| The key processing in coal slime water treatment is the settlement of fine clay minerals,which will form difficult settled suspension in tailing treatment system.It brings difficulties to the purification and recovery of coal slime water,and also seriously affects every step in the coal washing processing.The surface charge characteristics of clay minerals have an important influence on the rheological behavior and the sedimentation effect of mineral particles in suspension.Illite mineral is the main component in clay minerals,so it is of great significance and practical value to study the surface properties of illite accurately and analyze the effect of the surface properties of illite anisotropic surfaces on the rheological property in suspension.This work could provide us a further understanding on the interaction characteristics of illite basal and edge surfaces and improve our insights on the colloidal behavior of clay suspensions.Firstly,in this study,the basal and edge surfaces of illite mineral were studied by atomic force microscope(AFM).Silicon nitride tip and silicon tip were used to measure interaction forces on basal/edge surfaces of illite mineral in 10 mM KCl solutions respectively under different pH values.Based on Derjaguin-Landau-Verwey-Overbeek(DLVO)theory,surface potentials of basal and edge surfaces of illite were obtained by fitting the interaction force curves.The results showed that when the solution pH value is 3.0,5.0,6.0,8.0 and 10.0,the surface potential of illite basal and edge surfaces is -58/-7 mV,-64/-28 mV,-67/-42 mV,-71/-51 mV and -75/-57 mV,respectively.Both the basal and edge surfaces showed negatively charged,but the basal surface exhibited more negative charges than the edge surface in the pH range studied.Surface potential of the basal surface changes slightly from pH 3.0 to 10.0,while surface potential of the edge surface decreases sharply with increasing pH value.The point of zero charge(PZC)of illite basal surface was not detected in the range of pH 3.0-10.0 in this study.The trend of surface potentials shows the PZC of edge surface is slightly lower than pH 3.0.Secondly,the interaction forces between illite basal/edge surface and Si3N4/Si tip with various concentration divalent cations in 10 mM KCl solution were measured using the AFM.The effect of divalent cation addition on the interaction forces were studied,and the surface potentials of the basal surfaces in divalent cations solutions were determined by fitting the measured forces with the classical DLVO theory.When the concentration of calcium or magnesium ions in the solution is 0,0.1mM,0.5 mM and 1 mM,the surface potential values of illite basal surfaces are about-71/-71 mV,-35/-37 mV,-30/-32 mV,-26/-28 mV,and-20/-22 mV,respectively.The fitted basal surface potentials became less negative with increasing calcium or magnesium concentration in pH 8.0 solution.Calcium or magnesium ions have similar magnitude of effect on the illite basal surfaces at pH 8.0.The electrostatic interaction was the major contribution to the interaction between divalent cations and illite basal surface in solutions at pH 8.0.When the concentration of calcium/magnesium ions in solution is 0,0.1mM,0.5 mM,1 mM and 5 mM,the surface potential values of illite edge surfaces are about-51/-51 mV,-41/-45 mV,-25/-35 mV,+19/-22 mV and +22/+13 mV,respectively.The main reason probably lies in that calcium and magnesium ions could form surface complexes with the hydrolyzed broken SiOH or AlOH groups on illite edge surfaces.Furthermore,because calcium ions seem to get close to the edge surface easier than magnesium ions,the calcium ions are more effective in reducing the magnitude of surface potentials than magnesium ions.Finally,the theoretical model for calculating the interaction energy between different surfaces was introduced.According to the DLVO theory,the intercation energy between illite anisotropic surfaces in solutions with different pH values was calculated through the surface potential values of illite basal and edge surfaces.The shear yield stress of illite particles in the corresponding pH in suspension was measured,and the reasons for the associations of illite particles in the solution were analyzed based on the interaction energy.In the meanwhile,the interaction energies between illite anisotropic surfaces in solutions of calcium ion and magnesium ion were also calculated and studied.The results are shown below: the interaction energies between basal and basal surfaces are strong repulsive in the range of pH 3.0 ? 10.0.The interaction energy between edge and edge surfaces is repulsive in the range of pH 5.0 ? 10.0,and it decreases with the decreasing of pH value.When the pH drops to 3.0,the interaction energy changes from repulsive to attractive.The interaction energy between the basal and edge surfaces has the similar trend with the interaction energy between edge and edge surfaces.The shear yield stress of illite suspension is maximum in the solution with a pH of 3.0.The shear yield stress drops sharply at pH 4.0.Further increasing the value of pH,the shear yield stress decreases gradually.The main reasons for this rheological phenomenon are as follows: at pH of 3.0,the repulsive energy between the edge and edge surfaces decreases slightly,but the interaction between the basal and edge surfaces becomes the attractive,which leads to the three-dimensional "card-house structure".When the pH value of the solution is 5.0,the repulsive energy between the edge and edge surfaces reduces significantly,while the repulsive energy between the basal and edge surfaces reduces slightly.The association of the basla and edge surfaces in the suspension will change slightly,and some edge and edge surfaces association will be formed.In the solution with pH greater than 6.0,there are obvious repulsive energies between basal and basal surfaces,edge and edge surfaces,basal and edge surfaces.Thus,the shear yield stress of the suspension is small.When the concentration of calcium or magnesium ion varies from 0 to 5 mM,the interaction energies between basal and basal surfaces are all repulsive.When 0.1mm of calcium or magnesium ion is added,the repulsive energies reduce significantly.As the concentration of calcium or magnesium ion continues to increase,the repulsive energies reduce a little.The interaction energy between edge and edge surfaces is repulsive when the concentration of calcium or magnesium ion is 0 ? 0.5 mM.The interaction energy converts to attractive when the concentration of calcium ion is 1 mM,and the transformation of magnesium ion changes into attractive when the concentration is 5 mM.The interaction energy between the basal and edge changes from repulsive to attractive when the concentration of calcium ion is 1 mM.When the magnesium ion concentration reaches to 5 mM,the interaction energy between the basal and edge surfaces changes to attractive.This dissertation contains 61 figures,3 tables and 175 references. |
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