Study On Solid-liquid Separation Of Na-montmorillonite Based On Rheological Properties

Montmorillonite is always a troublemaker for the dewatering in coal processing since its existence can decrease the rates of sedimentation and filtration of coal slurry.To eliminate the adverse effect of montmorillonite,adjusting the slurry p H and adding electrolytes are always the key methods.However,the underlying mechanism still needs to be further studied.In this paper,the effects of the suspension environment,such as particle concentration,p H and ion concentration,on the sedimentation and filtration properties are studied.According to the apparent viscosity and shear stress of the Na-montmorillonite（Na-Mt）suspension,the yield stress of suspension is calculated by Herschel-Bulkley model.The effects of the suspension environment on the flow behavior of Na-Mt and the strength of the particle network structure are analyzed.The solid-liquid separation mechanism of Na-Mt was studied from the perspective of the interaction between different surfaces of the particles.The results show that:（1）In the range of 0.6-30.0 g/L,Na-Mt suspensions were not settle spontaneously.With increasing the particle concentration of Na-Mt suspension,the filtration performance was decreased.When the p H value of the suspension is2.5,Na-Mt formed flocs and coagulated spontaneously.Under the condition of faintly acid and alkali,the Na-Mt suspension was dispersed.The filtration performance of Na-Mt was the worst at the original p H.However,it is obviously improved in the strong acid environment of suspension.The effect of ion concentration on the sedimentation performance is obvious.Na-Mt can also coagulate in the faintly acid suspension,after adding 10^-3 M ion concentration.And at 10^-1 M ion concentration,Na-Mt can settle in the whole p H range.With strong acid environment of suspension,the filtration performance is not affected by the formation of filter cake in the filtration process.But in faintly acid and alkaline conditions,the filtration performance increases with the increasing p H and ion concentration.（2）The apparent viscosity of Na-Mt suspension increased with the increase of particle concentration.Under the same p H condition,the apparent viscosity of Na-Mt was increased with the increase of ion concentration.And under the same ion concentration,the apparent viscosity was decreased with the increase of p H.In the whole p H range,the yield stress of Na-Mt suspension was increased with the increase of ion concentration.（3）Na-Mt formed a three-dimensional edge-face association structure in the suspension of low ion concentration and acid condition,which is conducive to sedimentation.But this structure is relatively closed and has large structure space,which is adverse to squeeze out water molecules in the filtration process.While the face-face association structure formed with high ion concentration under alkaline condition can also promote the sedimentation performance of Na-Mt suspension.Moreover,the face-face structure has small layer space,and there are less water molecules in the structure space,which promotes the filtration performance of Na-Mt suspension.Therefore,adjusting the suspension condition to change the coagulation behavior of particles is one of the effective methods to solve the Na-Mt solid-liquid problem.