation kinetics of inorganic salt ions on fine-grained clay show that kaolinite and montmorillonite suspensions show the same sedimentation kinetics and concentration effect.When the pulp concentration is the same,the sedimentation velocity first increases and then remains unchanged with the increase of inorganic salt concentration;when the concentration of salt ions is the same,the sedimentation velocity gradually decreases with the increase of pulp concentration,and then decreases The effect is getting worse.When the valence state of bivalent ion is higher than that of monovalent ion,the sedimentation effect is better than that of monovalent ion.The addition of salt ions will have a certain effect on the settlement of kaolinite and montmorillonite,but the overall settlement speed is slow and the settlement time is long,which indicates that there are other forces affecting the settlement of coal slurry.The test of interaction force between particles under different inorganic salt ions and concentrations shows that when the concentration of salt ions is the same,the action range of force is Ca Cl₂>Mg Cl₂>KCl>Na Cl;under the same salt ion condition,the ion concentration is less than 10^-3 When the ion concentration is 10^-1 mol/L,the electrostatic repulsion between particles is basically shielded,and there is no short-range jump in adhesion phenomenon,which indicates that in addition to electrostatic repulsion,the electrostatic repulsion between particles is another force that is difficult to settle.Molecular dynamics simulation of hydration characteristics of different metal cations on the surface of kaolinite and montmorillonite shows that due to hydrogen bonding,water molecules form three water molecular layers on the surface of kaolinite and montmorillonite,and with the increase of the distance between water molecular layers and surface,the binding force of surface to water molecules gradually weakens;the hydration ability of K⁺,Na⁺,Ca²⁺and Mg²⁺is in the order of Mg²⁺>Ca²⁺>Na⁺>K⁺.In this paper,the surface of kaolinite and montmorillonite was hydrophobically modified with DDA as surfactant.It was found that when the pulp concentration was the same,the sedimentation rate increased gradually with the increase of DDA concentration,and the sedimentation effect became better.With the increase of DDA concentration,the double-layer adsorption of reagent molecules on the mineral surface reduced the degree of hydrophobicity of mineral particles,resulting in the decrease of the sedimentation effect of suspension poor.The experimental study on the sedimentation kinetics of kaolinite and montmorillonite suspensions in the mixed solution of inorganic salt and DDA shows that with the increase of pulp concentration and inorganic salt concentration,the sedimentation velocity first increases and then decreases,which is consistent with the sedimentation law of kaolinite and montmorillonite suspensions under the action of DDA alone.However,the sedimentation effect of inorganic salt+DDA solution is worse than that of DDA alone,which indicates that metal cations can inhibit the sedimentation behavior of kaolinite and montmorillonite suspensions in DDA solution.The simulation results of DDA⁺adsorption on kaolinite and montmorillonite show that in the stable adsorption configuration of DDA⁺-kaolinite(001),most of the DDA⁺polar head groups are adsorbed on the surface,while a few are far away from the surface;in the stable adsorption configuration of DDA⁺-kaolinite(00^-1),some of the DDA⁺polar head groups are adsorbed on the surface in a horizontal way,and some of the DDA⁺polar groups are far away from the surface In the stable adsorption configuration of DDA⁺-montmorillonite(001),the polar head group of DDA⁺adsorbs vertically on the surface of montmorillonite,while the nonpolar tail chains attract each other due to hydrophobic interaction,and the carbon skeleton inclines.The hydrophilic polar group of DDA⁺adsorbs spontaneously on the surface of negatively charged kaolinite and montmorillonite particles by electrostatic attraction,while the hydrophobic non-polar group faces the solution,which makes the surface of particles hydrophobic and leads to hydrophobic aggregation during sedimentation.This paper contains 50 figures,3 tables and 92 references.