Study On The Characteristics Of Filter Cake Structure Of Coal Slime

With the development of coal preparation technology,wet coal preparation occupies the main position in most coal preparation plants,which lead to remove the water from the final coal products.There always is filter cake during coal slime dewatering.While the filter cake structure affect the dewatering effect to a large extent.On the one hand,the filter cake structure was affected by the coal slime characteristics and coal slurry properties,on the other hand,the pharmaceutical system is also closely related to the filter cake structure.This paper mainly studied the dewatering test of coal slime under different conditions,and the cake structure under various conditions and its influence mechanism on the dewatering effect were analyzed.At the same time,the dynamic growth law of the cake was explored in the process of slime dewatering.The influence degree of each factor on the moisture content of the filter cake was analyzed by gray correlation method.The results were showed as follows:?1?The degree of metamorphism of coal samples has a significant effect on the dewatering effect of coal slurry,and the coal sample with medium degree of metamorphism has the best dewatering effect.The larger the size of the particle is,the smaller the resistance is,the higher the porosity is,the more smoothly theflow of water in the filter cake is.So the filtering velocity is faster.And the fractal dimension of the filter cake and the pore surface area decreased with the increasing of particle size.The water is easy to remove,which eventually reduce the cake moisture.Due to the enrichment of clay minerals in the density of1.4-1.6g/cm³ coal slurry,the resistance of the filter cake increases and the porosity decreases.Eventually the filtration effect becomes worse.?2?With the increase of coal slurry concentration,the porosity of filter cake is reduced,which make the dewatering more difficult.While fractal dimension increases,the pores surface is rougher leading to dewatering more difficult.The smaller the pH,the more the concentration of H⁺ in the coal slurry,which reduces the attractiveness of the particles surface to the water molecules leading to the particles separate from water easier.At the same time,with the decrease of pH,the porosity of the upper surface of the filter cake increases,the fractal dimension decreases,and the specific resistance of the filter cake decreases,which is favorable for dewatering.?3?With the progress of the filtration process,the fractal dimension of the pores increases,the porosity of the filter cake increases slightly and then decreases,and continuing filtration after the surface water disappeared can increase the porosity.The mathematical model on the porosity of the upper surface of the filter cake with the dehydration time is: y = 0.673x² – 9.982 x +40.37.The mathematical model on the porosity of the filter cake with the dehydration time is: y = 0.291x² – 4.223 x + 45.15.?4?The effect of various valence states and cationic and ions on the dehydration effect of coal slurry shows that when the anion is Cl^-,the monovalent cation K⁺ and Na⁺ can effectively reduce the moisture content of the filter cake.It is more obvious that divalent cation Mg²⁺ and Ca²⁺ reduce the moisture content of filter cake and improve the effect of dehydration.While Ca²⁺is better than Mg²⁺.The catalytic effect of Fe³⁺ and Al³⁺ is the best,and the stability of Al³⁺ is higher than that of Fe³⁺.When the cation is Na+,the dehydration effect of the anion Cl-is the best,SO₄^2-is the second,and NO₃^-is the worst.?5?Through the comparative analysis of the effect of slime dewatering under different agent systems,it can be seen that the cationic polyacrylamide has the best effect,and the optimum dosage is 150g/t.The filtration rate is0.09mL/s.cm².And the resistance is smallest,the porosity of upper layer is 31%,the fractal dimension is smaller at this condition which is most favorable for the filtration.?6?The gray correlation analysis result shows that the influence level of each factor on the moisture content of the filter cake is: particle size,coal slurry concentration,coal slurry pH,cationic polyacrylamide dosage,coal sample metamorphism,AlCl₃ dosage.