Structural evolution of coal sludge filter cake and optimization mechanism of combined chemicals in the process of filtration pressing
The structure of coal sludge filter cake has an important influence on the dewatering effect.In this study,the characteristics of the filter cake structure and its evolution law in the process of filter press dewatering were investigated by using the homemade pressurized dewatering device and CT scanning methods.The filter press process was modified into four stages.Among them,the cake dewatering stage mainly removes the internal water of the cake,and the more de-veloped the pore structure of the cake in this stage,the better the dewatering effect of the filter press;the cake compres-sion stage mainly compresses the cake at last,and the higher the compression of the cake in this stage,the lower the poros-ity and water content of the cake will be in the end.The polymerised ferric sulphate(PFS)and α-hemihydrate gypsum(α-HH)were used to carry out filtration aid experiments on coal slurry.The filtration-assisting mechanism was analyzed from various aspects,such as the flocculation structure of coal slurry particles,the composition of the physical phase of the fil-ter cake,and the three-dimensional structure of the filter cake.The results showed that the combination of PFS and α-HH significantly enhanced the filtration effect of coal slurry,and the optimal dosage of the two was determined to be 1 711.44 g/t and 48.33 mg/g by central combinatorial design(CCD).Under the optimal conditions,the water content of the filtrate cake was reduced to 16.97％and the filtration rate was increased to 145.89 mL/(s·m2).The addition of α-HH made the absolute value of filtrate zeta potential to 1.45 mV,which reduced the electrostatic repulsive force between coal slurry particles,enhanced the flocculation effect of PFS,and increased the chord length of flocs to 71-171 μm.Mean-while,in the PFS system,the hydration reaction of α-HH was accelerated,and a large number of gypsum dihydrate crys-tals were formed,which formed the intertwined skeleton in the flocs of coal slurry,and played the role of the skeleton con-structor.These gypsum dihydrate crystals increase the index of compression dehydration(ICD)of coal tailing filter press to 176.30.The pore size of coal slurry filter cake was increased from 12.14％to 14.39％during the filtration process,which im-proved the pore coordination number and connectivity of the coal slurry filter cake and thus improved the filtration effect.
coal slurry dewateringskeletal constructsCTfilter cake structurefiltration process
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